Sustainable fabrication of plant cuticle-like packaging films from

Subscriber access provided by Kaohsiung Medical University

Article

Sustainable fabrication of plant cuticle-like packaging films from tomato pomace agro-waste, beeswax, and alginate Giacomo Tedeschi, Jose Jesus Benitez, Luca Ceseracciu, Keyvan Dastmalchi, Boris Itin, Ruth E. Stark, Antonio Heredia, Athanassia Athanassiou, and José Alejandro Heredia-Guerrero ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03450 • Publication Date (Web): 10 Sep 2018 Downloaded from http://pubs.acs.org on September 10, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Sustainable fabrication of plant cuticle-like packaging films from tomato pomace agro-waste, beeswax, and alginate Giacomo Tedeschi1, 2, *, José Jesús Benitez3, Luca Ceseracciu4, Keyvan Dastmalchi5, Boris Itin6, Ruth E. Stark5, 7, Antonio Heredia8, 9, Athanassia Athanassiou1, * and José A. Heredia-Guerrero1, *

1

Smart Materials, Istituto Italiano di Tecnologia, Via Morego 30, Genova, 16163, Italy

2

DIBRIS, Università di Genova, Via Opera Pia 13, 16145, Italy

3

Instituto de Ciencia de Materiales de Sevilla, Centro mixto CSIC-Universidad de Sevilla, Calle

Americo Vespucio 49, Isla de la Cartuja, Sevilla, 41092, Spain 4

Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genova, 16163,

Italy 5

Department of Chemistry and Biochemistry,The City College of New York, City University of New

York and CUNY Institute for Macromolecular Assemblies, 85 St. Nicholas Terrace, New York, NY 10031, United States 6

New York Structural Biology Center, 89 Convent Ave, New York, NY 10027, United States

7

Ph.D. Program in Chemistry, CUNY Graduate Center, 365 Fifth Avenue, New York, NY 10016,

United States 8

Instituto de Hortofruticultura Subtropical y Mediterránea (IHSM) La Mayora, Universidad de

Málaga-CSIC, Avenida Dr. Wienberg, Algarrobo-Costa, Málaga 29750, Spain 9

Departamento de Biología Molecular y Bioquímica, Universidad de Málaga, Av. de Cervantes 2,

Málaga 29071, Spain -1ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 40

* Corresponding authors: [email protected], [email protected], [email protected]. Abstract Plant cuticles have been used as models to produce hydrophobic films composed of sodium alginate, the fatty acid fraction of tomato pomace agro-waste, and beeswax. The fabrication process consisted of the blending of components in green solvents (water and ethanol) and a subsequent thermal treatment (150°C, 8 h) to polymerize unsaturated and polyhydroxylated fatty acids from tomato pomace. When sodium alginate and tomato pomace fatty acids were blended, free-standing films were obtained. These films were characterized to evaluate their morphological (SEM), chemical (solid-state NMR, ATR-FTIR), mechanical (tensile tests), thermal (TGA), and hydrodynamic (water contact angle, uptake, and permeability) properties. A comparison between non-polymerized and polymerized samples was carried out, revealing that the thermal treatment represents a sustainable route to create structured, composite networks of both components. Finally, beeswax was added to the blend with the same amounts of sodium alginate and tomato pomace fatty acids. The presence of the wax improved the hydrophobicity and the mechanical and water barrier properties as well as decreased the water uptake. These results indicate that polymerized plant cuticle-like films have valuable potential for packaging applications.

Keywords: tomato pomace, agro-waste, cutin, plant cuticle, sodium alginate, beeswax, packaging.

-2ACS Paragon Plus Environment

Page 3 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction Nowadays, petroleum-based plastics are extensively used to fabricate most of the commodities used in everyday life. In particular, a 39.9% (134 million tons) of the global production of plastics in 2016 was dedicated to the production of packaging materials 1. In the case of food packaging, polypropylene (PP), high- and low-density polyethylene (HDPE and LDPE, respectively), and polyethylene terephthalate (PET) are the most demanded petroleum-based plastics. They are lowcost, easily processed materials with a wide range of mechanical properties, excellent transparency, and good hydrophobicity and water and gas barrier properties

2-3

. However, their massive use for

single use disposable packages, i.e. throw-away items, is contributing to the increased environmental pollution rate, due to the use of harmful chemicals during their production process, including monomer production (in particular, those that derive from the hydrocarbon cracking such as ethylene, propylene, butane, styrene, vinyl chloride, etc), and their high resistance to biodegradation 4-5. Despite the efforts to recycle petroleum-based plastics, a recent global analysis of all mass-produced plastics ever made, including thermoplastics, thermosets, polyurethanes, elastomers, coatings, and sealants, report that only 9% of them has been recovered by using this strategy 6. Thus, the design and the production of biodegradable materials with similar properties to the plastic ones is considered a more sustainable and realistic alternative 7. In fact, there are many commercially available bio-based and biodegradable that currently are used for bulk applications such as bio-chemosynthetic polymers (e.g., poly(lactic acid), poly(butylene succinate)), biosynthetic polymers (e.g., polyhydroxyalkanoates), and modified natural polymers (e.g., starch polymers, cellulose derivatives) 8. Among the different approaches used to overcome petroleum-based plastics’ drawbacks (i.e., non-biodegradability, lowsustainability), the design of biomimetics of natural systems is giving rise to green and commercially available systems 9. A natural system that has attracted the attention of scientists, who try to mimic it, is the plant cuticle, the outermost membrane that covers the epidermis of non-lignified plant organs such as petals, leaves, stems and fruits 10-11. The main functions of the plant cuticle are related to the -3ACS Paragon Plus Environment


Page 4 of 40

prevention of water loss from internal tissues, the regulation of the gas exchange, and the protection against biotic (pathogens, insects) and abiotic (relative humidity, temperature, radiation) stresses and mechanical damages 11-12. These characteristics make the cuticle an ideal system that bio-based food packaging materials could mimic 13. It is mainly composed of cutin (a long-chain polyhydroxylated polyester), but it also includes polysaccharides (mostly cellulose, hemicelluloses, and pectin) from the cell wall, and a minor fraction of waxes found either on the plant surface (epicuticular waxes) or inside the cuticle (intracuticular waxes) 14. Recently, cutin, together with other biopolymers such as cellulose, lignin, chitin, and silk, have been considered potential substitutes for conventional plastics for specific uses, as part of a wider strategy of reducing marine plastic litter and microplastics 15. In fact, pure cutin and cutin-like bioplastics have been made into free-standing films with applications in food and cosmetic packaging 16-17. To improve the mechanical and barrier properties as well as the hydrophobicity of these materials, cutin monomers have also been combined and polymerized with different polysaccharides (e.g., pectin and cellulose) and carnauba wax 18. Usually, cutin monomers are obtained after a multistep procedure: first, cuticles are isolated from plant epidermis by enzymatic treatment, then, cutin is obtained after dewaxing in organic solvents and acid hydrolysis of the plant cuticles, and, finally, cutin monomers are derived from the basic hydrolysis of cutin and precipitation in acid media 19-21. As a whole, this process is time consuming and not cost-effective for large-scale technologies; it would be preferable to employ simpler methodologies where cutin-rich agro-wastes are directly subjected to the last step 22-23. This latter option is available for tomato pomace, an agrowaste from the food processing industry, after the preparation of juices, pastes, purées, ketchup, sauces, and salsas. Tomato pomace consists mainly of peel and seeds and its global volume can reach 0.85 x 106 tons per year 24-25. The fatty fraction of this agro-waste is composed by polyhydroxylated fatty acids from cutin (82% 10,16-dihydroxyhexadeconoic acid and minor fractions of other multifunctional fatty acids such as 3% 16-hydroxyhexadecanoic acid and 3% 9-hydroxy-1,16hexadecanedioic acid) and unsaturated fatty acids from seeds (50% linoleic acid, 20% oleic acid, and minor fractions of other unsaturated and saturated fatty acids with different chain length) 26-27. -4ACS Paragon Plus Environment

