| With the rapid development of the green tire industry and the issuance of laws and regulations limiting tire fuel consumption,the study and exploit of low roll resistance tire materials is becoming more and more important.Hydroxyl terminated polybutadiene polyurethane elastomer(noted as HTPB-PU)has many excellent properties such as low rolling resistance,great wear resistance,solvent resistance and so on,which lays a good foundation for the next generation of tire materials.Nowadays,HTPB-PU is mainly polymerized based on hydroxyl terminated polybutadiene synthesized by free radical polymerization(noted as FHTPB)with a wide molecular weight distribution and a functionality over 2.In this article,hydroxyl-terminated polybutadiene synthesized by anionic polymerization(noted as AHTPB)with isometric chain structure was achieved as soft segment of polyurethane,and then HTPB-PU was polymerized through the reaction among AHTPB,isocyanate and chain extender.HTPB-PU was co-vulcanized with natural rubber to explore the possibility of applying polyurethane to retreaded tire treads.In the first part(Chapter 3)of this paper,AHTPB with controllable molecular weight,narrow molecular weight distribution and functionality close to 2 was prepared through anionic polymerization initiated by lithium naphthalene initiator.The pseudo-gel phenomenon was analyzed as the O-Li+active centers combining with each other,and the combining center with the polybutadiene main chain formed a metal carbonyl coordination bond which sharply increased the system viscosity.The experimental method of adding sodium alkoxide and exchanging the end-capping agent to dimethyl ethylene oxide and adjusting the polarity of the polymerization can't change the state of pseudo-gel the same as improving the functionality.When lowering the monomer concentration to less than 2%won't occur the phenomenon of pseudo-gel.The AHTPB with functionality about 1.95,controllable molecular weight and structure content of 1,2 about 87%-90%was synthesized.In the second part(Chapter 4)of this paper,the effects of hard segment content,post-curing time,chain extender ratio,and soft segment structure on polyurethane properties was analyzed.When the hard segment content of the HTPB-PU increased from 20%to 30%,the Tg increased from-80? to-65?,the tensile strength increased from 4.0 MPa to 6.1MPa,and the elongation at break reduced from 430%to 310%,the average size of phase separation decreased from 109 nm to 91 nm.The tensile strength increases by 170%and the elongation decreases by 55%after increasing the curing time from one week to four weeks.After curing four weeks,the mechanical properties of the polyurethane turned to be stable.When the ratio of BDO:TMP in the chain extender changed from 95:5 to 75:25,the tensile strength of the polyurethane elastomer was increased 5%,and the elongation at break decreased 10%.The tensile strength of AHTPB-PU and FHTPB-PU were 6.8 MPa and 4.1 MPa,and the elongation at break were 480%and 420%.However,the loss factor at 60?of AHTPB-PU turned to be higher than FHTPB-PU.In the third part(Chapter 5)of this paper,the peel strength between HTPB-PU and natural rubber was studied.Natural rubber with the lower pre-vulcanization degree has higher peel strength with HTPB-PU.The peel strength between polyurethane and nature rubber decreased as the hard segment content of polyurethane increased when the polyurethane got fully post-curing.As the hard segment content increased from 20%to 30%,the peel strength decreased from 5.18 KN/m to 4.50 KN/m.As a comparison,the peel strength between millable polyurethane and nature rubber was 0.54 KN/m,which was one tenth of the samples that we prepared.As a result,it makes the refurbishment of used tires and reducing the environmental pollution become possible. |
PDF Full Text Request