Environmental Durability And Mechanism Of Polyurethane Adhesive

Polyurethane adhesive is one of the important part of polyurethane resin, which is developing strongly. It is also one of the eight compounded adhesives, which have excellent ability of cold resistance and thermal resistance and can be used abroad in shoemaking,architecture,auto car and packaging is recognized as one of the most potentially developing adhesives. But there are little study on the durability and mechanism of polyurethane adhesive at present.This test used the currency polyurethane as raw materials. The tensile shear strength of polyurethane adhesive after aged in environment was measured by Lap shear strength test, and the effect of temperature,time and mediums on adhesive durability were experimentally researched by tensile shear strength's residual rate. SEM observation and FT-IR analysis of the sample surfaces were carried out. The thermal stability of polyurethane adhesive was investigated by TGA and DTG, and the lifetime estimates was also given. The process of the preparation consists of : (1) The effect of acid,alkali and salt(different temperature and concentration) on polyurethane adhesive was studied. The results showed that the polyurethane adhesive's bonding strength decreased exponentially with the immersion time in distilled water,NaCl and H2SO4, and its bonding strength rapidly reduced at the early stage of immersion and changed hardly at the last stage of immersion with the increase of temperature, and which decreased linearly in NaOH until to be zero . (2) The effect of gaseous water on polyurethane adhesive was studied. The results showed that polyurethane adhesive's gaseous water resistance was of a sort, and adhesive's bonding strength ascended in both liquid water and gaseous water, but which ascended more rapidly in gaseous water. (3) Polyurethane adhesive's tensile shear strength residual rate decreased to be 70% under UV irritated, and its strength no longer changed, but waved at this level. Adhesive's bonding strength decreased persistently under UV irritation and water, and its surfaces changed largely at the last stage of ageing. (4) The kinetics on thermal degradation of polyurethane adhesive were studied. It is proved that there are three main decomposition stages, and the non-isothermal degradation was found to be first order reaction. The apparent activation energy increased with the increase of weight mass losses. In addition, the kinetic data indicates that polyurethane adhesive have excellent thermal stability, and the lifetime estimates indicated the 10 year lifetime temperature maximum of polyurethane in air to be 52℃.