Cellulose-Lignin Biodegradable and Flexible UV Protection Film

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Cellulose-Lignin Biodegradable and Flexible UV Protection Film Hasan Sadeghifar, Richard A. Venditti, Jesse S. Jur, Russell E. Gorga, and Joel J Pawlak ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02003 • Publication Date (Web): 10 Nov 2016 Downloaded from http://pubs.acs.org on November 13, 2016

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ACS Sustainable Chemistry & Engineering

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Cellulose-Lignin Biodegradable and Flexible UV Protection Film Hasan Sadeghifar1,2, Richard Venditti1*, JesseJur3, Russell E. Gorga3, Joel J. Pawlak1 1 2

Department of Forest Biomaterials, North Carolina State University, Raleigh, North Carolina 27695, United States Department of Wood and Paper Science, Sari Branch, Islamic Azad University, P.O. Box 48161-19318, Sari, Iran 3 Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, North Carolina 27695, United States

CorrespondingAuthor: Richard Venditti: E-mail: [email protected]

ABSTRACT

There is significant interest in biodegradable and transparent UV protection films from renewable resources for many different applications. Herein, the preparation and characterization of semi-transparent flexible cellulose films containing low amounts of covalently bonded lignin with UV blocking properties are described. Azide modified cellulose dissolved in dimethylacetamide/lithium chloride (DMAc/LiCl) was reacted with propargylated lignin to produce 0.5, 1 and 2% by weight lignin containing materials. Cellulose-lignin films were prepared by regeneration in acetone. These covalently bonded cellulose-lignin films were homogeneous, unlike the simple blends of cellulose and lignin. Prepared films showed high UV protection ability. Cellulose film containing 2% lignin showed 100% protection of UV-B (280320 nm) and more than 90% of UV-A (320-400 nm). The UV protection of prepared films was persistent when exposed to thermal treatment at 120 °C and UV irradiation. Thermogravimetric analysis showed the films to have minimal mass loss up to 275 °C. Thermal expansion of the film was measured with an x-ray diffraction (XRD) method to be around α = 5.2 x 10-5C-1. The tensile strength of the neat cellulose film was around 120 MPa with about a 10% strain to break. Treated cellulose films with 2% lignin showed lower tensile strength (90 MPa). The described methods demonstrate a straightforward procedure to produce renewable based cellulose-lignin UV light blocking films.

KEYWORDS: UV protection, cellulose, lignin, click chemistry, transparent film, flexible film

ACS Paragon Plus Environment


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2 INTRODUCTION Excessive exposure to sunlight increases biological damage and degradation of organic compounds by UVA (320–400 nm) and UVB (280–320 nm) radiation1. UV radiation is responsible for the

discoloration of dyes and pigments, weathering, yellowing of plastics, papers, loss of mechanical properties (cracking), sun burnt skin and other problems associated with UV light. Paints, plastics, wood and cosmetic manufacturers have a great interest in offering products that remain unaltered for long periods of time under severe light exposure conditions2,3. UV absorbers have been used in order to reduce these damaging effects to achieve a good conservation of the properties of the materials. Almost all UV absorbers are synthetic materials. The active ingredients in sunscreens are often synthetic chemicals. Long-time use of such chemicals may cause unexpected side effects and thus are receiving significant attention recently. Natural products such as green coffee oil, extracts of carica papaya, rosakordesiihave been shown to have radiation protection functions4,5. Many natural sunscreens also have good antioxidant properties. However, most of the natural products are part-spectrum sun blockers and cannot block the full spectrum of UV light. In addition, the extraction of the active ingredients from raw materials can be expensive. Cellulose, the most abundant natural polymer in nature, is renewable, biodegradable, and biocompatible. Production of renewable, flexible and transparent film from native cellulose has been reported6-8. Direct dissolution of native cellulose has been studied extensively and a variety of solvent systems is known9. The DMAc/LiCl system is effective native cellulose solvent, first described in 197910, and has been frequently used. Native cellulose offers great opportunities in the fields of edible materials, packaging, electronics, and medical devices and as a substrate film for different applications. It is a promising environmental solution to the plastic waste issue. Moreover, a series of regenerated cellulose products such as novel cellulose fibers, functional fibers, separation membrane materials and aerogels have been fabricated successfully from native cellulose film 6,8,11,12. Cellulose film has a much lower coefficient of thermal expansion (CTE) compared to plastic substrates. Cellulose materials can also tolerate a much higher processing temperature than many plastics. The high transparency and flexibility of cellulosic film allows it to replace plastic substrates in a wide range of applications. Various electronic devices have been successfully demonstrated on plastic substrates (PET, PEM, PC, and PI) including transistor backplanes, thin


