Study On The Preparation, Structure And Performance Of Aging-resistant One-component Polyurethane Adhesive

The weak chemical bonds such as C-H,C-N and C-O in the molecular chain of polyurethane were sensitive to light,heat,oxygen,etc,and will be aged during storage and use,thus,the overall performance of PU adhesives will be reduced.In this paper,the modifiers with anti-photooxidation and thermal oxidation resistance were prepared by chemical method to improve the weather resistance of polyurethane adhesives.Firstly,TiO₂-TDI particles and TiO₂-TDI-2246 particles were prepared by using rutile nano titanium dioxide（TiO₂）,antioxidant 2246 and toluene 2,4-diisocyanate（TDI）as main raw materials.The structure of TiO₂,TiO₂-TDI and TiO₂-TDI-2246 particles was characterized by fourier transform infrared spectroscopy（FTIR）,thermogravimetric analysis（TGA）,X-ray photoelectron spectroscopy（XPS）,ultraviolet-visible diffuse reflection spectroscopy（UV-vis）.The results showed that TDI was successfully bonded on the surface of nano-TiO₂ particles,and TiO₂-TDI particles was successfully prepared.Then,TiO₂-TDI-2246 particles was prepared by further grafting with antioxidant 2246.Compared with TiO_2,TiO₂-TDI and TiO₂-TDI-2246particles exhibited better absorption capacity in visible light region.Then the PU adhesive was modified by adding TiO₂,TiO₂-TDI and TiO₂-TDI-2246particles respectively,and the adhesives named as PU+TiO₂,PU+TiO₂-TDI and PU+TiO₂-TDI-2246 were prepared.The morphology of cross-section,tensile shear strength and heat resistance of prepared adhesives were analyzed by scanning electron microscopy（SEM）,electronic universal material testing machine and thermogravimetric analysis（TGA）,respectively.The results showed that the dispersibility of TiO₂,TiO₂-TDI and TiO₂-TDI-2246 particles in the adhesive was TiO₂-TDI-2246>TiO₂-TDI>TiO₂,The tensile shear strength of pure polyurethane adhesive was 0.65 Mpa,the largest tensile shear strength of PU+TiO₂ and PU+TiO₂-TDI adhesives was achieved at 0.4%content of TiO₂ and TiO₂-TDI,and the tensile shear strength of PU+0.4%TiO₂ and PU+0.4%TiO₂-TDI adhesives was 0.81 Mpa and 1.11 Mpa,respectively.Compared with the pure polyurethane adhesive and PU+0.4%TiO₂ adhesive,the tensile shear strength of PU+0.4%TiO₂-TDI adhesive increased respectively of about 70.5%and 36.7%.The largest tensile shear strength of about 1.24 Mpa was found in the PU+TiO₂-TDI-2246 adhesive when the addition amount of TiO₂-TDI-2246 was 0.6%,compared with the pure polyurethane adhesive and PU+0.4%TiO₂ adhesive,the tensile shear strength of the PU+0.6%TiO₂-TDI-2246adhesive increased respectively of about 90.4%and 53.1%.In addition,the thermal stability of PU adhesive modified by TiO₂-TDI-2246 particles was improved.The artificial accelerated aging test of the adhesive PU,PU+TiO₂,PU+TiO₂-TDI and PU+TiO₂-TDI-2246 was carried out through a xenon lamp test chamber and an oven,The mechanical properties,surface morphology,carbonyl index and hardness were analyzed respectively by an electronic universal material testing machine,scanning electron microscope（SEM）,infrared（FTIR）and Shore hardness tester（SHORE-A）.The results show that the PU+TiO₂,PU+TiO₂-TDI and PU+TiO₂-TDI-2246 adhesives exhibit anti-photooxidative aging properties,under the same irradiation time,the surface cracks of PU+TiO₂,PU+TiO₂-TDI and PU+TiO₂-TDI-2246 adhesives were less than that of PU adhesive.The carbonyl index（CI）of PU adhesives increased almost linearly with the increase in irradiation time and reached at about 45 after 1000 h of irradiation time.However,the carbonyl index of the PU+Ti O₂,PU+TiO₂-TDI and PU+TiO₂-TDI-2246adhesives change slightly and reached at about 12 after 1000 h of irradiation time.The tensile shear strength of the PU+0.4%TiO₂-TDI-2246 adhesive was higher than that of pure PU adhesive,PU+0.4%TiO₂ and PU+0.4%TiO₂-TDI throughout the thermal aging process.After1800 h of aging time,the retention rate of tensile shear stress of PU+0.4%TiO₂-TDI-2246adhesive was about 85%,while the retention rate of tensile shear stress of the other adhesives was only about 65%.