Research Article pubs.acs.org/journal/ascecg
Sustainable Composites from Biodegradable Polyester Modified with Camelina Meal: Synergistic Effects of Multicomponents on Ductility Enhancement Zhaoshu Chen,† Ning Lin,† Shanjun Gao,† Changhua Liu,‡ Jin Huang,*,†,‡ and Peter R. Chang*,§ †
School of Chemistry, Chemical Engineering and Life Sciences, College of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, P. R. China ‡ School of Chemistry and Chemical Engineering, Southwest University, No. 2 Tiansheng Road, BeiBei District, Chongqing 400715, China § Bioproducts and Bioprocesses National Science Program, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, Saskatchewan S7N 0X2, Canada S Supporting Information *
ABSTRACT: Biodegradable composites were prepared via a melt compression molding process with dehulled camelina meal (DeCM) as the biomass-based filler and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3,4)HB) or poly(butylene succinate) (PBS) as the aliphatic polyester matrix. The incorporation of 25 parts DeCM into the composite promoted an impressive increase of 461% in the elongation at break of the P(3,4)HB-based composites. Concurrently, the elongation at break of PBS-based composites containing 20 parts of DeCM increased by 71% over the neat materials. Extraction of components from the DeCM (oil and protein) showed that oil had a critical plasticization effect that enhanced the ductility of the composites. Compared with neat materials, the presence of DeCM filler had no significant effect on the thermal properties of the composites and preserved the original crystalline structure of the polyester component in the composites. Renewable, economical, and biodegradable DeCM is a promising functional biomass-based filler for polyester-based composites, and it is worth noting that the synergistic effects of multicomponents in DeCM played a key role in ductility enhancement. KEYWORDS: Sustainable composites, Mechanical properties, Renewable resources, Camelina
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INTRODUCTION Global development and demand for biodegradable materials have experienced growth over the past several decades thanks to public concern about the environment, climate change, and the depletion of fossil fuels. Polyester is a category of polymers that contain an ester functional group in their chemical structure; aliphatic polyesters, including polylactic acid (PLA), polycaprolactone (PCL), polyhydroxybutyrate (PHB), and poly(butylene succinate) (PBS), generally exhibit superior biodegradability, biocompatibility, and processability.1−3 PHB is a polyhydroxyalkanoate (PHA) that is generally recognized as a bioderived and biodegradable plastic.4,5 Introduction of the comonomer unit, 4-hydroxybutyrate, results in the fabrication of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) which has a lower melting temperature and lower degree of crystallinity, and has been explored for use in the food packaging industry,6 in agricultural applications,7 and in biomedical tissue engineering.8 PBS, another important aliphatic polyester synthesized by polycondensation of 1,4-butanediol with succinic acid, is considered to be a promising material in many fields because it has excellent biodegradability, melt processability, and chemical resistance.9,10 Despite numerous advantages, the © XXXX American Chemical Society
practical application of P(3,4)HB and PBS as plastic products is restricted by their high cost and compromised mechanical properties (such as brittleness and low toughness).11,12 Physical blending of polyester with another type of material is regarded as a promising strategy for enhancing performance and resulting in composites of lower cost and/or ease of manufacturing. The incorporation of diverse inorganic and organic fillers, such as lignin,13 calcium carbonate,14 graphene,15,16 fiber,17 and cellulose,18 in P(3,4)HB and PBS polymer matrices to enhance the composites’ mechanical and thermal properties has been reported. Indeed, incorporation of rigid nanofillers, such as inorganic nanosilica19 or organic cellulose nanocrystals20 at low loading levels (1−5 wt %), provides mechanical reinforcement to enhance the modulus of the polyester composites. However, the presence of these rigid nanoparticles commonly reduced the elongation at the break of the composites, and the tendency of the nanoparticles to selfaggregate at higher concentrations (>10 wt %) had an adverse Received: February 3, 2016 Revised: April 11, 2016
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DOI: 10.1021/acssuschemeng.6b00255 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
