| Polymer blending is a kind of convenient and effective way of material modification and very important in material processing. Polymer blend films have a wide range of applications in technology and science fields. The performance of polymer blend films depends largely on its morphology.Therefore, understanding the mechanism that controls the film morphology and the physical rules in microstructure will provid theoretical basis for regulating the performance of materials.The poly(3-hydroxybutyrate) (PHB) and poly(propylene carbonate) (PPC)blends were obtained by polymer blending method. The miscibility, crystal behavior, phase separation, and phase structure of PHB/PPC blends were studied.The main work of this paper includes:1. The PHB/PPC blends were obtained by solution casting method.Differential scanning calorimetry (DSC) results indicated that the blends showed miscibility when the PHB content decreased to 10 wt%. The morphology of PHB/PPC (30/70) blend was characterized by Polarized optical micrography (POM), some domains with no birefringence dispered in PHB spherulites. Scanning electron micrography (SEM) results indicated that vertical phase separation took place at 190 ?, most of PPC component migrated to the free surface, and PHB component migrated to the substrate,leading to a PPC-top and PHB-bottom bilayer structure. The microporous in PHB layer were correspond to the domains with no birefringence. After isothermally crystallization, PHB spherulites with microporous can be observed by POM.2. Effects of composition and melting time on the phase structure of PHB/PPC blend thin films were investigated. A low PPC content (e.g. 30 wt %)results in the formation of compact PHB spherulites filling the whole space,whereas the PPC spherical microdomains scatter in the PHB region, and their sizes show a remarkable melting-time dependence. With PPC content increased to 50 wt %, short time at 190 ?, PPC as spheres dispered in PHB continuous phase. With increasing the melting time, it is observed from POM that the separated PHB domains with birefringence scattered in the continuous PPC phase with no birefringence, like parts of a spherulite. SEM results indicated that horizontal and vertical phase separation took place at 190 ?. A large amount of PPC aggregates to the surface forming a network uplayer,whereas the PHB thick domains connected by its thin layer form a continuous PHB region, leading to a superimposed bilayer structure. There is also a small amount of PPC scattered in the PHB domains with birefringence. The PHB thick domains crystallize cooperatively with the PHB-rich sublayer in a same way as the growth of pure PHB spherulites.3. Effects on the band spacing of PHB spherulites were investigated. The band spacing decreased with a small amount of PPC component. And the long period of PHB/PPC blend was larger than that of pure PHB, indicating the partially miscibility of PHB and PPC. Band spacing in PHB/PPC 70/30 blend increased with crystallization temperature. With increasing the melting time,band spacing of pure PHB spherulites firstly increased and then decreased.When the melting time is short than 5 min, the diffusion rate of amorphous component will increase, leading to the increase of band spacing. With prolonging the melting time, amorphous component content will increase because of the degradation of PHB, leading to the decrease of band spacing.Band spacing in PHB/PPC blends increased with melting time. When the melting time is short, PPC molecules maybe selectively adsorb on the folding surfaces of PHB lamellar and cause additional surface stresses to enhance the twisting. And the amount of amorphous component reduced with the melting time, causing the increase of the band spacing. |
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