Page 5 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In this work, we have blended tomato pomace fatty monomers with sodium alginate and beeswax in order to imitate natural plant cuticles. Sodium alginate is a natural polysaccharide derived from marine plants, especially from the cell walls of brown algae, whose structure consists of linear unbranched polymers composed of β-D-mannuronate (M) and α-L-guluronate (G) residues covalently linked with (1-4) glycosidic bonds

28-29

. It is non-toxic and water soluble and used in

different applications such as food additives and packaging, biomedicine, wound dressings, and textiles in the form of films, fibers, and gels 30-32 33-34 35-38. On the other hand, beeswax, a natural wax produced by Apis bees, consists of 71% wax esters, 15% hydrocarbons and 14% wax fatty acids 39. It is employed in packaging materials, to enhance barrier properties 40-41. Here, to mimic the natural cuticle model consisting of a polysaccharide substrate, a polyester framework and a wax phase, plant cuticle-like films composed by sodium alginate, tomato pomace fatty monomers, and beeswax were fabricated by simple blending in green solvents (water and ethanol) 42, drop-casting, and melting polycondensation. The effect of different amounts of tomato pomace fatty monomers and their polymerization by melting polycondensation on the morphology, wettability, and mechanical, thermal, and barrier properties of sodium alginate matrices was investigated. Finally, we show how the addition of beeswax modifies water barrier and mechanical properties of the plant cuticle-like films. Experimental section Materials Alginic acid sodium salt, beeswax, and ethanol were purchased from Sigma-Aldrich and used without further purification. Ultrapure water was produced by using a Milli-Q system (Q-POD Element, Merck Millipore). Polyhydroxylated and unsaturated fatty acids were obtained by alkaline hydrolysis of pomaces resulting from the industrial processing of tomato fruits to produce sauces and paste

22

.

They contained skins, seeds and fibers. Briefly, the crushed dry residue was previously washed with -5ACS Paragon Plus Environment


Page 6 of 40

a refluxing mixture of hexane:ethanol (1:1, v:v) and then ground to facilitate the alkaline attack. The hydrolysis was carried out at 100°C for 6 hours using a 0.5M NaOH solution in water. The resulting suspension was filtered after cooling to room temperature and the supernatant (polysaccharide fraction) was discarded. The solution was acidified with 3M HCl up to a final pH of 3. The precipitate was mostly constituted of aliphatic carboxylic acids and was separated by centrifugation. Several redispersion in water and centrifugation cycles were performed to completely remove the residual embedded NaCl. The solid was dried under vacuum for several days and stored at 4°C until use. Preparation of sodium alginate/tomato pomace composite films Sodium alginate and tomato pomace monomers blends were prepared by mixing both components in an ethanol:water mixture, drop-casting, and evaporation of the solvents. Sodium alginate solutions with a concentration of 30 mg/mL were prepared in ultrapure water at 60°C and with continuous stirring. On the other hand, tomato pomace monomers were added to a mixture of ultrapure water and ethanol (1:1, v:v) at a concentration of 30 mg/mL and dispersed by four successive 30-s ultrasound cycles using a 3.2 mm diameter tapered microtip at 10% amplitude attached to a VCX 750 ultrasonic processor (Sonics & Materials, Inc.). Then, the sodium alginate solution and tomato pomace monomers suspension were blended in five different weight ratios (sodium alginate/tomato pomace monomers: 100/0, 75/25, 50/50, 25/75, 0/100). Afterward, 25 mL of each solution was drop-casted on 9 cm diameter glass Petri dishes and warmed up in oven at 50°C for several hours until fully dry. Free-standing films were obtained for 100/0, 75/25 and 50/50 proportions. 25/75 and 0/100 combinations were very pasty and did not form films. The esterification of tomato pomace monomers was achieved by melting polycondensation. For this, films were placed in an oven for 8 hours at 150°C, as reported elsewhere 43. When waxes were added, the following procedure was used. 0.2 g of beeswax were dispersed in 20 mL of boiling water to melt them, producing a milky opaque suspension. The suspension was treated -6ACS Paragon Plus Environment

Page 7 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with 1-minute ultrasound cycles using a VCX 750 ultrasonic processor (Sonics & Materials, Inc.) at 40 kHz and then sonicated for 2 h at 35°C and 40 kHz in a bath sonicator (LCD Series, FALC). After that, the beeswax dispersion was added to the 50/50 sodium alginate:tomato pomace monomers solution in three different percentages respect to the total amount of polymer (5, 15, and 30 wt.%). The evaporation of solvents and the polymerization were the same as those described above. The final percentages of sodium alginate, tomato pomace monomers, and beeswax used in the different samples fabricated and their corresponding labels are summarized in Table 1. Table 1. Labeling and final formulation of the samples. Treatment

Sodium Alginate/Tomato Pomace Monomers blending

Thermal treatment (8 h, 150°C) (p: polymerization)

Beeswax addition + Thermal treatment (8 h, 150°C)

Label

Concentration of sodium alginate (wt.%)

Concentration of tomato pomace monomers (wt.%)

AT-0

100

0

Concentration of beeswax (wt.% with respect to the total amount of polymer) -

AT-25

75

25

-

AT-50

50

50

-

AT-75

25

75

-

AT-100

0

100

-

AT-0p

100

0

-

AT-25p

75

25

-

AT-50p

50

50

-

AT-75p

25

75

-

AT-100p

0

100

-

B-0

50

50

0

B-5

47.6

47.6

4.8

B-15

43.5

43.5

13

B-30

38.5

38.5

23



Page 8 of 40

Characterization Morphological characterization. Scanning electron microscope (SEM) images were acquired by using a JEOL JSM-6490OLA, operating at 10 kV acceleration voltage. All the samples were coated with a 10 nm thick film of gold. In order to analyse the top-view and the cross-section morphology of the samples, the imaging operation was carried out with secondary electrons. Chemical characterization. For solid-state

13

C NMR, a 4-channel Bruker Avance I 750/89

spectrometer (150 MHz 13C, Bruker Biospin, Karlsruhe, Germany) was used to acquire quantitatively reliable

13

C direct polarization–magic angle spinning (DPMAS) spectra. The instrument was

equipped with a 4-mm HXY probe in which ~70 mg samples were each spun at 15.00 ± 0.02 kHz and a temperature of 296 K. Spin echo experiments with pulses of 5.25 µs (13C 90º), 10.5 µs (13C 180º), and corresponding delays of 67 and 64 µs were used to obtain the spectra

44

. During an

acquisition time of 15 ms, we applied 80 kHz of 1H TPPM decoupling 45. A total of 264 scans were collected for each sample using 600-s recycle delays between scans to allow for spin relaxation. Processing included apodization of the data via multiplication by an exponential function that produced 100 Hz of line broadening. Mechanical and thermal characterization. Mechanical properties were determined by uniaxial tensile tests on a dual column Instron 3365 universal testing machine equipped with a 500 N load cell. The tensile measurements were conducted following the indications of ASTM D 882 Standard Test Methods for Tensile Properties of Thin Plastic Sheeting. Dog-bone shaped samples (25 mm length, 4 mm width) were stretched at a rate of 2 mm/min, corresponding to 0.08 min-1 strain rate. All the stress-strain curves were recorded at 25°C and 44% RH. Between seven and ten measurements for each sample were carried out and the results were averaged to obtain a mean value. The values of Young’s modulus, stress and elongation at break were calculated from the stress-strain curves.