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film transistors, organic light emitting diodes, UV protection films and others. Challenges remain with plastic substrates, including a low processing temperature, a large coefficient of thermal expansion (CTE), and poor printability and recyclability, potential properties in which cellulose based materials may offer advantage. Developing a new generation of self-protective sunscreen products such as visually transparent UV filters is important due to disadvantages of petroleum-basedpolymers13. Development of cellulose films containing UV absorbers has many potential applications, such as outdoor UVsensitive polymers, car windshields, clean windows, contact lenses, and some special biological test containers. Preparation of cotton fabrics modified with ZnO nanorods on the surface resulted in UV-blocking in the range of 400–280 nm14,15. Also, nanocellulose based films with firm and uniform networks, excellent optical transparency and high temperature stability in blends with ZnO were reported as UV blockers16. Lignin is the only component in lignocellulosic plant materials rich in aromatic rings due to its basic phenylpropane unit17. It also contains UV absorbing functional groups such as phenolic units, ketones and other chromophores18. Chromophores in the lignin structure make it a natural broad-spectrum sun blocker19. In addition to the UV absorption property, the free radical scavenging ability of phenolic groups gives lignin an excellent antioxidant property and can increase thermal and oxidation stability of polymers in blends2,18,20. However, lignin is a branched phenolic polymer and not compatible with carbohydrate polymers like cellulose. To make effective composites of other natural polymers with lignin, it is sometimes necessary to connect the polymers with a covalent bond. In this study, cellulose based transparent films containing 0.5 to 2% covalently bonded lignin was generated. Cellulose modified with azide functional groups was dissolved in DMAc/LiCL and reacted with lignin containing propargyl groups using click chemistry. The physical and thermal properties as well as the UV protection capability of the cellulose-lignin films under different conditions are reported.



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MATERIALS AND METHODS Materials Microcrystalline cellulose (Advice HP-105) purchased from Sigma-Aldrich, was used in an airdry state. DMAc, LiCl, acetone, methanol and glycerol were of the highest commercially available purity.

A commercially available (Mead Westvaco) softwood kraft lignin (KL),

Indulin AT, was used.

Microcrystalline cellulose (MCC) Bearing Surface Azide (MCC-Az) MCC surface-tosylation was performed using tosyl chloride21. An amount of 2 g of MCC was suspended in pyridine (40 mL) and the mixture was cooled from room temperature to 10°C. Tosyl chloride (2 g) was then added, and the reaction mixture was stirred for two days at room temperature. The product (MCC-Tos) was washed with ethanol (50 mL) and deionized water (50 mL) five times each and freeze-dried. MCC-Tos was then suspended in 50 mL of DMF (N,N-dimethylformamide), followed by careful addition of 1g sodium azide. The reaction mixture was stirred at 100 °C for 24 h. After precipitation through the addition of 50 mL of deionized water and centrifugation, the product was washed five times with ethanol (50 mL) and five times with deionized water (50 mL). The resulting product was dialyzed against deionized water for 3 days and, consequently, freezes dried (MCC-Az).

