Research On The Modification Of Biopolymer Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) is a kind of thermoplastic material synthesized by microbial fermentation, It has a nice biodegradability and some special properties such as gas barrier property and uvioresistant. The advantages of PHBV make it potential to be a kind of environmental friendly material, which can be used as a substitute for the existing plastics. However, compared with the general plastic, the application of PHBV is seriously restricted by its disadvantages, such as poor thermal stability, narrow melt processing window, high crystallinity, and fragility. In this paper, two different composites PPG/PHBV and PPG/OMMT/PHBV were made firstly by adding polypropylene glycol (PPG) and/or octadecylamine-modified montmorillonite (OMMT) with the solution mixing method, the crystallinity, thermal stability, compatibility, mechanical property of the blends were discussed and studied by differential scanning calorimetry (DSC), thermogravimetry analysis (TG), polarizing optical microscopy(POM), scanning electron microscope(SEM), X-ray diffraction measurements(XRD), dynamic contact angle test, and tensile test, respectively.Firstly, the influence of PPG and OMMT composition on the property of the binary and ternary blends were studied. The experimental results showed that both of the blends were compatible, and the addition of the second and third component changed the blend properities obviously.For the PHBV/PPG binary blends, the melting temperature was decreased and the degradation temperature was increased with the addition of PPG, therefore the processing window was broadened. At the same time, PPG also caused the decrease of the crystallinity, thus the elongation at break of the binary blends was improved much, and their plasticity were increased, but their tensile strength was decreased obviously. The best performance of the blends was found when the PPG with Mw 1000 was used and theweight ratio of PPG was 20%. Compared with pure PHBV, their initial decomposition temperature and the decomposition temperature could been increased by 25.88℃ and 15.36℃, respectively, the elongation at break could been increased by 415.23%, and the tensile strength was decreased by 69.31%. As for the PHBV/PPG/OMMT blends, the distance between the silicate layers increased from 1.2nm to 3.18nm after the MMT modified with SDS, and the PHBV could be the coexistence of intercalated and exfoliated states in the produced nanocomposites. Along with the increase of OMMT in the ternary blends, the thermal stability of the nanohybrid-materials increased firstly and then decreased. It was also found that the tensile strength of the ternary blends could be increased with the addition of OMMT, however, the elongation at break was just decreased a little.When the weight ratio of OMMT was 3%, the ternary blends showed the best properties. Compared to the binary blends, their crystallinity and the initial thermal decompositon temperature could been increased by 37.86% and 12.5℃ respectively, thus the temperature of their process window could be increased from 112.4℃ to 124.67℃. It was also found that the tensile strength of the ternary blends could be increased by 34.44% and the enlongation at break was decreased by 32.34%.Secondly, the degradability of PHBV/PPG and PHBV/PPG/OMMT blends were studied in this paper. The experiment results showed that PPG acted as diluent, which could reduced the degree of crystallinity of system and led to the faster degradation of PHBV. It was also found that the addition of OMMT could improve the crystallinity of the blends, and the intercalated structure of OMMT also could decrease the contact area of PHBV in soil suspension. Both of them made the degradation rate of ternary blends decreased. When the two different blends PHBV/PPG and PHBV/PPG/OMMT were degraded in soil suspension after 4 weeks, the weight loss of PHBV/PPG and PHBV/PPG/OMMT (OMMT 3%) blends was 35.4% and 30.1% respectively.