Page 9 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The thermal degradation behavior of alginate-cutin samples was investigated by thermogravimetric analysis (TGA) using a Q500 analyzer from TA Instruments. The measurements were carried out under an inert N2 atmosphere on 3 mg samples in an aluminum pan at a heating rate of 10°C/min, from 30 to 600°C. The weight loss (TG curve and its first derivative, DTG curve) was recorded simultaneously as a function of time and temperature. Wettability and hydrodynamic characterization. To characterize the surface wettability of the samples, static water contact angles (W-CA) were measured with the sessile drop method at room temperature and at five different locations on each surface using a contact angle goniometer (DataPhysics OCAH 200). 5 µL droplets of Milli-Q water were deposited on the surfaces and side view images of the drops were captured. W-CAs were automatically calculated by fitting the captured drop shape and after 2 minutes from the drop deposition on the surface in order to consider values at equilibrium. For free-standing films, W-CA measurements were conducted as for any other kind of solid films. For the no-film forming samples, flat regions with areas larger than a water drop were used. For the water uptake characterization, samples were weighed on a sensitive electronic balance (0.0001 g accuracy) and placed in different humidity chambers at 0 and 100% HR. After remaining in humidity chambers for one day, each sample was weighed and the amount of adsorbed water was calculated based on the initial dry weight as the difference. Water vapor permeability. Water vapor permeability (WVP) was determined at 25°C under 100% relative humidity gradient (ΔRH%) according to the ASTM E96 standard method. In this test, permeation chambers with 7 mm inside diameter and 10 mm inner depth were used and filled with 400 μL of deionized water (which generates 100% RH inside the permeation cell)

46

. The samples

were cut into circles and mounted on the top of the permeation chambers. The permeation chambers were placed in a desiccator with anhydrous silica gel, which was used to maintain 0% RH. The water transferred through the film was determined from the weight change of the permeation chamber every -9ACS Paragon Plus Environment


Page 10 of 40

hour during a period of 8 h using an electronic balance (0.0001 g accuracy) to record mass loss over time. The mass loss of the permeation chambers was plotted as a function of time. The slope of each line was calculated by linear regression. Then, the water vapor transmission rate (WVTR) was determined as below 47: 𝑆𝑙𝑜𝑝𝑒

WVTR (g (m2d)-1) = 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒

(1)

WVTR and water vapor permeability (WVP) measurements were replicated three times for each film. The WVP of the sample was then calculated as below: WVP(g (m d Pa)-1) =

𝑊𝑉𝑇𝑅 𝑥 𝐿 𝑥 100 𝑝𝑠 𝑥 𝛥𝑅𝐻

(2)

where L (m) is the thickness of the sample, measured with a micrometer with 0.001 mm accuracy, ΔRH (%) is the percentage relative humidity gradient, and ps (Pa) is the saturation water vapor pressure at 25°C 48-49. Results and Discussion Morphological characterization Photographs of the sodium alginate/tomato pomace monomers (AT) films are shown in Figure 1A. The AT-0 (pure sodium alginate) sample presented a completely transparent surface, as expected for sodium alginate dry material 50. AT-25 and AT-50 films displayed an orange and opaque color due to the presence of tomato pomace monomers in the structure. After the thermal treatment, sodium alginate became yellow. This change of color is related to a partial thermal degradation of the polysaccharide 51. The brown color of AT-25p and AT-50p can be attributed to the polymerization of tomato pomace monomers 16-17. The morphology of AT samples was characterized by scanning electron microscopy (SEM). Figures 1-B, C, D show the cross-sections and top-views of AT-0, AT-25 and AT-50 samples, respectively. -10ACS Paragon Plus Environment

Page 11 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


While the pure sodium alginate film is flat, as the amount of tomato pomace monomers was increased, a larger roughness was observed. On the other hand, Figures 1-E, F, G show the cross-section and top-views of AT-0p, AT-25p and AT-50p, respectively. The pure sodium alginate sample after thermal treatment retained the same flat structure, whereas AT-25p and AT-50p were slightly smoother than their corresponding non-polymerized equivalents, most likely because of the melting of tomato pomace monomers during their thermal treatment.

Figure 1. A, Photographs of sodium alginate/tomato pomace films before and after melting polycondensation. B, C, D, Cross-section SEM images of AT-0, AT-25 and AT-50 samples (nonpolymerized samples), respectively. Insets show the corresponding top-views. E, F, G, Cross-section -11ACS Paragon Plus Environment


Page 12 of 40

SEM images of AT-0p, AT-25p and AT-50p samples (polymerized samples), respectively. Insets show the corresponding top-views. Chemical characterization Direct-polarization solid-state 13C NMR spectra were used to compare the tomato pomace monomers (AT-100), sodium alginate (AT-0), and AT-50 samples both before and after the thermal treatment. The resonances displayed in Figure 2A were relatively broad as observed previously for fruit cutin polymers, likely reflecting spectral superposition of monomers with slightly differing chain lengths and hydroxyl positions 52. Nonetheless, the differences in chemical environment made it possible to distinguish carbonyl, arene/alkene, anomeric sugar, alkoxy, and long-chain methylene structural groups. Whereas the alginate component lacked (CH2)n resonances (25-40 ppm, Figure 2A) and the tomato pomace monomers lacked anomeric sugar signals (101 ppm, Figure 2A), the carbonyl and alkoxy regions included spectral contributions from both constituents. For instance, Figure 2B allowed for identification of an alginate carboxylic acid group at 176 ppm and carboxyls from tomato pomace monomers at 178 and 182 ppm. In the AT-50 sample the carboxyl resonances displayed chemical shifts corresponding to the individual constituents and were partially resolved. Thermal treatment of AT-100 sample ‘replaced’ the carboxyls with resonances at 174 and 176 ppm, suggesting formation of esters as illustrated by the 173-ppm peak observed for lime and tomato cutin polymers 53

. Thermal treatment of the AT-50 sample yielded a broad composite resonance at 176 ppm with

shoulders at 173 and 179 ppm, again suggesting ester formation. Although the 173-ppm signal can be attributed to a cutin-based ester, the 176-ppm resonance could arise from a cutin ester, alginate carboxyl, or intercomponent ester. This latter spectral overlap precludes estimation of the ester percentage in the heat-treated mixture compared with the acid starting material, but the dramatically diminished tomato pomace signal intensities at 178 and 182 ppm suggest ~80% esterification of the tomato pomace monomer carboxyls. The appearance of an ester-like IR band shown in Figure S1 supports this interpretation. Thus, the chemical reaction corresponding to increased hydrophobicity -12ACS Paragon Plus Environment

Page 13 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and brittleness described below is shown to involve the tomato pomace monomer carboxyls and is consistent with the formation of cutin-based esters. Confirmation and extension of these interpretations comes from examination of the alkoxy spectral region highlighted in Figure 2C. The oxymethylene resonances at 63-65 ppm and oxymethine resonances at 72-76 ppm are easily distinguished in this region of the 13C NMR spectrum. Whereas the tomato pomace monomers exhibit 63-ppm CH2OH signals from ω-hydroxyfatty acids and 72-ppm CHOH signals from their mid-chain hydroxy groups, the alginate constituent exhibits a collection of sugar CHO signals resonating between 65 and 76 ppm 54. Thermal treatment of AT-50 and AT-100 samples produced striking 3060% losses in signal intensity for the CH2OH moiety of AT-50p and AT-100p samples, supporting the claim of esterification and strengthening the hypothesis that it involves the tomato pomace monomer constituent. The observation of altered signal intensity primarily for the CH2OH type of alkoxy groups also suggests that esterification of the monomers occurs at the sterically less hindered chain terminus. Finally, we estimated the degrees of esterification and hydrophobic-to-hydrophilic balance of the bio-inspired materials quantitatively by measuring the proportions of each major functional group with respect to the total intensity across the 13C NMR spectrum. We consider only proportions within a given spectrum; quantitative comparisons between the various spectra could be compromised by variations in sample mass, spin relaxation time, and normalization protocols that set the largest peak to full scale. The cleanest assessment of esterification comes from measuring the integrated intensity of the CH2OH group at 62 ppm, which is attributable solely to the tomato pomace monomer constituents. Thermal treatment reduced the contribution of this peak area by 50 and 100% in the AT-50p and AT-100p samples, respectively, confirming the qualitative trends noted above from examination of the peak heights.



