Study On Rheological And Mechanical Properties Of Medical Polypropylene Recycled Materials

As a common polymer material,isotactic polypropylene has been widely used in the field of medical devices due to its advantages of non-toxicity,convenient molding and low cost.Polypropylene is a polycrystalline structural material that produces different crystal forms when the molecular chains are aligned and stacked in different processing conditions.When producing and processing medical polypropylene for injection needle products,in order to reduce the cost,a certain amount of isotactic polypropylene old material is added to the isotactic polypropylene new material,but according to the reflection of the enterprise and the user,too much is added.After the propylene old material,it is easy to cause the injection molded product to be brittle.In this paper,0%,25%,50%,75% and 100% old materials were prepared by rheometer and injection molding machine.The rheological properties of the product were tested by a rotary rheometer,the crystallization behavior of the product was measured by wide-angle X-ray diffraction,the thermal crystallization temperature and melting temperature of the product were measured by differential scanning calorimetry,and the spherulite size of the raw materials and the old material was observed by a polarizing microscope.And the mechanical properties of the product were tested using a versatile experiment.The intrinsic relationship between the addition of different old materials at temperatures of 190°C and 210°C and the changes in crystal structure and macroscopic mechanical properties at 190 °C and 230 °C was investigated.In order to further study the influence of different old materials on the structural changes of the microscopic molecular chain and the mechanical properties of the system from the molecular level,the molecular dynamics method was used to construct the old material content of 0%,20%,40%,60%.,80% and 100% of the six system cells,and the shear flow simulation and mechanical properties of the six systems were simulated.The microscopic molecular chain orientation,molecular chain bond length and bond angle of different systems before and after shearing were analyzed.The changes were finally analyzed for the mechanical properties of different systems.Rotary rheometer test shows that the old material and temperature will change the shear viscosity of the system.The shear viscosity of different systems will decrease with the increase of the old material content,while the temperature increase will reduce the viscosity of the system;wide-angle X-ray diffraction test indicates the addition The old material produces ? and ? polycrystalline structure inside the system,and the more the content of the old material,the more the ? crystal content,the more likely the product is to be brittle,the content is between 25% and 50%.The content of ? crystal is relatively stable;the increase of the content of old materials and the increase of temperature increase the crystallinity of isotactic polypropylene;the degree of orientation decreases with the increase of temperature and the proportion of old materials;the old materials and temperature will affect the pulling of isotactic polypropylene.The tensile strength and Young's modulus,the tensile strength is relatively stable at the old material content of 25% and 50%,and the Young's modulus does not change much when the old material is 25%.The mean square radius of gyration indicates that the molecular chains of different systems are in a state of random entanglement when they are not sheared.After undergoing shearing,the molecular chains of each system are oriented to a certain extent;the system is subject to After the shearing action,the C-H and C-C bond lengths of the molecular chain will be stretched,and the more the old material content,the greater the probability that the bond length will be stretched,but the overall structure of the molecular chain is not sheared and destroyed;The bulk modulus and shear modulus of the system decrease with the increase of the old materials.The variation of Young's modulus with the old materials is consistent with the experimental results,and the numerical range is also consistent with the real material structure of polypropylene.