Dissolution of MCC-Azin DMAc/LiCl An amount of 2g of dried MCC-N3 mixed with 25 mL DMAc was maintained at 130°Cfor 30 min. An amount of 2g of LiCl was added to the mixture and heated for 10 more minutes. Then the mixture was stirred at room temperature for 12hrs. The final transparent cellulose solution was kept in a sealed container in a refrigerator.

Kraft lignin propargylation The phenolic hydroxyl group in the lignin was replaced with a propargyl group using propargyl bromide22. A total of 1.0 g of kraft lignin was dissolved in 20 mL of aqueous 0.5 N NaOH at room temperature. An amount of 0.4 mmol of propargyl bromide per each mmol of total phenolic OH in the lignin was added to the reaction medium and heated at 75 °C for 2h under continuous stirring. The reaction medium was cooled to room temperature and the product


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precipitated by addition of 2N HCl solution to pH = 2. The product (Lignin-Pr) was washed with excess deionized water followed by drying in a freeze drier. The amount of propargylation of the product was measured by quantitative

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P NMR. About 30% of the phenolic OH in the

lignin, 1.4 mmol/g lignin, was converted to the propargyl group. Click Reaction of MCC-Az with Lignin-Pr Conditions for the Cu(I)-catalyzed Huisgen-Meldal-Sharpless 1,3-dipolar cycloaddition reaction were selected from the literature21. Lignin-Pr (0.5, 1 and 2% of MCC-N3) was dissolved in 1 mL of DMAc. An amount of 5 mg CuBr2, 10 mg ascorbic acid, and 50µL of triethylamine was then added to the lignin solution. This solution was added to the MCC-N3solution in DMAc/LiCl containing 1g cellulose and preheated to 50 °C followed by stirring at 50 °C for 12 hrs. Cellulose-lignin film preparation The final solution of the cellulose-lignin product was cast on smooth and flat glass plates. The concentration and thickness of the solution on the plate was 5%w/v and 2mm respectively. Casted cellulose-lignin solutions were immersed in an acetone bath for 1 h followed by washing with a stream of cold water for 5 hours to remove the salt completely. The final wet regenerated cellulose-lignin film was dried at room temperature on the same glass plate. FTIR FTIR spectra of the cellulose samples were measured on a Perkin Elmer Frontier FTIR spectrometer. A total of 32 cumulative scans in transmission mode were taken, with a resolution of 1cm-1 in the frequency range of 4000-600 cm-1. Irradiation of the samples Selected samples were irradiated with a 200 W Xe–Hg lamp for two hours. A small fan was used to avoid heating of the sample during irradiation. The distance of the center of the sample to the UV lamp was 25 cm. UV-Vis The optical properties of the cellulose and cellulose-lignin films were investigated using a Varian Cary 300 UV-Visible spectrometer in the wavelength range of 200-600 nm. A wavelength of 550 nm was used for determination of film transparency12.The % transparency of the film in the range of 280-320 nm (UV-B) and 320-380nm (UV-A) were determined.



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Oxidation Induction Temperature (OITtemp) The oxidation induction temperature, OITtemp (also called oxidation onset temperature OOT), is the extrapolated onset temperature during heating in the presence of oxygen that appears as an exothermic DSC signal, corresponding to the temperatures at which the material starts to effectively burn. A TA-Instrument model TA-Q100was used in the temperature range of 40−350 °C. All samples were dried at 40 °C for 24 h in a vacuum oven prior to analysis. Approximately 5 mg of a sample were weighed directly into a DSC hermetic aluminum pan, which was then covered with its lid and sealed by pressing. Three small holes were created in the lid. After being loaded into the TA-Q100,all samples were heated to 105 °C at a rate of 5 °C/min under aN2 gas stream and then isothermally conditioned at this temperature for 20 min prior to being quenched to 40 °C and held for another 5 min. Finally, the DSC thermograms were recorded by increasing the temperature to 300°C at a rate of 5 °C/min under an oxygen stream to obtain the OITtemp data. XRD The crystallinity of the original cellulose (MCC), wet cellulose film and dried cellulose film was determined using a Rigaku Smartlab X-ray diffractometer. The diffractometer was equipped with Be-filtered Cu-Kα radiation with a wavelength of 1.54 Å generated at 35 kV and 25 mA. The samples were scanned from a 2θ range from 5 to 45° at an increment of 0.05°. Relative crystallinity was calculated from the intensity measurements using the Segal method23 ( Equation 1) X % = (

