Preparation And Properties Of Low Foaming,High Strength And High Toughness Polyurethane Resin

Polyurethane resin has been applied in many fields due to its excellent performance.While because of its dis-satisfactory strength,stiffness,heat resistance and some other properties,as a resin matrix of glass fiber reinforced composite,its performance is far less than the requirements.Compared with foreign countries,the study of two-component polyurethane resin is late-starting point and low maturity,which limiting the development of polyurethane resin.Therefore,the high performance polyurethane resin which can be used in fiber reinforced composites is the hot spot of the present research.In order to obtain high strength,high toughness and less bubbles of polyurethane resin,toluene-2,4-diisocyanate?TDI?/polypropylene glycol?PPG?were uesed to synthesize prepolymer by prepolymer method to reduce the content of isocyanate.Polytetrahydrofuran ether diol?PTMG?and phthalic anhydride polyester polyol?PAPP?were used as chain extender to reduce the polyurethane reactivity and the curing product bubble rate while increasing the molecular chain of the polyurethane prepolymer to improve the toughness of the cured product.And TMP is a cross-linking agent,which can form a crosslinked three-dimensional network structure and stiffness to improve the strength of the cured product.The optimum conditions for the synthesis and storage of TDI/PPG polyurethane prepolymer were determined by di-nbutylamine method,and the change of viscosity was studied.Then study the static mechanical properties of the polyurethane resin systems after chain extension reaction by an electronic universal testing machine,study the curing reaction kinetics,structure characteristics and fracture morphology by the means of non-isothermal DSC,FT-IR and SEM,DMA is preferred to study heat resistance and observe the change regulation of Tg?glass-transition temperature?.The optimum reaction conditions for TDI/PPG polyurethane prepolymer is 80?for two hours.The viscosity of the polyurethane prepolymer will decrease when the content of-NCO increases in less storage time?in two weeks?or reacting at promoting temperature.The result of FT-IR shows that evident-NHCOO and-NCO characteristic absorption peaks have appeared while the characteristic absorption peak of-OH has disappeared,which means the polyurethane prepolymer with capping group of-NCO has been synthesized.The absence of the characteristic absorption peaks of-OH and-NCO proves that-NCO has completely assumed during the polyurethane prepolymer chain extension reaction.Compared with the PU castings of the linking reaction of TMP single system,the tensile and flexural strength of PU castings of PTMG/TMP,a mixed chain extension crosslinking system,decreased slightly,but the elongation at break larger increase.The results show that the polyurethane foams are less effective and have less influence on the mechanical properties,and the PU castings of the mixed system have better toughness.When the content of PTMG400 is 5%in the mixed chain crosslinking agent,the concentration of-NCO in the TDI/PPG400 prepolymer is24.50%and the R value is 1.01¹.05,the polyurethane prepolymer has the best comprehensive properties:92.1MPa⁹5.2MPa for tensile strength,113MPa¹16MPa for bending strength,3.51GPa³.54GPa for tensile modulus,4.97%⁴.98%for elongation at break,which is 47.5%higher than that of TMP single system,and 49.7kJ·m^-249.9kJ·m^-22 for the impact strength,improved by nearly 260%,which is characterized by rough surface,stripe and deep through the SEM.The characteristic temperature of polyurethane resin can be influenced by the content of-NCO.More-NCO lead to higher characteristic temperature,but excess PTMG chain extender will lower the temperature.Changes of R value hardly influence the temperature.Polyurethane casting of PTMG400/TMP hybrid chain extension cross-linking system reaches 89.0?⁹6.0?as inflection point temperature and116?¹18? as Tg.