Preparation And Enzymolysis Properties Of Bio-based Thermoplastic Polyurethane Elastomers

Biomass resources exist widely in nature but lack of systematic utilization and development.Polyurethane material is the fifth largest synthetic material in the world and will be in great demand in the Chinese market in the future.The preparation of high-performance polyurethane elastomers with bio-based materials is of great significance to promote the green and sustainable development of polyurethane industry.Conventional polyurethanes have low molecular chain flexibility under traditional degradation conditions,resulting in poor degradation performance.In this paper,a kind of bio-based polyester diol with low glass transition temperature and high flexibility was prepared by bio-based small molecule diacids and diols.And These bio-based polyester diols were introduced into bio-based thermoplastic polyurethane(BTPU)molecular chain to improve the flexibility of BTPU and enhance its degradation ability.The enzymatic degradation experiments of BTPU were carried out at high temperature to achieve the rapid degradation of BTPUs because BTPU is more flexible at high temperature.In this paper,we studied the effects of different soft segment molecular weights and hard segment contents on the microstructure,mechanical properties,thermal properties and degradation properties of BTPU,which provided a reference for the research and development of biodegradable polyurethane elastomers.Firstly,in chapter 3,linear random polyester diols were synthesized from succinic acid,sebacic acid,propylene glycol,2,3-butanediol of biological origin.And polyester polyols with molecular weights of 2000,4200,5660 g/mol were obtained by adjusting the polycondensation time.Proton nuclear magnetic resonance and Fourier Transform infrared spectroscopy showed that the three polyester diols with different molecular weight shared similar chemical composition.Differential scanning calorimetry showed that these bio-polyester diols had low T_gvalues.All these works made a good preparation for the synthesis of BTPUs with high properties.Then,in chapter 4,BTPUs with different soft segment molecular weights and hard segment contents were prepared by using bio-based polyester diols with low T_gvalues as the soft segment.Atomic force microscopy was used to study the microphase separation of BTPUs.As the result of this,correlation between microstructure and macroscopic properties was made.Furthermore,we constructed the structure-activity relationship between soft molecular weight,hard segment content and the mechanical properties,thermo-mechanical properties and heat resistance of BTPUs.The high toughness BTPU with the best elongation at break up to2000%and the high strength BTPU with the best strength up to 19.6 MPa were prepared.Finally,in Chapter 5,High temperature stable keratinase LCC was used as hydrolysis catalyst to degrade BTPUs.The structure-activity relationship between the chemical structure of bio-based polyurethane and its degradation ability in enzyme solution was established by tracking the mass loss of BTPUs during the degradation process and the change of the chemical structure and morphology of the samples before and after degradation.The most degradable sample 2000-15%had a degradation rate of 89.6%after 12 days of degradation.