| Polycarbonate(PC)is an excellent engineering plastics due to its optical transparency,dimension stability,impact resistance,creep resistance,and wide temperature range etc.So,it is extensively used in commercial fields such as glass,automotive,electronic assembly industry,electrical industry,defense industry,medical treatment and health care,leisure and protective equipment etc.However,the optical and mechanical properties of PC strongly depended on its special molecular structure will changes gradually in the process of forming,storage,use or under the comprehensive effect of various factors.It will shorten the service life time of the PC products,even lost their value.In this paper the main research contents are as follows:(1)The samples were molded by injection molding machine and micro-injection molding machine respectively,and were characterized by scanning electron microscopy and mechanical performance testing.The results showed that there is big differences in the stress-strain curves between injection molded sample and micro-injection molded sample.The tensile stress-strain curve of the microinjection molding sample exhibited the orientation strengthening stage.This difference was confirmed by the cross-sectional morphology of the samples.The skin percentage of micro-injection molded sample is larger than injection molded sample.There is an obvious transition layer between the shear layer and core layer in micro-injection molding specimen.(2)By using ultraviolet aging test chamber with UVA-340 type UV fluorescent lamp,the UV aging test was carried out.Then the aged samples were subjected to tensile test,DSC analysis,NM-indentation,UV-VIS spectrum,Fourier infrared spectrum polarizing microscope analysis etc.It was found that the aged sample changed from colorless and transparent to light yellow,the color of the sample gradually increased with the increase of UV aging time.The yield strength of sample has not decreased after UV irradiation aging,but the plasticity of product was significantly reduced.It was found that the cracks formed on the surface of injection molding sample became more and more small and intensive with the increase of aging time after the tensile test,it showed that the strength of the surface of sample was greatly reduced after UV aging.The specimens molding by the two forming method showed similar changing law after same aging.However,due to the size factor and skin-core structure,the plasticity of micro-injection sample reduced more quickly.Compared with thermal-oxidative aging test,it was found that the changing color was caused by UV aging.(3)The thermal-oxidative aging test was carried out by using thermal-oxidative aging test chamber at three temperatures 60?,90? and 120?respectively for the two kinds of forming methods samples,then the change of samples was analyzed after aging.It was found that the temperature of the thermal-oxidative aging had great importance for the aging degree and aging speed of products,the aging speed was increased with the increase of aging temperature.After the thermal-oxidative aging,the yield strength was increased,the plasticity was reduced,the yield strength was increased greatly and the plasticity was decreased quickly while the aging temperature increased.With the increase of thermal-oxidative aging time,the yield strength was increased to a certain and limited extent,yield strength of the sample had a downtrend after eight days aging in 120 ?.The differences of structure and dimension between micro-injection molding samples and injection molding samples led to different thermal-oxidative aging resistance,what's more,thermal oxidative aging resistance of the micro-injection molding sample became stronger,it still had good plasticity after 12 days aging in 120?.There was multiple defect point sin cross-section of aging in injection molding sample,however,it was not found in the micro-injection sample. |
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