Research On The Effect Of Soft Segment On Properties Of Polyurethane Based On Polymerized MDI

At present,the study of polyurethane reinforced by continuous fiber is a focus in the field of polyurethane research.In this paper,high strength and modulus polyurethane were designed and prepared by using PMDI as the hard segment and different kinds of polyols as the soft segment.Research on the properties of polyurethane with different soft segment structure based on polymerized MDI(PMDI),we can have a grasp of properties of polyurethane influenced by soft segment structure.It is significant for guiding the development of low foaming two-component polyurethane with high strength and applying them to composites.PMDI has multiple rigid benzene rings and higher average functionality(about2.7).Polyurethane made from PMDI has excellent mechanical properties.Two-compon-ent polyurethanes were obtained with PMDI as the hard segment and different types of polyols as the soft segment.Firstly,polyurethanes were prepared by polyether polyol or polyester polyol and PMDI.It's tensile properties and flexural properties were tested.The effect of content,types and molecular weight of polyols on mechanical properties were studied.Then,the mixture of phthalic anhydride polyester polyol(PAPP)and polypropylene glycol(PPG)was selected as the soft segment.PMDI was selected as the hard segment.The content,functionality,and molecular weight of PAPP were changed.So two-component polyurethanes with high strength can be prepared.The effect of content,functionality and molecular weight of PAPP on performance of polyurethane were studied.Results indicate that polyether polyol was selected as the soft segment.As the proportion of polyether polyol(PPG400)decreases,the tensile strength of polyurethane firstly increases and then decreases and the flexural strength gradually increases.The mechanical strength and modulus of polyurethane with soft segment composed with PEG400 was little different than that of polyurethane with soft segment composed with PPG400.The mechanical strength and modulus of polyurethane with soft segment composed with PTMEG400 was best among them.When the molecular weight of PPG increases,the tensile strength and flexural strength gradually decrease.When the polyester polyol was selected as the soft segment,the tensile strength and flexural strength of polyurethane with soft segment composed with phthalic anhydride polyester polyol(PAPP400)was best.The mixture of phthalic anhydride polyester polyol(PAPP)and polypropylene glycol(PPG)was selected as the soft segment.When the content of PAPP increases,the tensile strength,flexural strength and impact strength firstly increase and then decrease.The glass transition temperature and deformation temperature gradually increase before being stable.The thermal decomposition temperature gradually increases.If the molecular weight PAPP is 400,the functionality of PAPP is 3 and the content of PAPP is 40%,the polyurethane has the best comprehensive mechanical properties.The tensile strength and tensile modulus were 66.4MPa and 2.90GPa respectively.The flexural strength and flexural modulus were 92.0MPa and 3.07GPa.The impact strength was 66.1kJ/m~2.The glass transition temperature was 72?.The epitaxial initial decomposition temperature was 267?.When the content of PAPP increases,the tensile strength,flexural strength and impact strength firstly increase and then decrease.If the molecular weight PAPP is 400,the functionality of PAPP is 3 and the content of PAPP is 40%,the polyurethane composite has good mechanical properties,the tensile strength was 465MPa.The flexural strength and flexural modulus were 552MPa and 19.3GPa,respectively.