Figure 1. Component separation of DeCM and composite preparation with P(3,4)HB and PBS matrices. pressure released. The two composite series were coded according to the polyester matrix and filler as P(3,4)HB/DeCM-x and PBS/DeCMx, where x was the theoretical DeCM concentration (parts) in the composite. Neat P(3,4)HB and PBS samples were also prepared using the same melt compression approach. Extraction of DeCM Components and Composite Preparation. In order to investigate the effects of key components of the meal on the mechanical properties of the composites, oil and protein were extracted from the DeCM, and the extracted meals were separately blended with the polyester matrices. Oil was extracted from DeCM using Soxhlet extraction with anhydrous ethanol for 24 h (the anhydrous ethanol was replaced every 12 h), as depicted in Figure 1. Defatted DeCM was dried at 60 °C for 24 h and then mixed with polyester using the melt compression treatment as described above to prepare composites, labeled as polyester/DeCM(O-x). Defatted DeCM was also further treated with 0.1 wt % NaOH, at a solution to meal ratio of 20:1 for 1 h at 40 °C, to solubilize and remove protein. The treated meal was centrifuged at 8000 rcf for 10 min to remove the alkali solution and then washed with 10× distilled water and recentrifuged. Washing of the meal was repeated twice. A similar procedure used for the separation of components was reported by Reddy et al.21 The oil and protein depleted product was freeze-dried and used to prepare composites as above (coded as polyester/ DeCM(O/P)-x). Characterization. Compositional analysis of the DeCM powders was performed using AOAC official methods (Association of Official Analytical Chemists, 2006) for protein, oil, ash, and moisture analysis. The mechanical properties of the composites, including tensile strength (σb), elongation at break (εb), and Young’s modulus (E), were measured on a CMT6503 universal testing machine (SANSA, Shenzhen, China) with a tensile rate of 10 mm/min according to the GB/T 1040-2006 method. Composite samples were cut in a dumbbell shape with a length and width of 60 mm × 2 mm. A mean value of five replicates for each sample was recorded. The rheological properties of the melted composites were investigated using a DHR rotational rheometer (TA Instruments, Germany) with two parallel plates (ϕ = 25 mm). The composite sample was loaded onto the bottom plate and allowed to premelt for 5 min at 160 °C for P(3,4)HB and 120 °C for PBS. A dynamic frequency sweep over a frequency range 1−500 rad/s was performed to determine the dynamic properties of the composites. The strain was controlled at 1% and 10% for the P(3,4)HB series and PBS series composites, respectively.
effect on the mechanical properties of the composites. We postulate that the performance of polyester-based composites could be enhanced by exploring the use of some underutilized functional biofillers. Camelina meal (containing a significant amount of mucilage from the seed coat) is a readily available, low cost, and biodegradable21 bioproduct derived from the renewable and sustainable crop, Camelina sativa. In this study, dehulled camelina meal (DeCM) (free of seed coat) was used for the first time as a biomass filler in P(3,4)HB and PBS composites to explore whether DeCM can be used as a functional and economical filler in the composites. Concurrently, the effect of the components and their possible interaction with the polymer matrix will be investigated by melt rheology and scanning electron microscope observation.
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EXPERIMENTAL SECTION
Materials. Commercial poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3,4)HB) containing 5% 4HB with an average molecular weight (Mw) and molar-mass dispersity of 3.94 × 105 Da and 1.21, respectively, was purchased from Tianjin Green Bioscience Corporation (Tianjin, China). Commercial poly(butylene succinate) (PBS) with an Mw and molar-mass dispersity of 1.29 × 105 Da and 1.26, respectively, was purchased from Anqing Hexing Chemical Co., Ltd. (Anhui, China). Camelina (Camelina sativa) seeds were procured from Terramax Corporation (Qu’Appelle, Saskatchewan, Canada). Dehulled camelina meal (DeCM, representing about 80% of original seed weight) was obtained from a minipilot plant located at the Saskatoon Research and Development Centre through a combination of milling, sieving, and cleaning until clean meal (free of brown specks from seed coats) was achieved. Composite Preparation. An internal mixer (SU-70, Changzhou Suyan Science and Technology Co., Jiangsu, China), preheated to 140 °C for use with P(3,4)HB or to 120 °C for PBS, was used to prepare homogeneous blends of polyester/DeCM by mixing at 48 rpm for 10 min. The polyester content (P(3,4)HB or PBS) was controlled at 100 parts, and the DeCM content was varied to be 5, 10, 15, 20, 25, and 30 parts in the final blend. Biodegradable composite films were formed by compression molding of the obtained blends using a hot press (R3202, Wuhan Qien Science & Technology Development Co., Wuhan, China) for 10 min at 10 MPa and 160 °C for P(3,4)HB or 120 °C for PBS. The system was then water-cooled to room temperature and the B
DOI: 10.1021/acssuschemeng.6b00255 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
Figure 2. Effect of DeCM content on the mechanical properties of P(3,4)HB/DeCM composites (A) and PBS/DeCM composites (B).
