Biocomposites Developed Using Biopolyesters as Matrix

Abstract

The biopolyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) was used as matrix, and flax fibers were used as reinforcement to develop composites. Since P(3HB-co-3HHx) copolymer is hydrophobic and flax fibers are hydrophilic, the fibers were either acetylated or grafted with polyester to improve adhesion between the fibers and the matrix. In addition, longer length flax fibers were used in matrix form, and short flax fibers were mechanically mixed into the matrix and compression molded into composites. Figure 70.1 shows the strength and modulus of the composites obtained using various configurations of the fibers. As seen from the figure, the addition of the fibers, especially the long fibers, substantially increased the strength and modulus of the composites. However, the strength of the short fiber-reinforced composites (black bars) does not show a major change with the modification of the fibers, but the modulus of the composites obtained using acetylated fibers (A) was considerably higher than the composites without modification (U) and those grafted with polyester (P) [07Zin]. In addition to flax fibers, several other fibers such as abaca and jute have been used as reinforcement with PHBV as the matrix. Some of the properties of the composites developed using PHBV as matrix and natural fibers as reinforcement are provided in Table 70.1. PHBV matrix was also reinforced with 30 or 40 % bamboo fiber having a length of 5 cm and diameter between 10 and 100 μm [08Sin]. No significant increase in properties was observed when the fiber content was increased from 30 to 40 %, but the tensile modulus had increased by 175 % after incorporating the fibers compared to the neat polymer. The improvement in tensile modulus was close to the theoretical possible increase that was calculated using Christensen’s equations. A number of voids and clusters of fibers were observed in the fractured surfaces that were responsible for the relatively low impact and tensile strength [08Sin]. SEM images in Fig. 70.2 show that at 40 % fiber loading, there are excessive fiber and considerable low levels of matrix that lead to poor binding and therefore relatively poor properties. Table 70.2 lists some of the properties of the bamboo–PHBV composites at the two different loading levels studied.