) 100%

Equation 1

In this method, I representsthemaximum intensity of (002) lattice diffraction peak at diffraction angle around 2θ = 22.5° and IAM represents the intensity scattered by the amorphous component in the sample, which was evaluated as the lowest intensity at 2θ of 18°. Tensile properties Tensile tests were carried out on an Instron 4465 machine at room temperature using deformation rates of 2.5 mm/min with sample sizes of 25 x 5 x 0.050 mm. Prepared samples were strained until their ultimate break to study the strain hardening behavior. Stress versus strain was measured within the guidelines of the ASTM 638 standard and the strain hardening stiffness calculated. Independent replicates and repeats were carried out.


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RESULTS AND DISCUSSION Indulin kraft lignin was used in this study. The average weight and number molecular weight of the lignin were 6000 g/mol and 1500 g/mol respectively. Total phenolic hydroxyl group was measured by 31P NMR to be 4.6 mmol/g lignin. Incorporation of the alkyne group in lignin was achieved in a one pot reaction using propargyl bromide in NaOH solution at 80 ºC for 2 hrs(Scheme 1)22. The level of propargylation was controlled by controlling the mole ratio of propargyl bromide to total phenolic OH in the lignin. 31P NMR was used to measure the amount of lignin propargylation. A 30% conversion of total phenolic OH into alkyne group, equal to 1.4 mmol/g lignin, was used for the click reaction with the CMC-Az. Modification of the primary hydroxyl groups on the cellulose surface with the azide groups was achieved in two steps (Scheme 1)21,24. First, MCC was suspended in pyridine and treated with tosyl chloride, yielding the surface-tosylated cellulose analog. The tosyl substituents were subsequently displaced by azide groups using sodium azide in a DMF suspension, yielding MCC-Az. Reaction of the Lignin-Pr with the MCC-Az was achieved by the Cu(I)-catalyzed HuisgenMeldal-Sharpless 1,3-dipolar cycloaddition reaction. CuBr2 in combination with ascorbate in DMAc at 50 °C in the presence of triethylamine catalyst was utilized for the click reaction21,24.

Scheme 1

Clear evidence for the successful reaction of lignin-Pr with the MCC-Az was obtained from IR spectroscopic analysis (Figure 1). The IR spectrum of the azide surface modified cellulose, MCC-Az, exhibited an azide band at 2100 cm-1, within the range of 2160-2080 cm-1 expected for the antisymmetric azide stretching motion24,25.Upon reaction with the ethyne containing lignin, the azide band intensity was decreased by 75%. Due to solubility problems of cellulose and its modified products in the NMR solvents, FTIR is utilized as the main method to verify the click reaction chemistry24,25. Also for more verification, we did a control reaction; dissolved MCC-az in DMAc/LiCl was mixed with dissolved Lignin-Pr in DMAc for 24 hrs without the click reaction catalyst (CuBr2). The FTIR spectrum of the product showed no reduction at 2100 cm-



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which demonstrated that the lignin was simply mixed with the cellulose and was not covalently

bonded.

Figure 1

Images of the films after casting, washing and drying are shown in Figure 2. The bonded sample is a homogenous film with even distribution of lignin. For the control sample, an unmodified cellulose solution was mixed simply with an unmodified lignin solution without catalyst present. After regeneration with acetone, the lignin was not distributed evenly in the final film and phase separated from the cellulose (Figure 2D). The results show that lignin is not compatible with the cellulose and needs to be chemically bonded to the cellulose for uniform distribution in the film. The cellulose film and its composite with lignin were stable and transparent even after 24h soaking in water.