Page 14 of 40

Figure 2. A, DPMAS 13C NMR spectra of AT-0, AT-50, AT-50p, AT-100 and AT-100p samples. B, C, D, Expanded NMR spectra respectively in the carboxyl region (160-185 ppm), alkoxy region (57-88 ppm) and long-chain aliphatic region (15-45 ppm). In summary, DPMAS

13

C NMR characterization, supported by ATR-FTIR spectroscopy, indicates

that the thermal treatment induces a partial polymerization between polyhydroxylated and unsaturated fatty acids from tomato pomace with a relatively high degree of esterification (80%), considering that the reaction has not been catalyzed. Moreover, the condensation of –COOH of both types of fatty acids occurs preferably with the primary –OH groups of the polyhydroxylated ones, most probably due to reasons related to steric hindrance. Interestingly, the molecular architecture of natural cutin shows a similar preference with most of primary hydroxyls esterified 10, 55. The situation -14ACS Paragon Plus Environment

Page 15 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is also very similar to those of polymerized tomato cutin monomers and 9,10,16trihydroxyhexadecanoic (or aleuritic) acid by melting polycondensation. In these cases, the degrees of esterification were 15% for cutin monomers and 7% for aleuritic acid, being the esterification mainly through primary hydroxyls and keeping intact most of secondary –OH groups 17, 56. However, unlike them, the participation of unsaturated fatty acids is expected to reduce the chain propagation during polymerization by consuming of hydroxyls without providing additional –OH groups to continue the reaction. Chemical interactions between the polyester and the polysaccharide were characterized by ATRFTIR spectroscopy, Figure 3. Noticeably, shifts in the position of the bands assigned to the O-H and asymmetrical COO- stretching modes were observed, as shown in Figures 3A,B, respectively. The wavenumber of the O-H stretching mode was increased from 3318 cm-1 for AT-0p to 3407 cm-1 for AT-100p, resulting in a shift of 89 cm-1, Figure 3C. This is indicative of an important modification of the H-bonding network when both components are blended. Since the lower wavenumbers are typical of stronger H-bonds 46, the presence of alginate reinforces such a secondary bond network. The shift of the asymmetrical COO- stretching mode was less intense with a difference of 6 cm-1 between 1591 cm-1 for AT-0p to 1597 cm-1 for AT-75p. Such a shift of this band is related to the preferential formation of intermolecular hydrogen bonds of the hydroxyl groups of alginate and other polymers

57

. Finally, a change in the ratio between the intensities of the bands associated with the

C=O stretching modes of free ester groups (1730 cm-1) and ester groups interacting by H-bonds (1715 cm-1) was observed, Figures 3D and S1 14. This ratio was increased from a value of 0.50 for AT-25p to 0.93 for AT-100p, indicating that the population of ester groups interacting by H-bonds was reduced with the presence of alginate. Based on these experimental evidences, we propose a molecular model where the –OH groups of both components present a high affinity to form intermolecular H-bonds between them, partially excluding ester groups of the network, inset of Figure 4D. -15ACS Paragon Plus Environment


Page 16 of 40

Figure 3. A, B, Variation of the O-H and asymmetrical COO- stretching modes, respectively, for different AT samples after the thermal treatment. C, Shift of the O-H (black) and asymmetrical COO(red) stretching modes with the tomato pomace content. D, Ratio ICOOROH/ICOOR as a function of the tomato pomace content. The insets show schematic models at molecular level of samples with low (left) and high (right) tomato pomace content. Mechanical and thermal characterization Typical stress-strain curves of AT samples are shown in Figure 4A. For non-polymerized samples, the mechanical behavior was representative of ductile materials with a characteristic yield point, followed by a plastic deformation, albeit with low values of elongation at fracture, while polymerized films were brittle and broke at lower strain values with no plastic deformation. Values of Young’s modulus and stress and elongation at break are displayed in Figures 4B,C,D, respectively. For non-16ACS Paragon Plus Environment

Page 17 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


polymerized films, the Young’s modulus and stress at break decreased with the proportion of tomato pomace monomers. Indeed, Young’s modulus values were ~1968, ~1338, and ~596 MPa for AT-0, AT-25, and AT-50, respectively, while the stresses at break were ~51, ~25, and ~12 MPa for AT-0, AT-25, and AT-50, respectively. This decrease was relatively lower for the elongation at break with values of ~10, ~6, and ~7 % for AT-0, AT-25, and AT-50, respectively. In general, the mechanical parameters were lower for the thermally treated samples compared to their non-polymerized homologues. Thus, the Young’s modulus shifted slightly to values ~1822, ~1026, and ~615 MPa for AT-0p, AT-25p, and AT-50p, respectively. These reductions were more drastic for the stress (~33, ~6, and ~7 MPa for AT-0p, AT-25p, and AT-50p, respectively) and elongation (~3.0, ~1.6, and ~1.5 % for AT-0p, AT-25p, and AT-50p, respectively) at break. The deterioration of the mechanical properties can be caused by the partial degradation and dehydration of alginate during the thermal treatment 51. In addition, the presence of tomato pomace polyester modifies the H-bonding network of the system, weakening these interactions, and putatively reducing the mechanical properties.



Page 18 of 40

Figure 4. A, Typical stress-strain curves for AT-0 (black solid line), AT-25 (red solid) and AT-50 (blue solid) samples vs. AT-0p (black dashed), AT-25p (red dashed) and AT-50p (blue dashed) samples. B, C, D, Young’s modulus, stress and strain at break parameters, respectively, for AT-0, AT-25 and AT-50 samples before (grey) and after (red) polymerization, calculated from the stressstrain curves. The thermal stability of the samples was evaluated by TGA, shown in Figure 5. Pure tomato pomace fatty monomers (AT-100) exhibited three weight losses at ~30, ~235, and ~415 °C. The first weight loss of ~14% can be associated with the evaporation of free water contained in the monomers. The second event was equivalent to a weight loss of ~37% and is related to the decarboxylation of -18ACS Paragon Plus Environment

Page 19 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydroxyacids and complete degradation of unsaturated fatty acids

17, 22, 58

. The third degradation

(~11% of weight loss) can be attributed to the thermal degradation of hydroxyl groups of hydroxyacids 17. A final residue of ~38% was obtained. On the other hand, two weight loss steps at ~199 (weight loss ~13%) and ~398 °C (weight loss ~82%) were observed for pure sodium alginate (AT-0). The first event is ascribed to the water loss, while the second one to the alginate polymer backbone degradation

59

. A final residue of ~5% was determined. The blends of both components

displayed an intermediate behavior with events associated with tomato pomace monomers and sodium alginate. No significant differences were observed for thermally treated samples containing tomato pomace monomers compared to non-polymerized ones, indicating that the melting polycondensation did not affect their thermal stability or the residual weight, Figure 5B. In the case of AT-0p, the weight loss at ~199 °C disappeared, most probably due to the previous dehydration produced during the thermal treatment at 150 °C for 8 h.



