Modification Study On Biodegradable Polymers: Poly(_L-lactide) And Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Biodegradable polymers has attracted much attention because its biodegradable,biocompatible, producible from renewable resources, and nontoxic to the human body and the environment. Recent innovation on the production process has lowered significantly the production cost, which further stimulates the investigation on its properties and potential applications. However, the shortcomings of biodegradable polymers limit its development. The main content of this paper is modification study of poly(L-lactide)(PLLA) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P34HB)respectively.(1)Montmorillonite(MMT) generally has weak nucleating ability or even retarded crystallization for PLLA depending on the dispersion morphology in the matrix. A novel MMT with a nucleating surface(NMMT) chemically supported by calcium phenylphosphonic acid(PPCa)(an effective nucleant of PLLA) was prepared through the chemical reaction between phenylphosphonic acid(PPOA) and a calcium ion on the surface of MMT for the first time. Differential scanning calorimetry,infrared spectroscopy and wide-angle X-ray diffraction confirm the reaction between PPOA and Ca-montmorillonite and the formation of PPCa on the surface of MMT.Then, NMMT was introduced into PLLA via simple melt blending. The most intriguing result is that the crystallization rate of PLLA greatly increases after incorporation of NMMT, and the crystallization rate of PLLA increases with increasing NMMT fraction and decreasing MMT/PPOA mass ratio. The nucleation density of PLLA increases and the spherulite size decreases significantly in the presence of NMMT. Moreover, the tensile test results show that NMMT has a strengthening effect on the amorphous PLLA. Through a short time annealing procedure, the mechanical properties such as the tensile modulus and storage modulus of PLLA are improved by the addition of NMMT.(2)Novel bio-based blends of P34 HB and stereocomplex polylactide(sc-PLA)were prepared herein via a simple melt blending method at various sc-PLA loadings at the temperature above the melting points of poly(L-lactide)(PLLA) and poly(D-lactide)(PDLA), and much lower than that of sc-PLA. Wide-angle X-ray diffraction and differential scanning calorimetry results verified that complete stereocomplex crystallites without any evidence of the formation of homocrystallites in the P34 HB melt could be achieved. Scanning electron microscopy observation indicated thatsc-PLA was nicely dispersed in the P34 HB matrix as spherical particles; the dispersed size of the sc-PLA did not display a pronounced increase with an increase in the content of PLLA and PDLA. As solid fillers, sc-PLA could reinforce the P34 HB matrix in a relatively wider temperature region. Accordingly, the rheological and mechanical properties of P34 HB were greatly improved after blending with sc-PLA,particularly when a percolation network structure of spherical filler(a characteristic solid or gel-like structure) had formed in the blends. Moreover, the most intriguing result was that the enzymatic hydrolysis rates had been clearly enhanced in the P34HB/sc-PLA blends than that in the neat P34 HB, which may be of significant use and importance for the wider practical application of biosourced P34 HB. The erosion mechanism of the neat P34 HB and the P34HB/sc-PLA blends was discussed further.