Figure 2

X-ray diffraction The crystal structure of the original cellulose and its prepared cellulose film with and without lignin was investigated using XRD analysis. Natural cellulosic fibers are known to display X-ray diffraction (XRD) patterns typical of cellulose type I, with the main diffraction signals at 2Ɵ values of 15°, 16°, 22.5° and 34° attributed to the diffraction planes 101, 10ī, 002 and 040, respectively26-28. Figure 3 shows the XRD patterns obtained for the MCC-Az, MCC-Az film and cellulose-lignin (2% lignin) film. Crystallinity of the original cellulose sample, MCC was calculated as about 85%29 and showed clear and sharp signals at 15°, 16°, 22.5° and 34° which is typical for pure cellulosic fiber. However, dried cellulose film after regeneration of cellulose solution in DMAc/LiCl using acetone showed a broad spectrum with three diffraction peaks at 13.4°, 14.5° and 21°which shifted to lower degrees. Due to the lack of good signals and the disruption of the crystal structure during regeneration, it is not possible to measure cellulose film crystallinity. The XRD spectra of the cellulose film containing 2% bonded lignin showed an amorphous structure as well with only three weak peaks. Calculation of the crystallinity was not possible. It


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seems that the branched structure of the lignin contributed to the lack of rearrangement and assembly of the cellulose chains into ordered structures.

Figure 3

UV Protection Due to its phenolic structure, lignin is an excellent light absorber (190–400 nm, with absorption peaks near 200, 230 and 280 nm). Absorbance of light in the range of UV-B (280-320nm) provides potential for lignin to be used as a natural UV protective material. To investigate the UV protection of cellulose transparent films containing low concentrations of lignin, cellulose films were prepared with 0.5 to 2% bonded lignin. The UV-Vis transmittance of the cellulose and cellulose-lignin films (thickness of around 50 µm) were measured in the wavelength range of 200-600nm, Figure 4. The transmittance incorporates all light transmitted in the forward direction, excluding any absorption or back scattering. The neat cellulose film alone showed a high transparency, about 95%. Films prepared through bonding of lignin with cellulose showed lower transparency. In the case of 2% lignin addition, the film had an about 60% transparency (at 550 nm). Transmittance of UV at UV-B (280–320 nm) was used to calculate the Sun Protection Factor (SPF)30.The Sun Protection Factor is widely used for sun screen creams and UV protection materials and calculated based on UV absorption of the material in the UV-B spectrum (280-320 nm) range. The percentage of UV protection is equal to 100-(100/SPF). For example, a material with SPF=15 means it can protect 100-(100/15) = 93.33% of UV-B light.

The cellulose film without lignin showed a high

transparency of 95% at 550 nm to 80% at 250 nm, indicating that the cellulose film has basically no effective UV protection in both the UV-B and UV-A ranges.

Figure 4

With bonding of only 0.5% lignin to cellulose, the transmittance of UV-B light was reduced to around 15-30% which is equal to a SPF value of 15. In the range of UV-A, the 0.5% lignin film had a UV light transmittance of 30-65%. With 2% lignin content, the film absorbed or blocked around 100% of UV-B(equal to an SPF of about 100)and also blocked a majority of UV-A (320-



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340 nm). The UV protection efficiency of the produced film is comparable to synthetic polymers coated with UV protection material31,32 The service lifetime of UV protection materials is of significant concern. To investigate effects of UV irradiation on the film UV protection stability, cellulose film as a control sample and its 2% lignin treated sample were irradiated under strong UV irradiation using a UV xenon lamp for 2 hrs and then analyzed for the UV-Vis light transmittance, Figure 5. Non-treated cellulose film UV absorption was stable after UV irradiation. Significantly, lignin containing film showed complete stability in the range of UV-B (280-320 nm). In the range of UV-A (320-400 nm), after UV irradiation the film showed only between 2-10% reduction in UV light transmittance and absorbed around 90% (average) of UV-A light.