Page 20 of 40

Figure 5. A, B, TGA (top) and the corresponding derivative (bottom) curves of non-polymerized and polymerized samples, respectively. Insets show the final residue as a function of alginate content. Wettability, water uptake and water vapor permeability The analysis of wettability, water uptake and water vapor barrier properties is presented in Figure 6. Static water contact angles are shown in Figure 6A. The hydrophobicity depended on the relative proportion of both components. Thus, as expected, the pure sodium alginate sample was the most hydrophilic material with a W-CA of 43°, close to the value reported elsewhere

60

. The

hydrophobicity increased with the proportion of tomato pomace monomers, attaining W-CA values of 77, 81, 101, and 110° for AT-25, AT-50, AT-75, and AT-100, respectively. After the thermal treatment in oven, samples showed higher contact angle values with a similar trend to the nonpolymerized equivalents. In the case of pure sodium alginate, the W-CA was increased to 72°. This phenomenon is related to the degradation reaction during the thermal treatment that can reduce the number of polar groups on the surface 51. The W-CA values for AT-25p, AT-50p, AT-75p, and AT100p were 92, 96, 109, and 118°, respectively. The condensation of –COOH and –OH functional groups to produce less polar ester groups can account for the increase of hydrophobicity compared to non-polymerized samples. The water uptake of AT samples decreased linearly with the tomato pomace monomer content, as shown in Figure 6B. In particular, it was reduced from 54% for AT-0 to 7% for AT-100 and from 47% for AT-0p to 6% for AT-100p. Similarly to the wettability, the water uptake trends can be explained by the hydrophobic behavior of tomato pomace fatty monomers and the reduced presence of polar groups after the thermal treatment. Regarding water barrier properties, the water vapor transmission rate (WVTR) and water vapor permeability (WVP) values are displayed in Figures 6C and 6D, respectively. Both parameters decreased with the proportion of tomato pomace monomers because of the hydrophobic character of -20ACS Paragon Plus Environment

Page 21 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


long-chain polyhydroxylated and unsaturated fatty acids from tomato pomace. The condensation of these fatty acids produced an additional decrease in water barrier properties due to, as mentioned above, the disappearance of polar hydroxyl and carboxyl groups and the formation of esters. For WVTR, the values for non-polymerized films ranged between ~9326 g m-2 d-1 for AT-0 to ~7643 g m-2 d-1 for AT-50 (a reduction of ca. 19%), while the parameters for the polymerized samples were ~8500 g m-2 d-1 for AT-0p and ~6300 g m-2 d-1 for AT-50p (a reduction of ca. 26%). A similar tendency was observed for WVP, with values of ~1.65 g m-1 d-1 Pa-1 for AT-0 and ~1.28 g m-1 d-1 Pa1

for AT-50 (a reduction of ca. 25%) and ~1.42 g m-1 d-1 Pa-1 for AT-0p and ~1.13 g m-1 d-1 Pa-1 for

AT-50p (a reduction of ca. 24%).

Figure 6. A, B, C, D, Water contact angle (W-CA), water uptake values, water vapor transmission rate (WVTR), and water vapor permeability (WVP), respectively, for non-polymerized (red) and polymerized (black) samples as a function of the tomato pomace monomer content. -21ACS Paragon Plus Environment


Page 22 of 40

Effect of beeswax on mechanical and hydrodynamic properties Beeswax was added in different percentages (0, 5, 15, and 30 wt.%) to the AT-50p sample to study its effect on morphological, mechanical, and hydrodynamic properties. The results are displayed in Figures 7 and 8. Figures 7A,B,C present pictures and SEM cross-section images of AT-50p sample containing 5, 15, and 30 wt.% of beeswax (labeled as B-5, B-15, and B-30, respectively). While their macroscopic appearances were very similar, though slightly clearer as the amount of beeswax increased due to the yellow color of the wax 61, the cross-section images revealed some differences. For instance, B-5 presented a morphology similar to AT-50p, whereas in the B-30 film a more compact and homogeneous structure was observed. A higher presence of liquid material (i.e., beeswax and tomato pomace monomers in the melted state) during the thermal treatment can produce this modification. Smoother surfaces of beeswax-rich samples were also observed in the top-views, as shown in Figure S2. Figure 7D shows the tensile test curves of AT-50p samples with beeswax. The addition of the wax resulted in an enhancement in mechanical parameters. The Young’s modulus increased from 615 MPa for B-0 to 1025 MPa for B-5 and B-15 and 1075 MPa for B-30, Figure 7E. Stress at break values were also increased from 7 MPa for B-0 to 18 MPa for B-5, 21 MPa for B-15, and 24 MPa for B-30 films. Even the elongation at break was improved, with values ranging from 1.5% for B-0 to 2% for B-5, 2.5% for B-15, and 3% for B-30 samples. The reinforcement effect of beeswax can be explained by a lower tendency of the samples to lose water (as shown below) and a greater rigidity induced by the interaction between the waxes and the tomato pomace fatty fraction after the thermal treatment. In fact, intracuticular waxes have been reported to increase Young’s modulus and stress at break in natural plant cuticles 62.


Page 23 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. A, B, C, Cross-section SEM images of B-5, B-15 and B-30 samples. Insets are the corresponding photos. D, Typical stress-strain curves for AT-50p sample with different relative contents (%) of beeswax: B-0 (blue), B-5 (red), B-15 (light blue) and B-30 (light green). E, F, Young’s modulus, stress at break (black) and elongation at break (red) values for B-0, B-5, B-15 and B-30 samples, respectively. -23ACS Paragon Plus Environment


Page 24 of 40

Changes in the hydrodynamic properties after the addition of beeswax are shown in Figure 8. As expected, the hydrophobicity of the films increased with the beeswax content, Figure 8A. The sample without wax, B-0, presented a W-CA of 96,° whereas for B-5, B-15 and B-30 W-CA values were 102°, 104° and 106°, respectively. The variation in water uptake with the proportion of beeswax is presented in Figure 8B. Water uptake values decreased from 32% for B-0 to 24% for the B-5 sample, 21% for B-15, and 17% for B-30. Finally, water vapor barrier properties were also determined, Figure 8C. WVTR and WPV values were lower when beeswax was added. Values of WVTR and WVP were reduced by 70% and 54%, respectively, from 6305 g m-2 d-1 and 1.1 × 10-4 g m-1 d-1 Pa-1 for B-0 to 1847 g m-2 d-1 and 4.7 × 10-5 g m-1 d-1 Pa-1 for B-30 samples. B-5 and B-15 showed intermediate values. WVTR values of B-30 were comparable to those of other materials such as cellulose acetate (2920 g m-2 d-1), cellulose acetate propionate (1700 g m-2 d-1), cellulosepolyaleuritate-carnauba wax composite (2550 g m-2 d-1), and thermal treated protein-starch blends (~1850 g m-2 d-1) 63-66. On the other hand, WVP values were similar to those reported for starch from cassava (1.01 × 10-5 g m-1 d-1 Pa-1), soy protein (1.05 × 10-4 g m-1 d-1 Pa-1), and cellophane (7.26 × 10-6 g m-1 d-1 Pa-1) 67.


Page 25 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8.


A, B, C, Water contact angle, water uptake, and water vapor barrier properties,

respectively, of B-0, B-5, B-15 and B-30 samples. To finish, a model for the interaction between beeswax, tomato pomace polyester, and alginate is proposed. Considering that the polyester and the polysaccharide interacts through intermolecular H-25ACS Paragon Plus Environment


Page 26 of 40

bonds between their hydroxyl groups with practically no participation of ester groups, as discussed during ATR-FTIR characterization above, it is expected that the interaction between beeswax (71% wax esters) and alginate is low. On the other hand, as described for natural cuticles 68, hydrophobic interactions can be favored for tomato pomace polyester and beeswax due to the attractive van der Waals forces between aliphatic chains. This model with the polyester as a matrix that can specifically interacts with alginate and beeswax is similar to those proposed for natural plant cuticles where cutin can make compatible polysaccharides from the cell wall and cuticle waxes 52. Conclusions In this work, we present a sustainable procedure for the fabrication of composite free-standing films inspired by plant cuticles. It consists of the blending in green solvents (ethanol and water) of sodium alginate, unsaturated and polyhydroxylated fatty acids derived from the agro-waste of the tomato peeling industrial process, with a beeswax additive and subsequent thermal treatment. The chemical structure was characterized by solid-state NMR and FT-IR spectroscopy, showing that the thermal process induced the condensation of the fatty acids and that the tomato pomace polyester can specifically interacts with alginate and beeswax by H-bonds and van der Waals forces, respectively. The mechanical properties depended significantly on the tomato pomace monomer content and the water loss produced by the thermal treatment. No significant differences in thermal stability were detected for polymerized and non-polymerized samples. Water contact angle, uptake, and barrier properties were improved with the proportion of tomato pomace monomers and the thermal treatment because of the intrinsic hydrophobicity of unsaturated and polyhydroxylated fatty acids as well as the lower presence of polar hydroxyl and carboxyl functional groups after the melt-polycondensation. Furthermore, the addition of beeswax to AT-50p improved both mechanical (by reinforcement of the structure) and hydrodynamic (due to the high hydrophobicity of the waxes) properties. Despite a more exhaustive comparison with commercially available bio-based and biodegradable packaging films is


Page 27 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


necessary, these plant cuticle-like films can be considered potential alternatives for the design and production of sustainable composite materials to traditional plastics used in packaging applications. Acknowledgements The authors would like to thank Mrs. Lara Marini for her assistance with the thermal measurements.

