Study On Preparation,Structure And Properties Of High Heat-resistance Thermoplastic Polyurethane Elastomer

Tires are the most consumed rubber products.The tire wear and unrecyclable waste tires will cause environmental pollution.For a real application,rubber materials for tires need to be vulcanized and reinforced.Rubber materials have the drawbacks that they are difficult to be recovered after vulcanization and the rolling resistance increases after reinforcement.Thermoplastic polyurethane elastomer(TPU)has the advantages of excellent structural designability,high mechanical strength,wear resistance,recyclability,and low rolling resistance.It can be used as a promising tire material.However,the insufficient heat resistance hinders the application of polyurethane,especially for TPU with only physical cross-linking,temperature of long-term of use for polyurethane generally cannot exceed 80?,which limits the application of TPU as tire material.Changing hard segment content and the type of chain extender are the main methods to improve the heat resistance of TPU.Among various diisocyanates,the toluene diisocyanate(TDI)and diphenylmethane diisocyanate(MDI)are the most widely used.However,there are isomers of TDI and isocyanates in MDI are not in the same plane due to methylene,thus,regularity of the hard segment and the heat resistance of TPU are not high enough.At the same time,the dynamic heat generation of MDI and TDI based TPU is high due to the asymmetric structure,which also limits the application of TPU as tire material.In order to improve the heat resistance of TPU,meet the requirement of material for tire,expand the application scope of TPU,the symmetric and rigid 3,3'-dimethylbiphenyl-4,4'-diyl diisocyanate(TODI),1,4-Phenylene diisocyanate(PPDI)and 1,5-naphthalene diisocyanate(NDI)and a new chain extenter with urethane bond are specially chosen to synthesize TPU with regular hard segment and excellent head resistance.The problem of low wet skid resistance of TPU as a tire material can be solved by changing the type of soft segment after meeting requirement of heat resistance.In Chapter 3 of this paper,TODI with biphenyl structure and high rigidity,1,4-butanediol(BDO)and poly(tetramethylene ether)glycol(PTMG)were used to synthesize TODI-based TPU(TODI-TPU).The effects of different average hard segment length and soft segment molecular weight on the performance of TODI-TPU were studied.All TODI-TPUs have micro-phase separation structure.When the average hard segment length increases or the soft segment molecular weight decreases,the percent of hydrogen-bonded carbonyl,degree of hard segment crystallization,melting temperature of hard segment,softening point temperature,tensile strength and thermal weight loss in the first stage of PPDI-TPU increases.The heat resistance of TODI-TPU is higher than that of MDI,TDI and HDI based TPU at the same molar ratio.3D printing is an important method for preparing non-pneumatic polyurethane tires,the possibility of TODI-TPU used as the raw material of 3D printing was also studied in this chapter.The results showed that TODI-TPU can be prepared into wire for 3D printing.It is expected to use 3D printing technology to prepare 3D printed polyurethane tires of TODI-TPU and can enrich range of the raw materials with high heat resistance for 3D printing.In Chapter 4 this paper,PPDI with higher isocyanate content than TODI and MDI and higher symmetry than TODI,PTMG and BDO were used to prepare PPDI-based-TPU(PPDI-TPU)with low hard segment content and high heat resistance.The effects of different average hard segment length and soft segment molecular weight on the performance of PPDI-TPU were systematically studied.The results show that all PPDI-TPU samples have micro-phase separation structure;the average hard segment length and soft segment molecular weight can be used to adjust the heat resistance of PPDI-TPU.When the average hard segment length increases or the soft segment molecular weight decreases,the softening temperature and the percentage of hydrogenated carbonyl groups of PPDI-TPU increase.The heat resistance of PPDI-TPU is better than that of MDI,TDI and HDI based TPU at the same molar ratio.Compared to MDI,TDI and HDI based TPU,the softening point temperature of PPDI-TPU is increased by 9.5%,23.1%and 58.6%respectively.The softening point temperature(187?)of PPDI-TPU with hard segment content of 15%is also higher than the softening point temperature(183.6?)of the TODI-TPU with hard segment content of 24%.PPDI can be used to synthesize TPU with low hard segment content and high heat resistance.In Chapter 5 of this paper,NDI with higher symmetry than TODI and greater rigidity than PPDI is used as part of the hard segment to further improve the heat resistance of the TPU.NDI,PTMG and BDO were used to synthesize NDI-based-TPU(NDI-TPU).The effects of soft and hard segment composition on the performance of NDI-TPU were systematically studied.The results show the higher heat resistance of TPU can be synthesized by diisocyanate with greater rigidity.The heat resistance of NDI-TPU is 10%,23%,35%,52%and 86%higher than TODI,PPDI,MDI,TDI and HDI based TPU with the same molar ratio.The formula ratio with the best overall performance is selected,then different soft segments were used to adjust the wet skid resistance of NDI-TPU.The results show NDI-PCDL from polycarbonate diol(PCDL),NDI and BDO,the molar ratio of those are 1:1.5:0.5 possesses excellent properties,the loss factor of NDI-PCDL is 0.421 at 0?,which has very good wet-skid resistance.The loss factor is only 0.046 at 60?,which has very low rolling resistance.The elongation at break and tensile strength of NDI-PCDL were 467%and 43.6 MPa,respectively.Compared with the commercial green tire compound(HT166),rolling resistance of NDI-PCDL was reduced by 64%,wear resistance of NDI-PCDL was increased by 84%,and tensile strength of NDI-PCDL was increased by 136%.Softening point temperature of NDI-PCDL was 204?,and heat resistance of NDI-PCDL is 21%,9%,and 10%higher than those of commercially available HPM-C85A(BASF),PR860(LANXESS),and Desmopa 8785A(Covestro)samples,respectively.The heat resistance of NDI-PCDL meets requirements of the automobile tire,and it is expected to meet the requirements of high wet skid resistance,low rolling resistance and high wear resistance in the tire at the same time,thus it can be a promising next-generation material for high-performance automobile tire.The chain extender is another part of the hard segments.Common diol chain extenders do not contain urethane bonds.In the sixth chapter of this thesis,a chain extender containing urethane bonds is synthesized by ring-opening polymerization of hexamethylenediamine(HDA)and ethylene carbonate(EC),and experiments are designed to study effect of hard segment length distribution on heat resistance of TPU.Compared to TPU with polydispersed hard segment length,the microphase separation and performances of TPU can be improved by using the hard segment with the equal-length.The hard segment dispersion and size are more uniform,heat resistance and mechanical properties are increased by 17%and 77%,respectively.This strategy can be used to design TPU with enhanced heat resistance without increasing the amount of diisocyanate.Lower usage of diisocyanate is apparently beneficial to people's health and the environment.