Figure 5

Thermal cycling and elevated temperatures are also important stressors to UV protective films. The effect of being held at 120 °C for two hours on the UV-Vis light transmittance of the films is shown in Figure 6. The results revealed that the effect of heating even at 120 °C for two hours is negligible on the film UV light transmittance. Unexpectedly, the heat treatment actually improved/increased the light transmittance in the visible range.

Figure 6

Thermal Stability The thermal degradation of cellulose film and its lignin bonded sample can be evaluated by determining the oxidation induction temperature (OITtemp), which reflects the onset temperature of combustion in oxygen. The OITtemp of the cellulose film was determined to be around 245 °C (Figure 7). By bonding 2% of kraft lignin with cellulose, the OITtemp values of cellulose-lignin film increased to 262 °C. It was demonstrated that the presence of the phenolic OH groups within the lignin structure2,18,20 and the aromatic char originating from the lignin at elevated temperature33 are responsible for the beneficial effects toward oxidative, thermal, and light stability characteristics of the lignin when present in blends with other polymers.


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Figure 7

Tensile properties Mechanical properties of the films are important for different applications34.The stress–strain curves for the dried cellulose film and its 2% lignin containing sample (around 6% water content in both samples) are shown in Figure 8.

Figure 8

The cellulose film has a tensile strength of 118 MPa at break, with yield strength of 81 MPa and a Young's modulus of 3200 MPa. The maximum strain for the cellulose film was 10%. Cellulose film bonded with 2% lignin showed 92 MPa tensile strength that break with yield strength of 85 MPa and amaximum strain of around 6%. Lignin acts as a cross-linker between cellulose chains in the cellulose-lignin films and it can be the source of the lowerstrain to break. XRD results showed better crystallinity for the cellulose film than its treated sample with lignin which can be another reason for the approximately 20% higher tensile strength of the cellulose film. In comparison with other data in the literature 35-37 both the cellulose film and cellulose-lignin films herein possess reasonably high strength properties.

CONCLUSION Lignin can be used as a renewable biomass derived broad-spectrum sun blocker in cellulose transparent films. Non-derivatized cellulose film with high transparency, flexibility and mechanical properties containing small amounts of lignin could be prepared using DMAc/LiCl as the solvent but the films were not homogeneous. In contrast, after dissolution of cellulose bearing azide groups in DMAc/LiCl, up to 2% of kraft lignin bearing propargyl groups were able to be reacted with cellulose through “click chemistry” to form homogenous films. Transparency of the neat cellulose film was around 95% at 550nm without any significant UV absorption for UV-B and UV-A. The addition of up to 2%bondedlignin in the cellulose increased its UV absorption potential. Cellulose film containing 2% lignin showed around 100% absorption of UV-B (280-320 nm) and more than 90% of UV-A (320-400 nm). The prepared film was stable against elevated temperature at 120°C and UV irradiation. Tensile strengths of the cellulose and



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the cellulose-lignin films were around 90MPa with about 6% strain to break. This research demonstrated the potential of lignin as a component in cellulose-lignin UV light blocker films.

ACKNNOWLEDGMENT We would like to thank the Southeastern Sun Grant Center and USDA for the support of this project.

We would also like to thank the North Carolina State University Research and

Innovation Seed Funding program for its support.