Supporting Information Comparison in the infrared spectral region of the C=O stretching mode (1775–1675 cm−1) for AT-50 vs. AT-50p and AT-100 vs. AT-100p samples (Figure S1); Top-view SEM images of B-5, B-15 and B-30 samples (Figure S2).

References (1) PlasticEurope. Plastics - The fact. 2017. (2) Heredia-Guerrero, J. A.; Athanassiou, A. Editorial: Non-polysaccharide Plant Polymeric Materials. Frontiers in Materials 2016, 3, DOI: 10.3389/fmats.2016.00015. (3) Mülhaupt, R. Green Polymer Chemistry and Bio-based Plastics: Dreams and Reality. Macromolecular Chemistry and Physics 2013, 214 (2), 159-174, DOI: 10.1002/macp.201200439. (4) Robinson, P. Petroleum Processing Overview, 2007; Vol. 1, p 1-78. (5) Siddique, R.; Khatib, J.; Kaur, I. Use of recycled plastic in concrete: a review. Waste management 2008, 28 (10), 1835-52, DOI: 10.1016/j.wasman.2007.09.011. (6) Geyer, J., Law. Production, use, and fate of all plastics ever made. Sci. Adv. 2017, 3 (7), DOI: 10.1126/sciadv.1700782. (7) Tokiwa, Y.; Calabia, B. P.; Ugwu, C. U.; Aiba, S. Biodegradability of plastics. International journal of molecular sciences 2009, 10 (9), 3722-42, DOI: 10.3390/ijms10093722. (8) Sudesh, K.; Iwata, T. Sustainability of Biobased and Biodegradable Plastics. CLEAN – Soil, Air, Water 2008, 36 (5‐6), 433-442, DOI: doi:10.1002/clen.200700183. (9) Bensaude-Vincent, B. Reconfiguring Nature Through Syntheses: From Plastics to Biomimetics. MIT Press 2007, 293-312. (10) Heredia, A. Biophysical and biochemical characteristics of cutin, a plant barrier biopolymer. Biochimica et Biophysica Acta (BBA) - General Subjects 2003, 1620 (1-3), 1-7, DOI: 10.1016/s0304-4165(02)00510-x. (11) Domínguez, E.; Heredia-Guerrero, J. A.; Heredia, A. The biophysical design of plant cuticles: an overview. New Phytologist 2011, 189 (4), 938-949, DOI: 10.1111/j.1469-8137.2010.03553.x. (12) Heredia-Guerrero, J. A., Guzman-Puyol, S., Benitez, J., J., Athanassiou, A., Heredia, A., Dominguez, E. Plant cuticle under global change: Biophysical Implications. Glob Change Biol. 2018, 24, 2749-2751, DOI: 10.1111/gcb.14276. (13) Zhang, B.-x.; Uyama, H. Biomimic Plant Cuticle from Hyperbranched Poly(ricinoleic acid) and Cellulose Film. ACS Sustainable Chemistry & Engineering 2015, 4 (1), 363-369, DOI: 10.1021/acssuschemeng.5b01392.



Page 28 of 40

(14) Heredia-Guerrero, J. A.; Benitez, J. J.; Dominguez, E.; Bayer, I. S.; Cingolani, R.; Athanassiou, A.; Heredia, A. Infrared and Raman spectroscopic features of plant cuticles: a review. Frontiers in plant science 2014, 5, 305, DOI: 10.3389/fpls.2014.00305. (15) Kershaw, P. Exploring the potential for adopting alternative materials to reduce marine plastic litter. UN environment. (16) Heredia-Guerrero, J. A.; Heredia, A.; García-Segura, R.; Benítez, J. J. Synthesis and characterization of a plant cutin mimetic polymer. Polymer 2009, 50 (24), 5633-5637, DOI: 10.1016/j.polymer.2009.10.018. (17) Benítez, J. J.; Heredia-Guerrero, J. A.; Guzmán-Puyol, S.; Barthel, M. J.; Domínguez, E.; Heredia, A. Polyhydroxyester Films Obtained by Non-Catalyzed Melt-Polycondensation of Natural Occurring Fatty Polyhydroxyacids. Frontiers in Materials 2015, 2 (59), DOI: 10.3389/fmats.2015.00059. (18) Manrich, A.; Moreira, F. K.; Otoni, C. G.; Lorevice, M. V.; Martins, M. A.; Mattoso, L. H. Hydrophobic edible films made up of tomato cutin and pectin. Carbohydrate polymers 2017, 164, 83-91, DOI: 10.1016/j.carbpol.2017.01.075. (19) Petracek, P., D., Bukovac, M., J. Rheological properties of enzymatically isolatedtomato fruit cuticle. Plant Physiology 1995, 109, 675-679, DOI: 10.1104/pp.109.2.675. (20) Matas., A., J., Cuartero, J., Heredia, A. Phase transitions in the biopolyester cutin isolated from tomato fruit cuticles. Thermochimica Acta 2004, 409, 165-168, DOI: 10.1016/S0040-6031(03)00357-5. (21) Philippe, G., Gaillard, C., Petit, J. Ester cross-link profiling of the cutin polymer of wild-type and cutin synthase tomato mutants highlights different mechanisms of polymerization. Plant Physiology 2016, 170, 807-820, DOI: 10.1104/pp.15.01620. (22) Benitez, J. J., Heredia-Guerrero, J., A., Bayer, I., S., Athanassiou, A. A polyester from tomato fruit processing residues obtained by non-catalyzed melt-polycondensation in air. Patent Number: ES201630194 2016. (23) Cigognini, I., Montanari, A., de la Torre Carreras, r., Cardoso B., M., G. Extraction method of a polyester polymer or cutin from the wasted tomato pomaces and polyester polymer so extracted. WO2015028299 A1 2015. (24) Heredia-Guerrero, J. A.; Heredia, A.; Dominguez, E.; Cingolani, R.; Bayer, I. S.; Athanassiou, A.; Benitez, J. J. Cutin from agro-waste as a raw material for the production of bioplastics. Journal of experimental botany 2017, 68 (19), 5401-5410, DOI: 10.1093/jxb/erx272. (25) Del Valle, M.; Cámara, M.; Torija, M.-E. Chemical characterization of tomato pomace. Journal of the Science of Food and Agriculture 2006, 86 (8), 1232-1236, DOI: 10.1002/jsfa.2474. (26) Philippe, G.; Gaillard, C.; Petit, J.; Geneix, N.; Dalgalarrondo, M.; Bres, C.; Mauxion, J. P.; Franke, R.; Rothan, C.; Schreiber, L.; Marion, D.; Bakan, B. Ester Cross-Link Profiling of the Cutin Polymer of Wild-Type and Cutin Synthase Tomato Mutants Highlights Different Mechanisms of Polymerization. Plant Physiol 2016, 170 (2), 807-20, DOI: 10.1104/pp.15.01620. (27) Cámara, M., Del Valle, M., Torija, M., E., Castilho, C. Fatty Acid Composition of Tomato Pomace. Acta Hortic. 2001, 542, 175-180, DOI: 10.17660/ActaHortic.2001.542.21. (28) Drummond, D. W., Hirst, E. L., Percival, E. The Constitution of Alginic Acid. J. Chem. Soc. 1962, 0, 12081216, DOI: 10.1039/JR9620001208. (29) Liakos, I.; Rizzello, L.; Scurr, D. J.; Pompa, P. P.; Bayer, I. S.; Athanassiou, A. All-natural composite wound dressing films of essential oils encapsulated in sodium alginate with antimicrobial properties. International journal of pharmaceutics 2014, 463 (2), 137-45, DOI: 10.1016/j.ijpharm.2013.10.046. (30) Yang, L.; Guo, J.; Wu, J.; Yang, Y.; Zhang, S.; Song, J.; An, Q.; Gong, Y. Preparation and properties of a thin membrane based on sodium alginate grafting acrylonitrile. RSC Adv. 2017, 7 (80), 50626-50633, DOI: 10.1039/c7ra08532j. (31) Sood, A.; Arora, V.; Shah, J.; Kotnala, R. K.; Jain, T. K. Multifunctional gold coated iron oxide core-shell nanoparticles stabilized using thiolated sodium alginate for biomedical applications. Materials science & engineering. C, Materials for biological applications 2017, 80, 274-281, DOI: 10.1016/j.msec.2017.05.079. (32) Lee, K. Y.; Mooney, D. J. Alginate: properties and biomedical applications. Prog Polym Sci 2012, 37 (1), 106-126, DOI: 10.1016/j.progpolymsci.2011.06.003.


