Biofiber-Reinforced PHB Composites

Poly(3-hydroxybutyrate] (PHB] is the main representative of PHAs and was, in fact, the first PHA discovered. PHB is a linear saturated potyester with similar properties as thermoplastics. PHB is similar in its material properties to potypropylene, with a good resistance to moisture. Like most other biopotymers, their weaknesses are low thermal stability and low toughness. High cost of PHBs is 

Hossain et al. [45] studied the effects of surface modification of jute libers and nanoclay on jute-Biopol green composites. Four subsequent chemical treatments including detergent washing, dewaxing, alkali treatment, and acetic acid treatment were performed to facilitate better bonding between the fiber and matrix. The scanning electron microscopy and Fourier transform infrared spectroscopy study confirmed improved fiber surfaces for better adhesion with matrix after final treatment. Enhanced thermal 

Biocomposites from a bamboo fiber and PHBV were fabricated using extrusion followed by injection molding by Singh et al. [47]. Tensile and flexural modulus of this biocomposite increased with fiber loading. The storage modulus also improved with fiber 

Keller [49] reported that no improvement of the tensile strength and impact strength of the brittle PHBV matrix could be achieved when reinforced with hemp fibers, whereas its tensile modulus was increased up to 6 GPa. As the composite behavior is determined by the matrix, the fiber reinforcement is accompanied by a reduction of the impact strength. 

Zini et al. [50] prepared composites of a bacterial copolyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate], P(3HB-co-3HH), reinforced with flax fibers by compression molding. In order to improve fiber-matrix adhesion in composites, fibers chemically modified at the surface (by acetylation or by short-chain-PEG grafting] were also used. The best results were obtained with surface acetylated fibers. In the flax fiber composites the crystallization rate of P(3HB-co-3HH] remarkably increased compared with that of the plain polyester. The fibers displayed a nucleating effect on P(3HB-co-3HH] crystallization, whose magnitude depended on fiber surface chemistry. This feature was confirmed by the appearance of trans-crystallinity in isothermal crystallization experiments run in a hot stage of a polarized optical microscope. 

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