The crystallization modification of poly（vinylidene fluoride） （PVDF） was investigated for the blend films of PVDF and poiy（methyl methacrylate） （PMMA）. The mass crystallinity （Xc） and further, the β-phase content （F（β）） of PVDF, were studied for the asprepared blend films with different mass ratios. In addition, the variations of Xc and F（β） were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1）Xc, F（β） and even the content of a-phase （F（a）） decreased with the addition of PMMA; 2） with the extraction of PMMA, both Xc and F（β） increased while F（a） decreased. It is worth noting that the increase of Xc and F（β） depended on the relative amount of extracted PMMA （EpMMA）, i.e., the more PMMA was removed, the more Xc and F（β） increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.
Solvent played an important role in the formation of calcium phosphate phase of the chitosan/calcium phosphate composites. In this investigation, ethanolacetic acid mixtures were employed as solvents, and various calcium phosphate phases, such as brushite, amorphous calcium phosphate, and hydroxyapatite, were introduced into the chitosan/calcium phosphate composites by using in-situ preparation process. The results showed that the structures of composite were influenced remarkably by the morphology and the distribution of calcium phosphate phase. In addition, the bioactivity of composites was governed mainly by the characters of calcium phosphate phases in composites, since calcium phosphate phases could induce the growth of hydroxyapatite coating on the surfaces of composites. On the surface of chitosan/brushite composite, the formed hydroxyapatite coating consisted of oriented plate crystallites, which self- assembled into spherical-like crystals. When other calcium phosphate phase was introduced into composites, the polymorphs of hydroxyapatite layer would change greatly. The oriented plate crystallites became bigger, and meanwhile, the self-assembled aggregates became less and smaller. In addition, with the shift of the prior nucleating point, the growth orientation of plate crystallites was transformed.
