Preparation And Characterization Of Biodegradable Composite For PLA/PBAT Foaming

With the rapid development of the logistics industry,a large amount of waste foam materials are generated from goods packaging.Currently,widely used foam materials are non-degradable and can only be disposed by incineration or landfills after disposal,causing environmental pollution and energy waste.Therefore,they are often compounded to complement each other.Both PLA and PBAT are prone to collapse during foaming due to their straight-chain structures with low intermolecular chain entanglement and weak viscoelasticity.In this paper,PLA/PBAT blends were modified by fixing mass ratio of PLA/PBAT with multi-reactive epoxy chain extender,multi-reactive anhydride chain extender and epoxy/anhydride combination chain extender as topologically branched chain extenders.The reaction mechanism of the chain extender and its effect on the system properties were investigated by characterizing the acid value,characteristic viscosity,thermal properties and rheological properties of the system,and the changes of the foaming properties of the system before and after the modification were investigated by extrusion foaming method.In order to clarify the structure,intrinsic reactivity and thermal stability of the modified materials,the PBAT copolymer structure,the degree of reaction during the melt blending of PLA and PBAT,and the degradation behavior of both polymers during processing at high temperature were investigated.BT:BA segment ratio in PBAT was calculated as 48:52 based on nuclear magnetic hydrogen spectroscopy.Combined with the SEM cross-sectional morphology and structural analysis,after melt blending of PLA and PBAT,the two were only physically intermixed,rather than chemical bonding.The thermal degradation of PLA and PBAT was investigated by rotational rheometer processing and twin-screw extrusion.the intrinsic viscosity of PLA decreased significantly with the increase of processing time,rotor speed and processing temperature.While the intrinsic viscosity of PBAT showed fluctuating changes,indicating that the thermal processing stability of PBAT was better than that of PLA.In the twin-screw blending experiment,the thermal performance indexes of PLA such as T_g,T_cc and T_m did not change significantly when the processing temperature increased from 190℃to200℃.In order to explore the effects of different chain extenders on the properties of PLA,PBAT,and PLA/PBAT,triglycidyl isocyanurate（TGIC）,3,3′,4,4′-Biphenyl tetracarboxylic diandhydride（BPDA）,and their composite TGIC/BPDA were used as chain extenders.Reactive extrusion modification of the PLA,PBAT and PLA/PBAT（70/30）blends were conducted using a twin-screw extruder,and the modified materials’end carboxylic groups,chemical structure,thermal properties,crystal structure,and melt viscoelasticity were characterized.The results showed that:TGIC reacts with the terminal carboxy group,resulting in lower acid value,higher characteristic viscosity（[η]）,energy storage modulus（G′）,loss modulus（G″）and complex viscosity（η^*）of PLA,PBAT and PLA/PBAT systems,and improving rheological properties.BPDA reacts with the hydroxyl group and produces new carboxyl groups,resulting in higher acid value,lower[η],G′,G″andη^*of PLA,PBAT and PLA/PBAT systems,and weakening rheological properties.PLA/PBAT system with TGIC/BPDA composite chain expansion shows outstanding rheological performance.The energy storage modulus of the system increased and the entanglement of molecular chains intensified after adding PBAT to PLA.The crystallization ability of the PLA system decreased after adding TGIC for chain extension modification,while the crystallization ability of the PBAT system increased after modification.PLA shows more great effect on properties of modified PLA/PBAT,and the crystallization ability is thus weakened.The TGIC/BPDA composite cross-linking agent has improved the various rheological properties of PLA,but weakended the rheological properties of PBAT.When the PLA/PBAT blend system is modified with the composite cross-linking agent,the rheological behavior of the sample shows the characteristics of a topological branched system,and the branching effect is supervior than that of modified by only TGIC or BPDA.In order to explore the foaming properties of the chain-extended PLA/PBAT composite,the foaming process was studied and optimized.Technology with high foaming magnification,small and dense pores were selected for preparation.Specifically,the experimental conditions were determined as twin screw processing at 190℃and adding 3%of foaming agent,and the foaming properties of the PLA/PBAT before and after modification were analyzed.The results showed that the foaming properties of PLA/PBAT were improved after single-chain extender TGIC or BPDA modification.The foaming and mechanical properties of the samples after TGIC/BPDA two-step chain extension were better.Compared with the PLA/PBAT sample without modification,the bubble density of samples with TGIC/BPDA topological chain expansion was increased by 172%,while the bubble diameter decreased by 28%with an elastic modulus of 199MPa.In this paper,based on the principle of topological chain expansion modification,TGIC and BPDA were used as chain expansion agents to modify PLA/PBAT biodegradable composite.Effects of single TGIC and BPDA chain expansion and TGIC/BPDA composite chain expansion reaction on the rheological properties and the spontaneity of the blended system were investigated,which can provide reference for the subsequent research of modified foams of biodegradable materials.