PP The production process of polypropylene copolymer can be divided into two kinds according to the different catalysts. One is metallocene catalyst, the other is an improved Ziegler-Natta efficient catalyst. The metallocene catalyst has only one active center compared with the Ziegler-Natta catalyst, while the Ziegler-Natta catalyst has multiple active sites. Metallocene catalysts can precisely control molecular weight and its distribution, the content of monomer and its distribution and crystal structure on polymer chains. The application of Ziegler-Natta catalyst in PP copolymerization is characterized by simple production process, low energy consumption, high molecular nucleation and polymer performance. Crosslinking modification The crosslinking modification of polypropylene is an effective way to improve the thermal deformation temperature of polypropylene, and also improve the mechanical properties of polypropylene. Crosslinking modification mainly includes radiation crosslinking and chemical crosslinking. Radiation crosslinking is a free radical and cross-linking reaction of the molecular chain of polypropylene under the action of high energy rays. Chemical crosslinking is generally used to add peroxide to PP as an initiator, and the crosslinking agent is added to the crosslinking reaction. During the crosslinking modification of polypropylene, the degradation and crosslinking reaction exist simultaneously. The crosslinking efficiency is relatively low when using radiation crosslinking, while chemical crosslinking is generally used to promote crosslinking reaction by adding auxiliary crosslinking system with Blending modification is a simple and effective modification method. It can be blended with other plastics, rubber?or?thermoplastic elastomers with PP to prepare polymer alloys with both properties of these polymers. The blending modification of polypropylene can improve the low temperature impact resistance, transparency, coloring and antistatic properties of the polymer. Because the blending modification has the advantages of simple operation, short production cycle and suitable for mass production, the development of blending is very rapid. Commonly used in polypropylene modified polymer polyethylene (PE) and polyamide (PA) and ethylene propylene rubber (EPR), three EPDM (EPDM), butadiene rubber (ER) and styrene butadiene styrene block copolymer (SBS), ethylene vinyl acetate copolymer (EVA) etc.. EPDM, SBS and EVA elastomer blended with PP, elastic particles in the material can absorb some of the impact energy, and as a stress concentration to induce agent and inhibition of crack growth, the PP changes from brittle fracture to ductile fracture, the impact strength is greatly improved, effectively improve the toughness of PP. The blending of PA, ABS and other rigid polymers with PP can ensure the strength and rigidity of the material at the same time. However, because these rigid polymers are polar polymers, the compatibility of these polymers with PP is poor, and the proper compatibilization system must be added to the modification. TPV Drying: dry treatment is not required if the storage is appropriate. Melting temperature: the melting point of PP is 160-175 C, the decomposition temperature is 350 C, but the temperature setting can not exceed 275 C during the injection processing. The temperature of the melting section is best at 240. Mold temperature: the mold temperature is 50-90 degrees C, for the high requirement of the size of the high mold temperature, the core temperature is lower than 5 degrees centigrade. Injection pressure: high injection pressure (1500-1800bar) and pressure holding pressure (about 80% of the injection pressure). At about 95% of the full stroke, the reinsurance pressure is used, and the longer holding time is used. Injection speed: in order to reduce internal stress and deformation, high speed injection should be chosen, but some grades of PP and die are not applicable (bubbles and air lines). Low velocity injection and higher mold temperature should be used if the surface of the pattern has a bright and dark fringe that is spread by the gate. The runner and gate runner diameter: 4-7mm, needle gate length 1-1.5mm, diameter up to 0.7mm. The shorter the edge of the gate, the shorter the better, it is about 0.7mm, the depth is half of the wall thickness, the width is two times of the wall thickness, and it increases with the length of the melt flow in the die cavity. The mold must have good exhaust performance, and the exhaust port is 0.025mm-0.038mm deep and 1.5mm thick. To avoid shrinkage mark, we must use large and round nozzle and circular channel, and the thickness of reinforcing rib is small (for example, 50-60% of wall thickness). The products made by homopolymer PP are not more than 3mm in thickness, otherwise there will be bubbles (the thick wall products can only be PP). Back pressure of melt adhesive: the back pressure of 5bar glue can be used, and the back pressure of the color powder can be properly adjusted. Post-processing of products: in order to prevent the shrinkage and deformation of the post crystallized products, the products are usually soaked in hot water. application Household Electric Appliances HDPE copolymerized monomer. This change is generally measured by the density, and the density is linearly related to the crystallization rate. The United States is generally classified according to ASTM D1248, the density of HDPE is above 0.940g/CC, and the density range of medium density polyethylene (MDPE) is 0.926 to 0.940g/CC. Other classifications are sometimes classified as MDPE in HDPE?or?LLDPE. The homopolymer has the highest density, the maximum rigidity, the good anti permeability and the highest melting point, but generally has the very poor resistance to environmental stress cracking (ESCR). ESCR is the ability of PE to resist cracking caused by mechanical?or?chemical stress. Higher density generally improves mechanical strength, such as tensile strength, stiffness and hardness, thermal properties such as softening point temperature and hot deformation temperature, and permeability resistance, such as air permeability?or?water vapor permeability. Low density improved the impact strength and ESCR. The polymer density is mainly influenced by the addition of the copolymerized monomers, but less to the molecular weight. The percentage of high molecular weight decreases the density slightly. For example, the homopolymer has a different density in a wider range of molecular weight. Production process Higher molecular weight leads to a higher viscosity of the polymer, but the viscosity is also related to the temperature and shear rate used in the test. The molecular weight of the material is characterized by rheological?or?molecular weight measurements. The molecular weight range of HDPE is generally 40000~300000, and the weight average molecular weight is roughly corresponding to the melting index range, that is, from 100 to 0.029g/10min (230 2.16kg). In general, higher Mw (lower melting index MI) enhanced melt strength, better toughness and ESCR, but higher Mw made processing. The process is more difficult?or?requires higher pressure?or?temperature. Molecular weight distribution (MWD): the WD of PE varies from narrow to wide according to the catalyst and process used. The most commonly used MWD measurement index is the unevenness index (HI), which is equal to the weight average molecular weight (Mw) divided by a number average molecular weight (Mn). The index range of all HDPE grades is 4 - 30. Narrow MWD provides low warping and high impact in the molding process. The medium to wide MWD provides the machinability for most of the extrusion processes. Wide MWD can also improve melt strength and creep resistance. Additive