Effects Of Chain Branching Based On Hydrogen Bonding On Crystallization Behavior Of Aliphatic Polyesters And Alloys

In order to overcome low crystallization ability of PLA and PBS A,we tried to use PDP as chain branching agents of PLA,PLA/PBSA alloy,PPC/PBSA alloy and PLA/PPC alloy by intermolecular hydrogen bonding to regulate the crystallization behavior.The effect of PDP on the interaction,crystallization behaviors,crystal structure,spherulite morphology and thermal stability of PLA,PLA/PBSA alloy,PPC/PBSA alloy and PLA/PPC alloy were systematically by using FTIR,NMR,DSC,WAXD,POM and TG.Firstly,in order to improve the crystallization ability of PLA,chain branching PLA were prepared chain extension with PDP.The results showed that intermolecular hydrogen bonding occurred between the carbonyl group of PLA and the hydroxyl group of PDP.PLA did not show a crystallization peak,with the increased content of PDP,PLA had a clear crystallization peak,presented that PDP could promote the crystallization of PLA.When the content of PDP reached 25 wt%,the ?Hc was 22.75 J/g.The addition of PDP did not change the crystal form of PLA,but the crystal structure of PLA became loose.When the content of the PDP reached 15 wt%,it could be clearly seen that the spherulite shape presented a significant change from black cross into ring-banded,and the size of the ring-banded spherulites also became larger.The ring-banded spherulites had close relationship with temperature for CB PLA contenting 10 wt%PDP,different spherulites including black cross at 100,110,and 115?,ring-banded spherulites at 120? and larger ring-banded spherulites at 125? could be obtained.And even the ring-banded spherulites disappeared when the temperature rised to 135?.In addition,the addition of PDP reduced the thermal decomposition temperature of PLA from 318?to 261?,but still maintained a high thermal decomposition temperature.Secondly,PDP was selected as chain branching to overcome crystallization behaviors of PLA/PBSA alloy,which was mainly aimed at the poor crystallization of PLA.It could be found that PDP as chain branching was connected to PLA/PBSA alloy by intermolecular hydrogen bonding.The addition of PDP improved the crystallization of PLA.When the PDP content reached 40 wt%,the crystallinity of PLA increased to 19.5%.PDP had little effect on the crystal structure of PLA/PBSA alloy.PLA had the fastest spherulite growth rate of 1.73?m/min at 120?,and the PLA spherulite growth rate in PLA/PBSA alloy was accelerated to 9.10 ?m/min.With the addition of PDP to the PLA/PBSA alloy,the spherulite growth rate of PLA increased to 29.05 ?m/min.In addition,PLA/PBSA alloy changed from one-step thermal weight loss to two-step thermal weight loss after adding PDP.Thirdly,in order to improve the poor crystallization of PBS A in PPC/PBSA alloy,we firstly studied the interaction between PPC and PDP.The results showed that intermolecular hydrogen bonding occurred between PPC and PDP.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.Then,chain branching PPC/PBSA alloy were prepared by intermolecular hydrogen bonding.The chain branching effect greatly improved the crystallization ability of PBSA in the alloy,and the crystallinity was increased from 4.6%to 51.5%.The addition of PDP does not change the crystal form of PPC/PBSA alloy.Finally,chain branching PLA/PPC alloy were prepared by intermolecular hydrogen bonding to overcome the poor crystallization of PLA in PLA/PPC alloy.It could be found that PDP had been successfully connected to PLA/PPC alloy by intermolecular hydrogen bonding.The crystallinity was increased from 4.6%to 51.5%with the addition of PDP content.The growth rate of PLA in PLA/PPC was 4.84 ?m/min,while the pure PLA was 2.51?m/min.The growth rate of spherulite increased with the addition of PDP,and then decreased.When the PDP content was 30 wt%,the spherulite growth rate reached a maximum of 23.88 ?m/min.However,when the PDP content was 40 wt%,the spherulite growth rate reduced to only 16.61 ?m/min.