Study On The Crystallizaton Behaviors And Mechanical Properties Of Poly(3-hydroxybutyrate-co-3-Hydroxyvalerate)/Hyperbranched Poly(Ester Amide) Blends

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) is a fully degradable thermoplasticbio-materials synthesized by microorganisms, with great potential advantages such asbiocompatibility, resources renewability. It isn’t produced by using non-renewable resources asraw material, and will not produce secondary pollution to the environment. So it has widelyapplication prospect in agriculture, food and medicine fields. However, the poor thermal stability,narrow processing window and the big and perfect spherulites caused by the high stereo-regularityof PHBV has severely restricted its commercial application. Furthermore, with a low glasstransition temperature of PHBV, the secondary crystallization appears at room temperature, whichexacerbates its mechanical properties. Hyperbranched poly(ester amide)(HBPs) as an amorphousbiodegradable hyperbranched polymer, with irregular stereo-regularity and reactive groups, ismainly applied as modifier for polymer blending.In this paper, PHBV was blended with HBPs by solution coating at various ratios. Thecompatibility, crystallization property, molding process and mechanical properties of PHBV/HBPsblends had been investigated. The research conclusions were as follows:1. The compatibility of two phases in the blends was studied. There were not chemicalreactions between PHBV and HBPs according to Fourier transform infrared spectroscopy (FTIR).But a lot of hydroxyl on HBPs could form the hydrogen with the ester base on PHBV that wouldstrengthen the interfacial compatibility between PHBV and HBPs. The thermal gravimetric analysis results showed that the HBPs had little influence on the thermal degradation temperatureof the blends, and the blends had only one peak which indirectly explained that they had goodcompatibility. The scanning electron microscopy (SEM) photos showed that when the HBPscontent was less than3.5wt%, HBPs could be well-dispersed in PHBV, which had uniform sizeand good compatibility. When the HBPs content exceeded3.5wt%, due to the interaction ofreactive groups in HBPs agglomerating, the interface of HBPs and PHBV phase was very distinctand dispersibility reduced which resulted in phase separation, indicating the incompatibility ofthem.2. Crystallization properties of the blends were researched. The HBPs didn’t change thecrystal structure of PHBV, but reduced the degree of crystallinity of PHBV. The crystalmorphology of PHBV showed that the HBPs destroyed the band structure of the PHBV’ssphaerocrystal and diluted the nuclei of PHBV, resulting in the increase of the PHBV’s spherulitesize. Meanwhile, the interaction between HBPS and PHBV prevented the movement of PHBV. Sothe growth rate of the spherulite decreased. The growth rate of the PHBV’s spherulites had a peakvalue at about90°C. The crystallization kinetics behavior of the blends revealed that thenucleation of pure PHBV was heterogeneous nucleation, and the nucleation of the blends washeterogeneous nucleation. The HBPs increased the crystallization induction period and halfcrystallization time and reduced the rate of crystallization as well as inhibited crystallizationability, which led to increase of the cold crystallization temperature of the blends from45°C to56°C, decrease of the melting point from174°C to170°C and the degree of crystallinity from72.78%to57.34%.3. The molding process and the mechanical properties of PHBV/HBPs blends wereinvestigated. The optimal molding process was the blends blended for4h at56°C. The moldingtemperature, the forming speed and the coating thickness were confirmed as35°C,20mm/s and500um, respectively. Due to the combining effect of the intermolecular forces between PHBV andHBPs, the homogeneous dispersion as well as the deduction of crystallinity, the mechanicalproperties results of the blends showed that the tensile strength and elongation at break of theblends increased at first and then decreased with the increasing added amount of HBPs. When theHBPs content was3.5wt%, compared to the pure PHBV, the tensile strength and elongation atbreak were increased from26.0MPa to28.7MPa and from1.9%to4.3%, respectively.