Preparation And Properties Of Chlorinated Poly(Propylene Carbonate) And Its Composites

Poly(propylene carbonate),an alternating copolymer of carbon dioxide and propylene oxide,is a typical biodegradable material and has attracted much attention because of its good gas barrier property,high transparency and reasonable melt processibility.Although PPC has been put into the stage of industrial production,it has some performance defects,such as large brittleness at low temperature,poor dimensional stability at high temperature and sensitivity to heat,which limit its extensive application.In this dissertation,PPC was chlorinated for the first time in our laboratory to enhance its performance.The newborn polymer material was named as chlorinated poly(propylene carbonate)(CPPC).The structure and properties of CPPC were investigated in detail.Moreover,the polymer composites based on CPPC were prepared to endow CPPC with new functions,which could greatly broaden its applications.Details of the research contents and the results are summarized as follows:1.Preparation of chlorinated poly(propylene carbonate)through gas-solid chlorination and its properties:CPPC with chlorine content of 1.7 wt%was prepared for the first time by gas-solid chlorination reaction.It was noted that the reaction conditions of the chlorination of PPC were quite mild,which could be easily and simply realized at industrial level.NMR spectroscopy showed that the chlorination reaction mainly takes place between chlorine and—CH3 of PPC,forming new groups—CH2Cl and—CHCl2.The influence of chlorination modification on properties of CPPC was then investigated.It was found that the introduction of chlorine atoms could further improve the superior properties of PPC,such as biodegradability and gas barrier.Moreover,compared with PPC,CPPC possessed many more distinguished properties in solubility,wettability,and adhesive.All these distinguished properties can greatly broaden the applications of CPPC in the fields of coating,ink,adhesive,barrier materials and so on,which could greatly promote the development of PPC industry.2.Preparation of chlorinated poly(propylene carbonate)through water phase suspension chlorination and its compatibilization:CPPC with chlorine content of 5.0 wt%was successfully prepared through water phase suspension chlorination.The prepared CPPC was then melt blended with maleic anhydride-end-capped PPC(PPC?MA)and thermoplastic starch(TPS)to investigate the effects of CPPC on the compatibility,rheological and mechanical properties of PPC-MA/TPS blends.It was found that CPPC could enhance the interaction between PPC-MA and TPS.Therefore,moderate addition of CPPC could efficiently improve the compatibility of PPC-MA/TPS blends and a perfect co-continuous structure was formed.Rheological investigation revealed that the blends with CPPC exhibited a non-terminal behavior at low frequencies and a pronounced shear thinning behavior at high frequencies.Moreover,tensile strength,elongation at break and Young's modulus of the blends simultaneously increased to peak values with increasing the CPPC content up to 5.0 wt%,thereafter they reduced with further increasing the CPPC content.3.Preparation of carbon black/chlorinated poly(propylene carbonate)foams with negative temperature coefficient effect of resistance:Carbon black/chlorinated poly(propylene carbonate)(CB/CPPC)foams with a well-defined close-celled structure were fabricated by the combination of the facile melt blending and the subsequent chemical foaming process.It was found that the foaming treatment could significantly lower the electrical percolation threshold from 2.48 vol%(solid composites)to 0.138 vol%.More interestingly,it was noted that the CB/CPPC foams exhibited a nearly-linear negative temperature coefficient(NTC)effect of resistance with increasing temperature from 25?C to 70?,which was attributed to the gas expansion-induced thinning of cell walls and thereby decreasing the distance between the adjacent CB particles.Compared to the previous literatures,the CB/CPPC foams exhibit higher NTC sensitivity than most of the previous NTC CPCs.Moreover,it is observed that the crosslinked CB/CPPC foams have both high sensitivity and good reproducibility of NTC effect,which have the potential applications in the wearable electronics and temperature sensors in medical,food,and environment monitoring.4.Light-actuated shape memory and self-healing properties of carbon nanotubes/chlorinated poly(propylene carbonate)composites:The composites with light-actuated shape memory and self-healing properties based on CPPC and multi-walled carbon nanotubes(MWCNTs)were fabricated by a facile melt blending.It was found that the shape memory behaviors of MWCNTs/CPPC composites could be triggered not only by IR light but also by natural sunlight.Under natural sunlight irradiation,the recovery time of the composite is only 39 s.However,the light-actuated shape memory behavior is irreversible.We further fabricated MWCNTs/CPPC-paper bilayer composites,which are able to achieve the reversible shape changes controlled by light irradiation.Based on the bilayer composites,we designed an artificial flower which could automatically open under sunlight and close after blocking the sunlight,just like the heliophile flowers in nature.Moreover,the MWCNTs/CPPC composites also exhibited rapid and efficient self-healing behaviors under light irradiation.The healed sample can roughly maintain its Young's modulus and electrical conductivity after IR-induced self-healing.Considering the excellent conductivity,light-actuated shape memory and self-healing properties,the MWCNTs/CPPC composites may have great potential in soft robotics,biomimetic and solar devices.