Modification of polyhydroxybutyrate (PHB) biopolymer and production of PHB nanocomposites with nanocellulose

This study produced a PHB-g-MA copolymer by grafting maleic anhydride (MA) to Polyhydroxybutyrate (PHB) biopolymer. It aimed to reduce its fragility by improving the morphological structure of PHB by adding this copolymer to neat PHB. The literature shows that the morphological structure of different polymers is improved by adding MA, thus improving mechanical properties. It has been observed that the properties of many polymers (polypropylene and polyethylene etc.), such as strength, color absorption, adhesion, hydrophilicity, and antistatic properties, have improved after MA grafting. In our study, MA grafting was performed on PHB in benzoyl peroxide's (BPO) presence. The efficiency between these methods was investigated using 5% and 10% wt MA microwave (MW) and extruder (Ext) grafting methods in copolymer (PHB-g-MA) production. Among the methods used in producing PHB-g-MA graft polymers, the grafting rates of graft polymers obtained by the extruder method were higher. Aysa Instruments' twin screw extruder was used to prepare PHB-g-MA-added PHB mixtures and CNC-added nanocomposites. The mixtures and nanocomposites were produced using the BOY 22A brand injection molding machine. It was observed that the morphological structures and mechanical properties of the mixtures improved with the addition of PHB-g-MA to PHB. According to XRD results, the crystallinity of neat PHB increased with the addition of MA. No significant difference was observed in melting (Tm) and crystallization (Tc) temperature values with the addition of PHB-g-MA. It was observed that the storage and loss modulus were improved with the addition of PHB-g-MA, and the tan delta values of the mixtures were similar. In the rheological properties, it was observed that the storage and loss modulus of the PHB and PHB-g-MA added mixtures increased as the frequency values increased. The mechanical properties of the mixtures with PHB-g-5%-MA added, obtained by microwave method among PHB-g-MA copolymers, are better. For this reason, this copolymer was used to produce crystalline nanocellulose (CNC) added nanocomposite, the second step of the study. Nanocomposites were prepared using 1.5% and 3% wt PHB-g-MA and 0.125%, 0.25% and 0.5% wt CNC. This step investigated the effects of MA addition to PHB on PHB-CNC composites. The addition of PHB-g-MA and CNC positively affected the mechanical properties of PHB. With the addition of PHB-g-MA copolymer, CNC fibers are generally homogeneously dispersed in the polymer. According to the DSC results, there was almost no change in the Tm and Tc values of the samples. It was observed that the storage and loss moduli increased with the addition of PHB-g-MA+CNC. According to XRD results, the crystallinity of the composites decreased with the addition of PHB-g-MA+CNC. The storage and loss moduli of PHB and composites increased as the frequency value increased. The addition of PHB-g-MA improved the biodegradation of PHB. In the fungi test, less growth occurred in pure PHB compared to PHB-g-MA-added mixtures. In morphologic structure, it was observed that the deformation on the surface after aging was less in the PHB-g-MA-MW mixtures than in the PHB-g-MA-Ext mixtures. The surfaces of the mixtures with the addition of PHB-g-MA were flatter and smoother. It was observed that the color stability of the mixtures with PHB-g-MA addition containing high MA increased. It can be said that the biodegradation property of PHB improved with the addition of PHB-g-MA and CNC. When neat PHB and PHB-g-MA+CNC doped composites were compared, a higher fungal growth was observed in neat PHB compared to composites. It was observed that adding PHB-g-MA+CNC increased its resistance to outdoor conditions. It was observed that the cracks and deformations on the surface decreased as the ratio of PHB-g-MA and CNC increased. The color stability of the composites increases as the PHB-g-MA+ CNC ratio rises. Surface roughness values decrease with the addition of PHB-g-MA+CNC; thus, smoother composites are obtained. According to the DMA result, it can be said that the composites exposed to long-term outdoor conditions with the addition of CNC are more durable than the mixtures added with PHB-g-MA.