Page 29 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Wang, L.; Shelton, R. M.; Cooper, P. R.; Lawson, M.; Triffitt, J. T.; Barralet, J. E. Evaluation of sodium alginate for bone marrow cell tissue engineering. Biomaterials 2003, 24 (20), 3475-3481, DOI: 10.1016/s0142-9612(03)00167-4. (34) Galus, S.; Lenart, A. Development and characterization of composite edible films based on sodium alginate and pectin. Journal of Food Engineering 2013, 115 (4), 459-465, DOI: 10.1016/j.jfoodeng.2012.03.006. (35) Olivas, G. I.; Barbosa-Cánovas, G. V. Alginate–calcium films: Water vapor permeability and mechanical properties as affected by plasticizer and relative humidity. LWT - Food Science and Technology 2008, 41 (2), 359-366, DOI: 10.1016/j.lwt.2007.02.015. (36) Pranoto, Y.; Salokhe, V. M.; Rakshit, S. K. Physical and antibacte rial properties of alginate-based edible film incorporated with garlic oil. Food Research International 2005, 38 (3), 267-272, DOI: 10.1016/j.foodres.2004.04.009. (37) Rhim, J.-W. Physical and mechanical properties of water resistant sodium alginate films. LWT - Food Science and Technology 2004, 37 (3), 323-330, DOI: 10.1016/j.lwt.2003.09.008. (38) Rinaudo, M. Biomaterials based on a natural polysaccharide: alginate. Tip 2014, 17 (1), 92-96, DOI: 10.1016/s1405-888x(14)70322-5. (39) Tolluch, A., P. The Composition of Beeswax and Other Waxes Secreted by Insects. Lipids 1970, 5 (2), 247258, DOI: 10.1007/BF02532476. (40) Donhowe, I., G., Fennema, O. Water Vapor and Oxygen Permeability of Wax Films. JAOCS 1993, 70 (9), 867-873, DOI: 10.1007/BF02545345. (41) Talens, P., Krochta, J., M. Plasticizing Effects of Beeswax and Carnauba Wax on Tensile and Water Vapor Permeability Properties of Whey Protein Films. Journal of Food Science 2005, 70 (3), 239-243, DOI: 10.1111/j.1365-2621.2005.tb07141.x (42) Byrne, F. P.; Jin, S.; Paggiola, G.; Petchey, T. H. M.; Clark, J. H.; Farmer, T. J.; Hunt, A. J.; Robert McElroy, C.; Sherwood, J. Tools and techniques for solvent selection: green solvent selection guides. Sustainable Chemical Processes 2016, 4 (1), DOI: 10.1186/s40508-016-0051-z. (43) Benítez, J. J.; Heredia-Guerrero, J. A.; de Vargas-Parody, M. I.; Cruz-Carrillo, M. A.; Morales-Flórez, V.; de la Rosa-Fox, N.; Heredia, A. Biodegradable polyester films from renewable aleuritic acid: surface modifications induced by melt-polycondensation in air. Journal of Physics D: Applied Physics 2016, 49 (17), 175601, DOI: 10.1088/0022-3727/49/17/175601. (44) Hahn, E., L. Spin Echoes. Physical Review 1950, 80, 580-59, DOI: 10.1103/PhysRev.80.580. (45) Bennet, A., E., Rienstra, C., M., Auger, M., Lakshmi, K., V., Griffin, R., G. Heteronuclear decoupling in rotating solids. J. Chem. Phys. 1995, 103, 6951-6958, DOI: 10.1063/1.470372. (46) Tran, T. N.; Paul, U.; Heredia-Guerrero, J. A.; Liakos, I.; Marras, S.; Scarpellini, A.; Ayadi, F.; Athanassiou, A.; Bayer, I. S. Transparent and flexible amorphous cellulose-acrylic hybrids. Chemical Engineering Journal 2016, 287, 196-204, DOI: 10.1016/j.cej.2015.10.114. (47) Gennadios, A., Weller, L., C. & Gooding, C., H. Measurement Errors in Water Vapor Permeability of Highly Permeable, Hydrophilic Edible Films. Journal of Food Engineering 1994, 21, 395-409, DOI: 10.1016/02608774(94)90062-0. (48) Ho, T. T.; Zimmermann, T.; Ohr, S.; Caseri, W. R. Composites of cationic nanofibrillated cellulose and layered silicates: water vapor barrier and mechanical properties. ACS applied materials & interfaces 2012, 4 (9), 4832-40, DOI: 10.1021/am3011737. (49) Rhim, J.-W. Effect of clay contents on mechanical and water vapor barrier properties of agar-based nanocomposite films. Carbohydrate polymers 2011, 86 (2), 691-699, DOI: 10.1016/j.carbpol.2011.05.010. (50) Pereira, R.; Mendes, A.; Bártolo, P. Alginate/Aloe Vera Hydrogel Films for Biomedical Applications. Procedia CIRP 2013, 5, 210-215, DOI: 10.1016/j.procir.2013.01.042. (51) Soazo, M.; Báez, G.; Barboza, A.; Busti, P. A.; Rubiolo, A.; Verdini, R.; Delorenzi, N. J. Heat treatment of calcium alginate films obtained by ultrasonic atomizing: Physicochemical characterization. Food Hydrocolloids 2015, 51, 193-199, DOI: 10.1016/j.foodhyd.2015.04.037. (52) Chatterjee, S.; Matas, A. J.; Isaacson, T.; Kehlet, C.; Rose, J. K.; Stark, R. E. Solid-State (13)C NMR Delineates the Architectural Design of Biopolymers in Native and Genetically Altered Tomato Fruit Cuticles. Biomacromolecules 2016, 17 (1), 215-24, DOI: 10.1021/acs.biomac.5b01321.



