DEVELOPMENT OF FLAXSEED OIL-BASED BIO-RESIN FOR FLAX FIBER REINFORCED BIOCOMPOSITES
Date
2015-09-01
Authors
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Journal ISSN
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ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
Researchers have extensively studied the use of triglyceride oils to develop biopolymers for various applications, such as coatings, paints, inks, plasticizers, and lubricants. Because of its wide availability and high unsaturated fatty acid content, soybean oil has usually been the focus of studies to develop biopolymers for the composite industry. However, like soybean oil, flaxseed oil is also comprised of mostly unsaturated fatty acids (more than 90% w/w), and although it has not been studied as much as soybean oil, it can also be used to develop bio-resin for composite applications. As a leading producer and exporter of flaxseed, Canada has abundant flaxseed oil and flax fiber available to produce renewable value-added products.
In this research, Saskatchewan-grown flaxseed oil was used to develop a bio-resin, which was investigated for its application in developing flax fiber-reinforced biocomposites. Flaxseed oil contains high levels of unsaturated fatty acid (linolenic acid = 54% w/w as shown by 1H NMR and 13C NMR spectra) and has double bonds that can be used for polymerization (shown by FTIR spectra). In this research, flaxseed oil-based bio-resin was synthesized via epoxidation and acrylation reactions. There were 3.7 epoxy groups per triglyceride molecule present in the epoxidized flaxseed oil (EFO) and 2.6 acrylate groups per triglyceride molecule present in the acrylated epoxidized flaxseed oil (AEFO). A vacuum-assisted resin transfer molding (VARTM) process was used to produce the AEFO-based biocomposite test specimens.
The AEFO resin was compared to one of the commercially available versatile biopolymers, polylactic acid (PLA), and to two commonly used petroleum-based polymers, polypropylene (PP) and high-density polyethylene (HDPE). The density of the AEFO resin (1.166 g/cm3) was found to be higher than the densities of PP (0.906 g/cm3) and HDPE (0.946 g/cm3), but it was slightly lower than the density of PLA (1.189 g/cm3). Less than 1% w/w of water was absorbed by all four polymer-based samples tested in this study. DSC results showed that AEFO has a glass transition temperature (Tg) of 62 oC, which is similar to the Tg (56 oC ) of PLA; this indicates a high cross-link density. The mechanical properties of the developed AEFO bio-resin are as follows: tensile strength = 29.8 ± 1.5 MPa; Young’s modulus = 373 ± 19 MPa; flexural strength = 53.5 ± 2.3 MPa; flexural modulus = 2.84 ± 0.15 GPa; and Rockwell hardness number = 90 ± 4. PLA was found to be the strongest and hardest of the four polymers tested; it had the highest tensile strength, Young’s modulus, flexural strength, and flexural modulus. However, the mechanical properties of AEFO indicated that it was stronger than PP and HDPE, and its properties were closer to those of PLA. The stress-curve of the AEFO sample showed some ductility as well. The mechanical properties of the AEFO bio-resin were also comparable to the mechanical properties of the acrylated epoxidized soybean oil (AESO) resin found in the literature.
Silane-treated flax fiber-based biocomposites were developed using the AEFO bio-resin produced by the VARTM process. The effect of fiber loading was investigated by varying the amount of flax fiber as follows: 2%, 5%, and 10% w/w. To enhance the strength of the polymer matrix, styrene was added at five different levels (10%, 20%, 30%, 40%, and 50% w/w). The mass increase percentage was found to be less than 1.5% for the maximum flax fiber content used in this study (10% w/w). The addition of styrene had no effect on the water absorption characteristics of the AEFO-based biocomposites. The flax fiber served as reinforcement in the AEFO biocomposites. The mechanical properties of the AEFO-based biocomposites (i.e., tensile strength, Young’s modulus, flexural strength, and flexural modulus) improved with an increase in the flax fiber content. The mechanical properties of the AEFO-based biocomposite with maximum flax fiber content in this study (10% w/w) were as follows: tensile strength = 31.4 ± 1.6 MPa; Young’s modulus = 520 ± 26 MPa; flexural strength = 53.5 ± 2.3 MPa; flexural modulus = 2.98 ± 0.17 GPa; and Rockwell hardness number = 97 ± 5. Adding styrene to AEFO enhanced the hardness of the AEFO biocomposite material as well as its tensile strength, Young’s modulus, and flexural modulus; however, adding styrene also decreased the composites’ flexibility, thus decreasing its flexural strength.
The AEFO-based biocomposites were compared with the PLA-, PP-, and HDPE-based biocomposites. The PLA, PP, and HDPE polymer matrices were reinforced with the silane-treated flax fiber via extrusion and injection molding processes. The densities of all four types of biocomposites were proportional to the densities of their respective polymers. It was found that the AEFO, PP, and HDPE biocomposites had very low density deviation from their respective ideal densities. However, the PLA biocomposite showed a higher density deviation of 13% from its ideal density, thus indicating a large amount of porosity in its test specimen. The mass increase observed during the water absorption tests was similar for all biocomposites, and it was less than 2% w/w for each biocomposite. The tensile properties (tensile strength and Young’s modulus) and the flexural properties (flexural strength and flexural modulus) of the AEFO-, PP-, and HDPE-based composites increased with an increase in the flax fiber content. However, tensile strength and flexural strength of the PLA-based biocomposites decreased with an increase in the flax fiber content due to the poor fiber-matrix interfacial adhesion. Based on the study and the mechanical test results, AEFO proved to have the potential to replace PP- and HDPE-based biocomposite material. The PLA-based natural fiber biocomposite might need some compatibilizer to improve the interfacial adhesion between fiber-matrix.
Description
Keywords
Flaxseed oil, Biopolymer, Flax Fiber, Biocomposite, Epoxidation, Mechanical properties
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemical and Biological Engineering
Program
Biological Engineering