Structure And Properties Of Poly(propylene Carbonate) Composites Prepared By Melt Blending And Microlayer Co-extrusion

Poly(propylene carbonate)(PPC) is one of carbon dioxide sourced environmental friendly thermoplastic aliphatic polycarbonate, and it has a good gas barrier property. However, PPC shows poor mechanical properties and thermal stability, which limits its practical application in the area of packing materials. In this work, composites based on poly(propylene carbonate) were prepared by melt blending and microlayer co-extrusion to improve its mechanical, thermal and barrier properties.Considering that hydrogen bonding interaction between polymer and polymer or fillers can improve properties of composites, PPC/thermoplastic starch(TPS), PPC/thermoplastic oxidized starch(TPOS) and PPC/AL-TPOS(TPOS modified by aluminate coupling agent) blends were prepared by melt blending. FTIR results showed that there existed hydrogen-bonding interaction between PPC and three types of modified starch, and oxidation of starch changed hydroxyl groups of starch into hydrophobic carbonyl groups, enhancing the hydrogen-bonding between PPC and starch. SEM observation revealed that the compatibility and interfacial interactions between PPC and TPOS were improved by the oxidation of starch. As a result, PPC/TPOS composite showed a better performance in storage modulus, loss modulus, complex viscosity, tensile strength and thermal properties compared with PPC/TPS composite. Furthermore, the modification of TPOS by aluminate coupling agent(AL) facilitated the dispersion of oxidized starch in PPC matrix, and resulted in the increasing of tensile strength and thermal stability. For PPC/AL-TPOS composites, the tensile strength and glass transition temperature(Tg) increased first with the adding of AL-TPOS. However when the content of AL-TPOS increased to 50 wt%, the tensile strength decreased. In addition, the addition of hydrophilic starch increased the water absorption capacity of PPC, and then it weakened the water vapor barrier property.PPC/PVA blends and PPC/(PPC/PVA) microlayered composites were prepared through melt blending and microlayer co-extrusion in order to improve both mechanical and barrier properties of PPC. For PPC/PVA blends, effects of PVA content on morphology, rheological behavior, mechanical properties and barrier properties of blends were investigated. Results of SEM and rheological behavior revealed that a good compatibility and interfacial interactions existed between PPC and PVA. Therefore, the tensile strength of PPC/PVA blends increased with the increase of PVA content, and the elongation at break of all samples were higher than 400%. Moreover, the homogeneous distribution of PVA in the PPC matrix extended the diffusion path of oxygen molecule in the blends, and enhanced the oxygen barrier property of PPC. But the incorporation of hydrophilic PVA decreased the water vapor barrier property of PPC. For PPC/(PPC/PVA) microlayered composites, the stable lamellar morphology and good bonding strength between the layers endowed microlayered composites with good tensile strength and elongation at break. Particularly, PPC, as the outer layer of the microlayered composites, effectively reduced water absorption capacity of PVA, and resulted in a better water vapor barrier ability compared with PPC/PVA blends.Considering that lamellar structure can greatly enhance mechanical and barrier properties of composites, PPC/Poly(lactic acid)(PLA) microlayered composites and PPC/PLA blends were fabricated via microlayer co-extrusion and melt blending respectively. The phase morphology, interfacial interaction, mechanical and barrier properties were studied by means of SEM, dynamic rheological measurement, tensile test and gas transmittance test. Results of mechanical properties showed that the alternating distribution of layered PLA endowed a higher tensile strength of PPC/PLA microlayered composites than that of the blends. Increasing the number of layers could improve the elongation at break for PPC/PLA microlayered composites. This was because when number of layers increased, the interface delamination could absorb more tensile energy and PLA layers would displayed a discontinuous morphology,which led to the decrease of the brittle failure. Results of gas transmittance tests revealed that both oxygen permeability and water vapor permeability of PPC/PLA microlayered composites were much lower than that of the blends, and a further improvement in the barrier properties could be achieved by increasing the number of layers. What’s more, increasing the number of layers could reduce the damage of the rising temperature on the barrier properties of PPC/PLA microlayered composites. It was because PLA worked as rigid layers in the microlayered composites, and limited the movement of the PPC chain as well as the increase of free volume, making the permeation of small molecules in the PPC become more difficult.