Research On Polypropylene Modification Based On Ultrasonic Crystal Structure Control

Polypropylene,as one of the five most widely used plastics,has many outstanding advantages,such as low price,non-toxic products,insulation,easy to process and shape,which makes it popular in many fields.Although polypropylene has many advantages,it still has some defects,among which poor aging resistance is one of the more serious defects,which limits the application of polypropylene to outdoor materials.Therefore,the study of aging resistance modification of polypropylene has become a very important research focus.Polypropylene is a kind of polycrystalline polymer,in which the?and?crystals are of practical value.The crystalline structure influence the anti-aging performance,the crystal grain of?crystal is larger than that of?crystal,the light is not easy to pass through?crystal,the?crystal has better anti-aging performance than?crystal.In this paper,using the rare earth?nucleating agent as additive and polypropylene as the substrate,the ultrasonic vibration assisted regulation of the structure of polypropylene crystal modified by rare earth?nucleating agent was systematically studied in order to improve the anti-aging properties of polypropylene.Based on the research above,this thesis has finished the following works,and gains the research rusults as following:?1?The effect of synergistic effect of ultrasonic vibration and cooling temperature on the structure,mechanical properties and anti-aging properties of polypropylene crystal modified by rare earth?nucleating agent was studied.The results show that cooling temperature and ultrasonic vibration can improve the tensile strength and anti-aging properties of polypropylene by changing the crystallinity of polypropylene modified by rare earth?nucleating agent.With the increase of cooling temperature,the better the dispersion of?-nucleating agent in PP matrix is,and the more homogeneous the dispersion of?-nucleating agent in PP matrix after ultrasonic vibration is compared with that without ultrasonic vibration,thus affecting the nucleation process of polymer in the cooling process.At the same cooling temperature,the crystallinity and the relative content of?-crystal of PP modified by?nucleating agent after ultrasonic treatment were significantly higher than those without ultrasonic treatment,which showed that the tensile properties of PP modified by?nucleating agent after ultrasonic treatment were significantly higher.At the same time,ultrasonic treatment and cooling temperature have certain influence on the crystallization process of polypropylene.The best condition is that the ultrasonic treatment temperature is 70?,and the shortest semi crystallization time of polypropylene modified by rare earth?nucleating agent is 0.30 min,the fastest crystallization rate constant Z_c is 1.20,that is to say,applying ultrasonic vibration at a higher cooling temperature can accelerate the crystallization rate,so as to obtain a higher relative content of?crystal and a higher sum of crystallinity.At this time,after four cycles of aging test,the tensile strength of polypropylene modified by rare earth?nucleator reaches the maximum value of 34.81 MPa.?2?The effect of ultrasonic vibration distance on the structure,mechanical properties and anti-aging properties of polypropylene crystal modified by rare earth?nucleating agent was studied.The results show that when the nearest ultrasonic distance is 1 cm,the more evenly the?nucleator disperses in the polypropylene matrix,the higher the crystallinity of the modified polypropylene.Under this condition,the efficiency of nucleator and the crystallinity of the modified polypropylene are optimized,which shows that the tensile property of the polymer under this condition is the best.However,with the increase of ultrasonic distance,?nucleating agent particles adhere and accumulate in the polypropylene matrix,which is easy to form agglomerates.At this time,the total crystallinity and the relative content of?crystal of modified polypropylene also show a decreasing trend.In the study of non isothermal crystallization kinetics,the closest distance ultrasonic vibration has the best induction effect on the polypropylene?form.The shorter half crystallization time is t_1/2 0.10 min,the crystallization rate is relatively fast,and the crystallization rate constant Z_c is 1.20,resulting in a higher relative content and crystallinity of?crystal,showing the best anti-aging property.After 4cycles of xenon lamp aging test,the tensile strength of PP modified by rare earth?nucleator reached the maximum value of 27.95 MPa when the ultrasonic vibration distance was 1 cm.?3?The effects of ultrasonic vibration power on the crystal structure,mechanical properties and anti-aging properties of modified polypropylene were studied.The results show that the more ultrasonic vibration power is applied,the more uniform the dispersion of?nucleating agent in PP matrix is.When the ultrasonic vibration power is increased,the relative content of?crystal changes obviously,and the change range of crystallinity is relatively small,which shows that the ductility and toughness are improved,the tensile capacity is enhanced,and the tensile strength of polymer is improved.When the ultrasonic power is 300 W,the tensile strength of modified polypropylene is the strongest,which is 49.53 MPa.In the study of non isothermal crystallization kinetics,higher ultrasonic vibration power can obtain shorter semi crystallization time,t_1/2 is 0.31 min,and the crystallization rate constant Z_c is 1.21,so as to obtain higher?crystal relative content and summary crystallinity.At this time,the tensile strength of polypropylene modified by rare earth?nucleating agent after three cycles of xenon lamp aging test reaches the maximum value of 36.75 MPa.