Effects Of Hydrogen Bonding On Crystallization Behavior Of Aliphatic Polyesters

The crystallization behavior and crystalline structure of PBSA/PDP supramolecular complex formed by self-assembly via hydrogen bonding were investigated. Analyses combined FTIR and 13C NMR confirmed the formation of intermolecular hydrogen bonding between hydroxyl group of PDP and carbonyl group of PBSA, which linked PDP to PBSA as side chain. The results by DSC indicated that the formation of hydrogen bonding led to retarded crystallization of PBSA and reduced lamellar thickness. Confined crystallization and melting of alkyl chains in PDP molecule occurred during cooling and heating DSC scans, accompanied with heat absorption or release. The melting point and crystallization temperatures increased with PDP content, which was interpreted as increasing alkyl chain length involved in confined crystallization. The crystalline structure of alkyl chains in PDP molecule were identified using WAXD as orthogonal phase (βo). TG analysis suggested that the thermal stability of complexes decreased with PDP incorporation. It can be inferred from the above results that PBSA/PDP complexes can potentially serve as phase change material.The effects of hydrogen bonding on crystallization behavior, crystal structure and crystal morphology of PBSA/TDP complexes were systematically investigated. The formation of hydrogen bonding between carbonyl group of PBSA and hydroxyl group of TDP was verified FTIR analyses. The fraction of hydrogen bonded carbonyl groups in PBSA increased with TDP addition. Non-isothermal crystallization and melting peak temperature of PBSA decreased, while t1/2 derived from isothermal crystallization analyses increased with TDP addition, implying that crystallization of PBSA was impeded by TDP addition. PBSA crystallites assume a two dimensional to three dimensional growth with a combination of homogeneous and heterogeneous nucleation. Analysis based on Lauritzen-Hoffman theory indicated that the fold surface free energy (σe) and work of chain folding (q) of PBSA chain increased with TDP addition. POM observation exhibited concentric ring-banded spherulites for samples with 10 and 20 wt% TDP. A peculiar ring-banded pattern with discrepant band spacing was obtained for the first time by addition of 30 wt% TDP, whose formation mechanism remains to be discussed.The effects of hydrogen bonding between PLLA and TDP on crystallization behavior, crystal structure and lamellar organization of PLLA were studied. The results suggest that TDP was linked via intermolecular hydrogen bonding and existed in amorphous state in PLLA matrix, which decreased the mobility of crystallization of PLLA chains and resulted in reduced Tg, crystallization and melting temperature. The isothermal crystallization of PLLA/TDP comlexes assumed three dimensional crystal growth with heterogeneous nucleation, while crystallization rate decreased by TDP addition. Analysis based on Laurizten-Hoffman theory indicated that the values of σe and q increased with TDP addition. The long period of PLLA was increased by TDP incorporation as evidenced by SAXS analysis, meaning more amorphous component existing between adjacent lamellae.Amorphous PVPh was introduced into PBSA/PLLA blends via intermolecular hydrogen bonding interaction to study its influence on miscibility and crystallization of PBSA/PLLA blends. FTIR verified intermolecular hydrogen bonding between PVPh and PBS A and PLLA. The miscibility between PBSA and PLLA were improved with PVPh introduction evidenced by approaching Tgs of the two components in DSC analyses. When PVPh content reached up to 50 wt%, the blend sample exhibited only one Tg, meaning complete miscibility between PBSA and PLLA. The improved miscibility of PBSA/PLLA blends was further confirmed by SEM. Typical "sea-island" phase separation structure for PBSA/PLLA blend transformed into one phase structure for PBSA/PVPh/PLLA blend samples. In addition, the melt crystallization temperature of PBSA in blend samples decreased with PVPh addition, while that of PLLA remained almost unchanged. Avrami analyses suggested that crystallization of PBSA in blend samples assumed two to three dimensional crystal growth with a combination of homogeneous and heterogeneous nucleation, while that of PLLA assumed three dimensional crystal growth with homogeneous nucleation. Crystallization rate of PBSA was distinctly decreased by PVPh incorporation. In contrary, crystallization of PLLA increased slightly with PVPh addition. The crystal structures of PBSA and PLLA were not modified by PVPh incorporation.