Synthesis Of Polylactic Acid-based Thermoplastic Polyurethane And Study On Its Damping Properties

Elastomer materials have unique viscoelasticity,excellent damping,sound absorption,vibration suppression and noise reduction performance,and are widely used in defense equipment,precision instruments and equipment,and other fields.Traditional rubber damping materials,such as nitrile rubber(NBR),styrene-butadiene rubber(SBR),etc.,because of their low glass transition temperature,poor damping performance under working conditions and small controllable range,and synthetic rubber relies on petrochemical resources and cannot be recycled utilization,has been unable to meet the performance requirements of damping materials and products.Polyurethane elastomer has a polar macromolecular chain,strong designability of molecular structure,adjustable damping performance and a large control range,and has become the research focus of the new generation of damping materials.Thermoplastic polyurethane elastomer(TPU)also has the advantages of being reused many times and simple in processing technology.Facing the urgent demand for wide temperature range and high damping performance elastomer materials for national defense equipment,according to the group contribution theory of polymer materials,modified polylactic acid(PLA)polyols containing plenty of pendant methyl groups are used as soft segments for the synthesis of three types of polylactic acid based thermoplastic polyurethane(PLA-TPU)by prepolymer method.Compared with ordinary TPU,PLA-TPU has a high glass transition temperature and excellent damping performance which has a good application prospect in the field of high-performance damping materials and products.The main conclusions are as follows:(1)With hexamethylene diisocyanate(HDI)and 1,4-butanediol(BDO)as the hard segment and modified polylactic acid polyols with different number average molecular weights as the soft segment,HDI-type PLA-TPU was synthesized by the prepolymer method.The research results show that:the number of HDI-type PLA-TPU.The average molecular weight(Mn)is above 37,000,and the molecular weight distribution coefficient D is about 1.4;with the average hard segment length decreases(maintain modified polylactic acid polyol Mn=1000),or the molecular weight of the soft segment decreases(maintain the molar ratio of polyol,isocyanate,and chain extender at 1:2:1),broaden the damping temperature range(?T),loss factor peak(Tan ?max)and 0-60? loss The peak area(S0-60?)increases,showing good damping performance.The tensile strength of the material reaches 12 MPa,and the elongation at break is greater than 500%,which meets the requirements for mechanical properties of damping parts.In comparison,PLA3K-12 has the best damping performance,with ?T,Tan ?max,and S0-60? reaching 28.5?,0.65,and 19.3,respectively,showing good mechanical properties.This type of material can realize the regulation of damping performance and mechanical properties by changing the average hard segment length and soft segment molecular weight.The repeated processing performance of the PLA1K-34 sample was studied.The retention rates of tensile strength after three repeated processing were 97.5%,85.2%,and 68.7%respectively;the damping performance was improved.After the third repeated processing,the Tan ?max was 0.47,?T reached 20.5?,and S0-60? increased to 13.0,which increased by 38.2%,103%,and 17.1%respectively;indicating that the material has the characteristics of repeated processing and utilization.(2)In order to further improve the damping performance and mechanical strength of the material,diphenylmethane-4,4'-diisocyanate(MDI)and BDO are used as hard segments,and modified polylactic acid polyols with different number average molecular weights are used as soft segments.MDI-type PLATPU was synthesized by the prepolymer method.The research results show that the Mn of MDI-type PLA-TPU is more than 11,000,and the molecular weight distribution coefficient D is about 1.90;with the average hard segment length decreases(maintain modified polylactic acid polyol Mn=2000),or the molecular weight of the soft segment decreases(maintain the hard segment content at 32%),?T widens,Tan ?max and S0-60? increase,showing excellent damping performance.The tensile strength of the material reaches 28.3 MPa,and the elongation at break is greater than 300%,which meets the requirements for mechanical properties of damping parts.In comparison,PLA2K-23 has the best damping performance,with ?T,Tan ?max,and S0-60? reaching 64.6?,1.24,and 30.6,respectively,showing good mechanical properties.This type of material can realize the regulation of damping performance and mechanical properties by changing the average hard segment length and soft segment molecular weight.The repeated processing performance of the PLA2K-32 sample was studied.The retention rates of tensile strength after three repeated processing were 99.5%,94.1%,and 90.4%respectively;the damping performance was improved.After the third repeated processing,the Tan ?max was 0.88,?T reached 38.1?,SO-60? increased to 26.7,which increased by 7.3%,38.1%,and 14.1%respectively;indicating that the material has the characteristics of repeated processing and utilization.(3)In order to broaden the damping temperature range of the material,the modified polylactic acid polyol and polycaprolactone polyol(PCL)are used as the mixed soft segment,and MDI and BDO are still used as the hard segment.The mixed soft segment is synthesized by the prepolymer method.The research results show that the Mn of the mixed soft-segment PLA-TPU is more than 20,000,and the molecular weight distribution coefficient D is about 1.5;with the increase of the PCL ratio,the damping performance is reduced,?T,Tan?max and S0-60? decreased by 15.1%,24.4%,and 20.9%respectively;Tg decreased from 30.1? to 12.6?,and the elongation at break increased from 418%to 1275%(increase by 205%).The tensile strength is basically unchanged;this type of material can adjust the PLA-TPU elasticity and damping working area by adjusting the ratio of PCL,and expand the use range of the material.