Study On Modification Of Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) And Properties Of Ramie/PHBV Composites

With the development of technology on biodegradable polymers and increasing awareness onenvironment protection, green composites deriving from renewable resources have received greatscientific attention due to its biodegradability and compatibility. Bacterially synthesizedpoly-(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) is produced by nutrient deprivedmicroorganisms. PHBV has good mechanical and thermal properties resembling polypropylene,showing very promising potential to provide benefit to natural environment. Among naturalcellulose fibers, ramie fiber has drawn great attention due to its valuable mechanical propertiesand abundant natural resources. Therefore, ramie fibers reinforced PHBV composite would havethe best potential for a composite of its fair mechanical performance as well as biodegradability.This study can be divided into3parts: the first part is on the modification of PHBV. Practicalapplication of PHBV has been limited by its brittleness. Modification of PHBV by melt blendingwith Poly(butylenes succinct)(PBS) and chemical copolymerization with PBS were conductedand phase behavior, crystal structure, crystallization kinetics and mechanical properties of purePHBV and modified PHBV were investigated. The second part is on the modification of ramiefibers to enhance the interfacial bonding between ramie fibers and PHBV. Plasma treatment inMethyl acrylate and butyl acrylate environments were conducted on surface of ramie fibers. Thethird part is on the properties of ramie fibers reinforced PHBV composite. Composites wereprepared by heat press method. Influence of PBS content and plasma treatment on properties ofcomposites was investigated.Modification of PHBV by blending with PBS was investigated. The results show theincompatibility between PHBV and PBS proven by Differential Scanning Calorimeter (DSC)analysis which showed two independent melting points corresponding to those of neat componentsand SEM observation on fracture surface. No new groups and no obvious crystal structure changewere found by Fourier transform infrared spectroscopy (FTIR) analysis and X-ray Diffraction (XRD) analysis. Polarized Optical Microscopy (POM) observation showed obvious decrease ofcrystal size in blends. Mechanical properties of blends were examined by tensile testing. It isfound that the tensile strength of blends were slightly decreased while their elongation rate atbreak were highly increased.Modification of PHBV by chemical copolymerization (PHBV/PBS80/20) was investigated.Both DSC analysis and SEM observation results showed increased compatibility between PHBVand PBS. Crystal size of PHBV was greatly decreased observed under POM. Tensile strength ofPHBV was slightly decreased while elongation rate at break is highly increased which is higherthan that of PHBV/PBS(80/20) melt blend.Plasma treatment in methyl acrylate and butyl acrylate enviroments was conducted. Roughersurface of ramie fiber was found after plasma treatment and its roughness increases with theincrease of treatment duration. The difference of gas has little influence on its surface roughness.X-ray photoelectron spectroscopy (XPS) analysis shows an increase of carbon content and fiberstreated with60s methyl acrylate plasma treatment got the highest carbon content. The advancingcontact angles of the plasma treated ramie fibers are raised from66.3°to86.4°. The interfacialshear strength(IFSS) between PHBV and ramie fibers are increased after plasma treatment andthat of fibers treated with60s methyl acrylate plasma treatment is enhanced up to21.1Mpa,31.1%higher than that of untreated group.After blending with PBS, tensile strength of ramie fiber reinforced PHBV composite isslightly decreased while its bending strength is not affected. Plasma treatment has a positiveinfluence on its mechanical properties with an increase of up to6.6%on its tensile strength and11.7%on its bending strength.