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13 (13) Han, K.; Yu, M.: Study of the preparation and properties of UV-blocking fabrics of a PET/TiO2 nanocomposite prepared by in situ polycondensation. Journal of Applied Polymer Science, 2006, 100, 1588-1593. (14) Wang, R. H.; Xin, J. H.; Tao, X. M.: UV-Blocking Property of Dumbbell-Shaped ZnO Crystallites on Cotton Fabrics. Inorg. Chem, 2005, 44. (15) Mao, Z.; Shi, Q.; Zhang, L.; Cao, H.: The formation and UV-blocking property of needleshaped ZnO nanorod on cotton fabric. Thin Solid Films, 2009, 517,. (16) Jiang, Y.; Song, Y.; Miao, M.; Cao, S.; Feng, X.; Fang, J.; Shi, L.: Transparent nanocellulose hybrid films functionalized with ZnO nanostructures for UV-blocking. J. Mater. Chem. C, 2015, 3, 6717-6724. (17) Argyropoulos, D. S.; Menachem., S. B.; Kaplan, D. L.: Lignin.” In Biopolymers From Renewable Resources, Chapter 12,In Springer Verlag, 1998; pp 292-322. (18) Lignin: Historical, Biological and Material Perspectives; Glasser, W. G.; Robert, R. A.; Schultz, T. P., Eds., 1999 (19) Zimniewska, M.; Batog, J.; Romanowska, E. B. B.: Functionalization of Natural Fibres Textiles by Improvement of Nanoparticles Fixation on Their Surface. Journal of Fiber Bioengineering and Informatics, 2012, 5, 321-339. (20) Sanchez, C. G.; Alvarez, L. A. E.: Micromechanics of lignin/polypropylene composites suitable for industrial applications. Angew. Makromol. Chem., 1999, 272, 65-70. (21) Sadeghifar, H.; Filpponen, I.; Clarke, S. P.; Brougham, D. F.; Argyropoulos, D. S.: Production of cellulose nanocrystals using hydrobromic acid and click reactions on their surface. J Mater Sci, 2011, 46, 7344-7355. (22) Sen, S.; Sadeghifar, H; Argyropoulos, D S.: Kraft Lignin Chain Extension Chemistry via Propargylation, Oxidative Coupling, and Claisen Rearrangement. Biomacromolecules, 2013, 14, 33993408. (23) Segal, J. J.; Creely, A. E.; Martin, J.; Conrad, C. M.: An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose using X-ray Diffractometer. Tex. Res. J, 1959, 29, 786-794. (24) Feese, E.; Sadeghifar, H.; Gracz, H. S.; Argyropoulos, D. S.; Ghiladi, R. A.: Photobactericidal Porphyrin-Cellulose Nanocrystals: Synthesis, Characterization, and Antimicrobial Properties. Biomacromolecules, 2011, 12, 3528-3539. (25) Lambert, J. B.; Shurvell, H. F.; Lightner, D. A.; Cooks, R. G.: Organic Structural Spectroscopy; Prentice-Hall, Inc.: Upper Saddle River, NJ,., 2001. (26) Ioelovich, M. Y.; Veveris, G. P.: Determination of Cellulose Crystallinity by X-ray Diffraction Method. J. Wood Chemistry, 1987, 5,, 72-80 (27) Jua, X.; Bowdenb, M.; Browna, E. E.; Zhanga, X.: An improved X-ray diffraction method for cellulose crystallinity measurement. Carbohydrate Polymers, 2015, 123 476-481. (28) Thygesen, A.; Oddershede, J.; Lilholt, H.: On the determination of crystallinity and cellulose content in plant fibres. Cellulose, 2005, 12, 563-576. (29) Segal, J. J.; Creely, A. E.; Martin, J.; Conrad, C. M.: An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose using X-ray Diffractometer. Tex. Res. J., 1959, 29, 786-794. (30) Dutra, E. A.; Oliveira, D. A. G. d. C.; KedorHackmann, E. R. M.; Santoro, M. I. R. M.: Determination of sun protection factor (SPF) of sunscreens by ultraviolet spectrophotometry. Brazilian Journal of Pharmaceutical Sciences, 2004, 40, 381-385. (31) Olkhov, A. A.; Zaikov, G. E.: UV-Stability LDPE - Films. Polymers Research Journal 2014, 4, 211-221. (32) Parejo, P. G.; Zayata, M.; Levy, D.: Highly efficient UV-absorbing thin-film coatings for protection of organic materials against photodegradation. J. Mater. Chem., 2006, 16, 2165-2169