Table 1. Reduction of Costs for Polyester/DeCM Composites ingredients price (¥/t)d reduction of cost (%)
composites
DeCMa
P(3,4)HBb
PBSc
P(3,4)HB/DeCM-25
P(3,4)HB/DeCM-30
PBS/DeCM-20
PBS/DeCM-25
2000
50 000
30 000
40 400 19.20
38 923 22.15
25 333 15.56
24 400 18.67
a
Alibaba Group in China. Cited from http://detail.1688.com/offer/520157632359.html?spm=0.0.0.0.gHsanx. Retrieved Jan 25, 2016. bChanpratee, S. Current trends in biodegradable polyhydroxyalkanoates. Biosci. Bioeng. 2010, 110, 621−632. Retrieved Jan 25, 2016. cAnqing He Xing Chemical Corporation Limited in China. Cited from http://www.aqhex.cn/. Retrieved Jan 25, 2016. dCan convert to US$ by multiply 0.15 (approx) from Chinese Yuan. Scanning electron microscope (SEM) observation of the DeCM powders and the composites was performed on a JSM-5610LV scanning electron microscope (JEOL Ltd., Japan). The composite sample was quenched in liquid nitrogen and fractured, and the fracture surfaces were gold-coated for observation. Differential scanning calorimetry (DSC) was performed on a NETZSCH DSC 214 instrument (NETZSCH Co, Selb/Bavaria, Germany) under nitrogen at a heating or cooling rate of 20 °C/min. The composite sample was scanned over a temperature range −70− 200 °C after pretreatment to eliminate thermal history (i.e., heating from room temperature to 110 °C and then cooling to −70 °C). X-ray diffraction (XRD) measurements were performed on D8 Advance X-ray diffractometer (Bruker, Germany) with Cu Kα radiation (λ = 0.154 nm) over the range 2θ = 3−35° using a fixed time mode with a step interval of 0.02°.
content was >10 parts. However, elongation at break (εb) increased with the introduction of the DeCM filler. As shown in Figure 2, the εb value of the P(3,4)HB/DeCM-25 composite increased by 461% in comparison with that of neat P(3,4)HB, and the εb value of the PBS/DeCM-20 composite increased by 71% compared to that of neat PBS. With the incorporation of the biomass filler (DeCM), the elongation at break of polyester-based composites increased significantly while the strength and modulus of the composites remained at a sustained level. The main limitation to wider application of biodegradable polyesters in composites is their relatively high price. Partial replacement of the polyester component with low cost biomass filler (DeCM) resulted in composites that exhibited improved elongation at break and preserved biodegradability, as well as a cost savings. The estimated prices of composites developed from two kinds of polyester and DeCM are shown in Table 1. While preserving their mechanical properties, the introduction of DeCM in the composites will reduce costs by 19−22% and 16−20% for P(3,4)HB and PBS, respectively. In order to investigate the effects of different components of DeCM on elongation at break, the components were removed and the extracted meals used in composite preparation. Polyester/DeCM(O) composites were prepared using defatted DeCM as filler, and polyester/DeCM(O/P) composites were developed from DeCM with oil and protein removed. Comparisons of the mechanical properties of the P(3,4)HB/ DeCM-25, P(3,4)HB/DeCM(O)-25 and P(3,4)HB/DeCM(O/P)-25 composites, as well as the PBS/DeCM-20, PBS/ DeCM(O)-20, and PBS/DeCM(O/P)-20 composites, are
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RESULTS AND DISCUSSION Component Analysis and Separation of the DeCM Biomass. Compositional analysis of dehulled camelina meal (DeCM) included determination of protein (45.32%), oil (23.40%), carbohydrates (25.11%), and ash (6.13%) on a dry weight basis. SEM observation revealed the spherical morphology of DeCM particles shown in Figure 1. Mechanical Properties of Polyester/DeCM Composites. The mechanical properties of P(3,4)HB/DeCM and PBS/DeCM composites with varying DeCM contents are shown in Figure 2 and Table S1 (Supporting Information). Generally, as compared to the neat P(3,4)HB or PBS materials, the Young’s modulus (E) and tensile strength (σb) of the composites increased slightly with the addition of low levels of DeCM (
