| The process parameters have a direct impact on the internal morphology of the injection molded parts and their light transmission properties and mechanical properties.The influence of the process parameters on the crystalline morphology of the injection molded parts and the analysis of the changes in light transmission properties and mechanical properties are conducive to improving the product performance.In this paper,polypropylene(PP)was used as the research material,and the parts were molded by injection molding machine.Then the crystalline form of the parts was measured by XRD,and the light transmission performance and mechanics of the haze transmittance tester and stress tester were tested.Performance,in order to study the different parts of the injection pressure and packing pressure crystalline morphology,light transmission properties and mechanical properties of the changes and their internal relations.The study of the crystal morphology of the product shows that the injection pressure has a great influence on the crystallinity,grain size and orientation degree,especially on the crystallinity,and the crystallinity is not monotonous as the injection pressure increases.Instead,it showed a trend of rising first and then falling,and the range of crystallinity was 36.86% and 50.92%.According to the data obtained from the test,the injection pressure that produces the maximum crystallinity is between 80 MPa and 100 MPa.The change of holding pressure has a certain influence on the crystal morphology but it is not significant.This may be due to the fact that the position we measured is farther away from the gate,and the melt flow caused by the pressureretaining action of the holding pressure can only be poured.Near the mouth,the effect of holding pressure on crystallinity,grain size,and orientation degree was not significant,and there was no obvious trend of change.The analysis of the crystal morphology at different radial positions of the same part shows that the crystallinity,grain size,and orientation degree gradually decrease as the gate distance increases.The study of the mechanical properties and light transmission properties of the parts shows that the mechanical properties are mainly affected by the degree of crystallinity and the molecular orientation,and the tensile strength and elastic modulus show a tendency of rising first and then decreasing with the increase of the injection pressure,and the change of crystallinity.The trend is similar,but the elongation at break gradually decreases with the increase of the injection pressure.The filling flow marks and orientation degree caused by the increase of injection pressure have a great influence on the light transmittance,resulting in the light transmittance of the parts gradually decreasing with the increase of the injection pressure,and the change of haze is similar to the change of crystallinity.The haze is mainly affected by the degree of crystallinity.In addition,the increase of the melt flow rate caused by the increase of the injection pressure will lead to an increase in the birefringence of the part,which is in line with the change tendency of the grain orientation.The pressure holding pressure has little effect on the transmittance and haze,and the birefringence will gradually increase with the increase of the holding pressure,mainly due to the larger melt pressure caused by the packing pressure during the packing process.The flow causes the orientation of the molecular chains leading to an increase in birefringence.The inhomogeneity of light transmission performance at various points of the article shows that,due to the change in the crystalline morphology,as the distance from the gate increases,the combined effect of the progressively lower crystallinity,grain size,and degree of orientation leads to light transmission.As the rate increases,the haze and birefringence decrease,and the transmittance,haze and birefringence also affect each other. |
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