Fabrication And Properties Of Porous Poly(Propylene Carbonate)

Poly（propylenecarbonate）（PPC）, a new class of biodegradable and environmentallyfriendly polyesters synthesized from propylene oxide （PO） and carbon dioxide（CO₂）,showsexcellent biodegradability,toughness and acoustic insulation.Nowadays, the thinfilms of PPChas widely used in industry and agriculture.Porous material has attracted much attentionowing to its advantages of lightweight, cushioning performance and cost reduction.Whilepoor foam properties, thermal properties,mechanical strength,lack of study on PPC porousmaterial might be obstacles for its broad applicatons such as acoustical material,packing andfilling material.To solve the above problems, PPC/nano-CaCO₃composites which have better tensileproperty and thermal stability were prepared,then a study of batch foaming with supercriticalcarbon dioxide was conducted.Finally, PPC/nano-CaCO₃microcellular foams withinterconnected pore structures or lower pore diameter and higher pore density were prepared.In this paper, PPC/nano-CaCO₃composites at different nano-CaCO₃contents wereprepared with novel triple screw extruder.Then tensile properties,thermal properties,melt strength andviscosity were studied.The result suggested that mechanical properties,thermal properties and meltproperties of the composites became better after nano-CaCO₃incorperation.The optimum tensilestrength increased by8.73%coMPared with that of pure PPC when the nano-CaCO₃was3wt%,andelongation at break only showed a slight decrease.Also thermal properties of nanocompositesincreased,which tended to stability while nano-CaCO₃content exceeded3wt%.The optimumglass-transition temperature and extrapolated initial decomposition temperature increased by1.5℃and17.8℃respectively when nano-CaCO₃content was10wt%.The melt strength andviscosity showed an increase with bigger nano-CaCO₃content.On the basis,the effect of different foaming process parameters on the foam propertiesof pure PPC was investigated.The result suggested that saturated temperature and saturatedpressure were key factors.The foam with small size（average pore diameter0.92um） and highpore density(5.61×10¹⁰cell/cm³) was fibricated at20MPa and50℃for4h.Then the effect ofsaturated temperature and nano-CaCO₃content on the foam properties of PPC/nano-CaCO₃ composites was studied.The result revealed that nano-CaCO₃could improve the pore connectivityand morphology under proper foaming condition.The optimum foam property with with smallsize（average pore diameter0.55um） and high pore density(1.73×10¹¹cell/cm³) was obtainedwhen nano-CaCO₃content was10wt%at20MPa and50℃for4h.The prepared microcellularfoams included semi-closed-cell foam（more bubble coalescence and interconnected porestructure） and closed-cell foam（lower pore diameter and higher pore density）,and the formercould be used for acoustical material because of its good sound-absorbing performance in thelow frequency range,while the latter might have a promising market of packing and fillingmaterial due to its better mechanical properties.