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15

Figures captions

Figure 1. FTIR spectra of microcrystalline cellulose bearing azide group (MCC-Az) and its treated sample simply with 2% lignin containing ethyne groups after simple mixing and after bonding with the “Click Reaction”

Figure 2. Cellulose film (2A), Cellulose azide film with 1% bonded lignin (2B), Cellulose azide film with2% bonded lignin (2C) and 2% lignin simply physically mixed with cellulose (2D). All films were prepared by making solutions in DMAc/LiCl and then using acetone as coagulator

Figure 3. XRD spectra of the MCC-Az, MCC-Az film and cellulose-2%lignin film

Figure 4. Transmittance of cellulose and cellulose bonded with lignin films from 200-600 nm at different levels of lignin loading

Figure 5. Effects of high power UV irradiation of cellulose film and the cellulose bonded with 2% lignin film sample on their light transmittance behavior.

Figure 6. Effects of heating to a temperature at 120 °C for two hours of the cellulose film and cellulose bonded with 2% lignin film sample on their light transmittance behavior

Figure 7.Heat flow versus temperature in an oxygen environment for cellulose film and cellulose bonded with 2% lignin film sample to determine the oxidation induction temperature (OITtemp) Figure 8. Tensile strength of cellulose film and cellulose bonded with 2% lignin film

Scheme Captions Scheme 1 General route for the synthesis of cellulose-lignin conjugate



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16

Scheme 1


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17

Figure 1

100

98

80

95 92

60

89

MCC-Az bonded with Lignin MCC-Az mixed with lignin MCC-Az

86

2100 2160

2090

40 83 2020

20

0 3650

3150

2650

2150

1650 -1

Wavenumber ( CM )


1150

650

Transmittance, %

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



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

18

Figure 2


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Figure 3

14000 12000 MCC-Az

Intensity ( au)

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


10000

MCC-Az film MCC-Az + 2% Bonded Lignin Film

8000 6000 4000 2000 0

5

10

15

20

25

30

2ɵ, Degree


35

40


20

Figure 4

100

Cellulose Film (CF)

90

CF+0.5% Lignin

80

% Transmittance

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

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CF+1% Lignin

70 60 50

CF+2% Lignin

40 UV-B

30 20

UV-A

10 0 210

260

310

360

410

460

Wavelength, nm


510

560

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21

Figure 5 100

Cellulose film (CF)

90

CF, 2 hrs UV irradiated

80 70

% Transmission

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


CF+2% bonded lignin 2 hrs UV irradiated

60 50

CF+2% bonded lignin 40 30 20 10 0

210

260

310

360

410

460

Wavelength, nm


510

560


22

Figure 6 100

Cellulose film (CF)

90

CF, 2 hrs heated at 120 °C

80

Transmission, %

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

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CF +2% bonded lignin , 2 hrs heated at 120 °C

70 60 50

CF +2% bonded lignin

40 30 20 10 0 200

250

300

350

400

450

wavelength, nm


500

550

600

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Figure 7

15

Cellulose film

12.5

Heat Flow, m/w

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


10 7.5 262 °C 5 245 °C 2.5

Cellulose film + 2% lignin

0 100

150

200

250

Temperature, °C


300


24

Figure 8

120 Cellulose film 100

Stress, Mpa

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

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80

Cellulose film + 2% bonded lignin film

60

40

20

0 0

0.02

0.04

0.06

0.08

Strain, mm/mm


0.1

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For table of contents use only

Cellulose-Lignin Biodegradable and Flexible UV Protection Film Hasan Sadeghifar, Richard Venditti, Jesse Jur, Russell E. Gorga, Joel J. Pawlak

A transparent cellulosic film with less than 2% chemically bonded lignin can absorb and protect from UV light.


Cellulose-Lignin Biodegradable and Flexible UV Protection Film

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