Study On Preparation And Performance Of Bio-based Polyurethanes

The raw materials of traditional synthetic polyurethane are almost from non renewable petroleum resources.Because of the increasing depletion of oil resources and the material is very difficult to be degraded under natural conditions,it can cause serious energy waste and environmental pollution.Therefore,it is urgent to solve the problem of seeking new resources.It has important practical significance for the synthesis of environmental friendly and biodegradable green economic polyurethane,which can replace petrochemical products with the abundant vegetable oil and the biodegradable poly lactic acid.Vegetable oil is cheap,renewable resources,and has the advantages of biodegradable,low toxicity and high purity;poly lactic acid(Polylactide PLA)is a biodegradable polymer,thermoplastic and easy processing.The synthetic raw material of lactic acid is come from natural renewable resources-starch fermentation,which has important significance for sustainable development.This thesis mainly includes the following three aspects of the research content:1)A new linear 10-undecenoic acid-based diol and three chain extenders with different dangling chain lengths were synthesized via thiol-ene coupling and esterification reaction.A series of polyurethanes with different dangling chain length and content prepared by copolymerization with HDI.We have investigated the effect of dangling chain length and content on thermal properties and crystallization properties of 10-undecenoic acid-based polyurethanes.Research results show that the dangling chain length and content have no significant effect on the thermal stability performance of the polyurethane.With increasing chain length and content of the dangling chains,the Tg and Tm of the polyurethanes decreases.And the dangling chain reduces the crystallinity of polyurethane.2)Polylactide polyol(PLA-OH)and poly(lactide-co-caprolactone)polyol(P(LA-co-CL))were polymerized with different isocyanate compounds which is Toluene diisocyanate(TDI),Hexamethylene diisocyanate(HDI)and Diphenyl methane diisocyanate(MDI)respectively to prepare a series of biodegradable polyurethanes.We studied the effect of the molecular weight of the polyol,the type of isocyanate and the type of the polyol on the thermal performance and mechanical properties of the polyurethane elastomers.The glass transition temperature of the polylactic acid based polyurethane is between 15-55?.Thermal decomposition temperature of the polyurethanes elastomers is above 200?.The tensile strength of MDI-based PUs is about 23.5Mpa.And elongation at break of the polyurethanes is more than 400%,the mechanical properties close to oil-based polyester type polyurethane Bayer Desmopanò400 series.3)In this work,a series of IPDI-based shape memory polyurethanes were synthesized from polylactide copolymer diols,isophorone diisocyanate(IPDI)and chain extenders.These bio-based Polyurethanes show a T_g in the range of 28-54~°C,which is very closed to body temperature and influenced by the carbon chain length of the chain extenders.The tensile strength of IPDI-based PUs is between2.3-3.5Mpa.And elongation at break of the polyurethanes is more than 350%.Through a serial of shape memory tests,the IPDI-based shape memory polyurethanes exhibit good shape memory behavior at body temperature with greater than90%shaperecoveryrate.Especially,thebio-PUfrom1,4-cyclohexanedimethanol(CHDM)with non-planar ring structure displays highest shape recovery rate,which may due to that CHDM in the hard segments acts as“molecular spring”.Therefore,these shape memory bio-PUs are expected to have many practical applications in medical devices.