Page 30 of 40

(53) Zlotnik-Mazori, T., Stark., R., E. Nuclear Magnetic Resonance Studies of Cutin, an Insoluble Plant Polyester. Macromolecules 1988, 21 (8), 2412-2417, DOI: 10.1021/ma00186a019. (54) Sperger, D. M.; Fu, S.; Block, L. H.; Munson, E. J. Analysis of composition, molecular weight, and water content variations in sodium alginate using solid-state NMR spectroscopy. Journal of pharmaceutical sciences 2011, 100 (8), 3441-3452, DOI: 10.1002/jps.22559. (55) Fang, X.; Qiu, F.; Yan, B.; Wang, H.; Mort, A. J.; Stark, R. E. NMR studies of molecular structure in fruit cuticle polyesters. Phytochemistry 2001, 57 (6), 1035-1042, DOI: https://doi.org/10.1016/S00319422(01)00106-6. (56) Benítez, J. J.; Heredia‐Guerrero, J. A.; Guzmán‐Puyol, S.; Domínguez, E.; Heredia, A. Polyester films obtained by noncatalyzed melt‐condensation polymerization of aleuritic (9,10,16‐trihydroxyhexadecanoic) acid in air. Journal of Applied Polymer Science 2015, 132 (4), DOI: doi:10.1002/app.41328. (57) Hajiali, H.; Heredia-Guerrero, J. A.; Liakos, I.; Athanassiou, A.; Mele, E. Alginate Nanofibrous Mats with Adjustable Degradation Rate for Regenerative Medicine. Biomacromolecules 2015, 16 (3), 936-943, DOI: 10.1021/bm501834m. (58) Garcia-Zapateiro, L., A., Franco, J., M., Valencia, C., Delgado, M., A., Gallegos, C. Viscous, thermal and tribological characterization of oleic and ricinoleic acids-derived estolides and their blends with vegetable oils. Journal of Industrial and Engineering Chemistry 2013, 19, 1289-1298, DOI: 10.1016/j.jiec.2012.12.030. (59) Soares, J., P., Santos, J., E., Chierice, G., O., Cavalheiro, E., T., G. Thermal behavior of alginic acid and its sodium salt. Eclet. Quim. 2004, 29 (2), DOI: 10.1590/S0100-46702004000200009 (60) Aljohani, W., Ullah, M.W., Li, W. et al. Three-dimensional printing of alginate-gelatin-agar scaffolds using free-form motor assisted microsyringe extrusion system. J Polym Res 2018, 25, 62, DOI: 10.1007/s10965-0181455-0. (61) Hossain, M., E., Ketata, C., Mann, H., Islam, M., R. Sem-based structural and chemical analysis of paraffin wax and beeswax for petroleum applications. JCDNM 2009, 1 (1), 21-38. (62) Khanal, B., P., Grimm, E., Finger, S., Blume, A., Knoche, M. Intracuticular wax fixes and restricts strain in leaf and fruit cuticles. New Phytologist 2013, 200 (1), 134-43, DOI: 10.1111/nph.12355. (63) Sprockel, O., L., Prapaitrakul, W., Shivanand, P.,. Permeability of Cellulose Polymers: Water Vapour Transmission Rates. Journal of Pharmacy and Pharmacology 1990, 42 (3), 152-157, DOI: 10.1111/j.20427158.1990.tb05375.x (64) Heredia-Guerrero, J. A.; Benítez, J. J.; Cataldi, P.; Paul, U. C.; Contardi, M.; Cingolani, R.; Bayer, I. S.; Heredia, A.; Athanassiou, A. All-Natural Sustainable Packaging Materials Inspired by Plant Cuticles. Advanced Sustainable Systems 2017, 1 (1-2), 1600024, DOI: 10.1002/adsu.201600024. (65) Tedeschi, G.; Guzman-Puyol, S.; Paul, U. C.; Barthel, M. J.; Goldoni, L.; Caputo, G.; Ceseracciu, L.; Athanassiou, A.; Heredia-Guerrero, J. A. Thermoplastic cellulose acetate oleate films with high barrier properties and ductile behaviour. Chemical Engineering Journal 2018, 348, 840-849, DOI: 10.1016/j.cej.2018.05.031. (66) Jagannath, J., H., Nanjappa, C., Das Gupta, D., K., Bawa, A., S. Mechanical and Barrier Properties of Edible Starch-Protein-Based Films. Journal of Applied Polymer Science 2003, 88, 64-71, DOI: 10.1002/app.11602 (67) Gutiérrez, T. J., Polymers for Food Applications. Springer: 2018. (68) Lara, I.; Belge, B.; Goulao, L. F. A Focus on the Biosynthesis and Composition of Cuticle in Fruits. Journal of Agricultural and Food Chemistry 2015, 63 (16), 4005-4019, DOI: 10.1021/acs.jafc.5b00013.


Page 31 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphical abstract

Synopsis Plant cuticle-like bioplastics were prepared through a sustainable process by blending tomato pomace fatty acids, alginate and beeswax.



Figure 1. A, Photographs of sodium alginate/tomato pomace films before and after melting polycondensation. B, C, D, Cross-section SEM images of AT-0, AT-25 and AT-50 samples (non-polymerized samples), respectively. Insets show the corresponding top-views. E, F, G, Cross-section SEM images of AT0p, AT-25p and AT-50p samples (polymerized samples), respectively. Insets show the corresponding topviews. 154x131mm (300 x 300 DPI)

ACS Paragon Plus Environment

Page 32 of 40

Page 33 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. A, DPMAS 13C NMR spectra of AT-0, AT-50, AT-50p, AT-100 and AT-100p samples. B, C, D, Expanded NMR spectra respectively in the carboxyl region (160-185 ppm), alkoxy region (57-88 ppm) and long-chain aliphatic region (15-45 ppm). 144x119mm (300 x 300 DPI)



Figure 3. A, B, Variation of the O-H and asymmetrical COO- stretching modes, respectively, for different AT samples after the thermal treatment. C, Shift of the O-H (black) and asymmetrical COO- (red) stretching modes with the tomato pomace content. D, Ratio ICOOR⋅⋅⋅OH/ICOOR as a function of the tomato pomace content. The insets show schematic models at molecular level of samples with low (left) and high (right) tomato pomace content. 150x114mm (300 x 300 DPI)


Page 34 of 40

Page 35 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. A, Typical stress-strain curves for AT-0 (black solid line), AT-25 (red solid) and AT-50 (blue solid) samples vs. AT-0p (black dashed), AT-25p (red dashed) and AT-50p (blue dashed) samples. B, C, D, Young’s modulus, stress and strain at break parameters, respectively, for AT-0, AT-25 and AT-50 samples before (grey) and after (red) polymerization, calculated from the stress-strain curves. 161x142mm (300 x 300 DPI)



Figure 5. A, B, TGA (top) and the corresponding derivative (bottom) curves of non-polymerized and polymerized samples, respectively. Insets show the final residue as a function of alginate content. 130x85mm (300 x 300 DPI)


Page 36 of 40

Page 37 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. A, B, C, D, Water contact angle (W-CA), water uptake values, water vapor transmission rate (WVTR), and water vapor permeability (WVP), respectively, for non-polymerized (red) and polymerized (black) samples as a function of the tomato pomace monomer content. 140x99mm (300 x 300 DPI)



Figure 7. A, B, C, Cross-section SEM images of B-5, B-15 and B-30 samples. Insets are the corresponding photos. D, Typical stress-strain curves for AT-50p sample with different relative contents (%) of beeswax: B-0 (blue), B-5 (red), B-15 (light blue) and B-30 (light green). E, F, Young’s modulus, stress at break (black) and elongation at break (red) values for B-0, B-5, B-15 and B-30 samples, respectively. 221x247mm (300 x 300 DPI)


Page 38 of 40

Page 39 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. A, B, C, Water contact angle, water uptake, and water vapor barrier properties, respectively, of B0, B-5, B-15 and B-30 samples. 200x340mm (300 x 300 DPI)



Graphical abstract 46x25mm (300 x 300 DPI)


Page 40 of 40

Sustainable fabrication of plant cuticle-like packaging films from

Recommend Documents