Properties Study of Thermoplastic Elastomers Prepared by Sequential Ring-opening Copolymerization of Bio-based δ-Caprolactone and L-lactide
It is of significance to develop renewable and biodegradable aliphatic thermoplastic elastomers,which are promising replacement of the widely used polystyrene-based thermoplastic elastomer materials and are expected to partially address the end-of-life issue of plastics.Poly(lactic acid)-b-poly(δ-caprolactone)-b-poly(lactic acid)triblock copolymer was successfully prepared by sequential ring-opening copolymerization of commercial bio-based δ-caprolactone and L-lactide in the presence of an organobase(t-BuP2)/urea as binary catalytic system.These triblock copolymers exhibited different microphase separation structures and mechanical properties depending on the composition of soft and hard segments.As the volume fraction of the hard segment(fhard)increased from 0.22 to 0.34,the microphase separation structure of the sample gradually changed from spheres to hexagonally packed cylinders,and finally to lamella.Whenfhard was in the range of 0.30-0.45,the triblock copolymers behaved as thermoplastic elastomers(TPEs)with high elongation at break(εb=600％-1000％)and good tensile strength(σb=10-20 MPa).The samples with fhard～0.35 exhibited high elastic recovery(ER～90％),high resilience(～70％)and low residual strain(＜10％).When the samples possessed comparable molecular weight of soft segment,the elastic recovery and resilience gradually decreased while the residual strain increased as fhard decreased from 0.34 to 0.22.The triblock copolymers that possessed a relatively lower volume fraction of the hard segment(fhard＜0.22)can be used as pressure-sensitive adhesives after mixing with epoxy soybean oil(ESO).The 180° peel strength of PSA can be further adjusted by changing the composing triblock copolymers and the ratio of copolymers to ESO.The 180° peel adhesion tests showed that the peel strength of PSA-1 was(3.0±0.4)N/cm,and that of PSA-2 was(0.3±0.05)N/cm,which can be used as kraft paper tape and post-it note,respectively.
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