Second, the difference between PP and PVC both from the appearance and feel can be clearly distinguished; PP feel harder and PVC is relatively soft, the best test is to use an open flame on the two materials burning, there is a black dusty is PVC and PP is not. From the smell can also be distinguished, PVC has a choking taste, while the PP is odorless
PP, PVC, PE difference
One, PVC (polyvinyl chloride)
1. Chemical and physical properties
Rigid PVC is one of the most widely used plastic materials. PVC material is a non-crystalline material. PVC materials in practice often add stabilizers, lubricants, auxiliary processing agents, color, impact resistance and other additives. PVC materials are non-flammable, high strength, resistant to weathering and have excellent geometric stability. PVC is highly resistant to oxidizing agents, sanitary pump reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid, concentrated nitric acid and is not suitable for contact with aromatic hydrocarbons, chlorinated hydrocarbons. The melting temperature of PVC is a very important process parameter when processing, and if this parameter is not correct, it will lead to problems with the decomposition of the material. The flow characteristics of PVC are quite poor and its process range is very narrow. Especially large molecular weight PVC materials are more difficult to process (such materials usually have to add lubricants to improve the flow characteristics), so it is usually small molecular weight PVC materials that are used. The shrinkage of PVC is quite low, typically 0.2 to 0.6%.2. Injection molding process conditions
Drying treatment: usually do not need drying treatment. Melt temperature: 185~205C Mold temperature: 20~50C Injection pressure: up to 1500 bar Holding pressure: up to 1000 bar Injection speed: In order to avoid degradation of the material, the injection speed should be quite high.Runners and gates: All conventional gates can be used. For smaller parts, it is best to use a pin-tip or dive gate; for thicker parts, it is best to use a fan gate. The minimum diameter of a pin-tip or submerged gate should be 1mm; the thickness of a fan gate should not be less than 1mm.
3. Typical Uses
Water supply piping, household plumbing, wall panels for houses, commercial machine housings, electronics packaging, medical equipment, food packaging, etc.
2. PP Polypropylene
1. Chemical and Physical Properties
2. PP is a semi-crystalline material. Metering pump it is harder than PE and has a higher melting point. Because the homopolymer type of PP is very brittle at temperatures above 0C, many commercial PP materials are irregular **** polymers with 1~4% ethylene added or higher ratio ethylene content of the pincer **** polymers. The *** polymer type of PP material has a lower heat distortion temperature (100C), low transparency, low gloss, low rigidity, but has a stronger impact strength.The strength of PP increases as the ethylene content increases. PP has a Vicat softening temperature of 150 C. Due to its high degree of crystallinity, this material has good surface stiffness and scratch resistance properties.
PP does not suffer from environmental stress cracking. Typically, PP is modified by the addition of glass fibers, metal additives, or thermoplastic rubber.The flow rate MFR of PP ranges from 1 to 40.PP materials with low MFR have better impact characteristics but lower ductile strength. For the same MFR, the *** polymer type is stronger than the homopolymer type. Due to crystallization, the shrinkage of PP is quite high, generally 1.8 to 2.5%. And the directional uniformity of shrinkage is much better than materials such as PE-HD. Adding 30% glass additive can reduce the shrinkage to 0.7%. Both homopolymer-type and *** polymer-type PP materials have excellent resistance to moisture absorption, acid and alkali corrosion, and solubility. However, it has no resistance to aromatic hydrocarbon (e.g., benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, and so on.2. Injection molding process conditions
Drying treatment: If stored properly no drying treatment is required. Melting temperature: 220~275C, be careful not to exceed 275C. Mold temperature: 40~80C, 50C is recommended. The degree of crystallization is mainly determined by the mold temperature. Injection pressure: can be as big as 1800bar. Injection speed: usually, using high speed injection can minimize the internal pressure. If defects appear on the surface of the product, then lower injection speeds at higher temperatures should be used. Runners and Gates:For cold runners, typical runner diameters range from 4 to 7mm.It is recommended to use injection ports and runners that are round through and through. All types of sprues can be used. Typical gate diameters range from 1 to 1.5mm, but gates as small as 0.7mm can be used. For edge gates, the minimum gate depth for test pumps should be half the wall thickness; the minimum gate width should be at least twice the wall thickness.PP materials are fully compatible with hot runner systems.3. Typical uses
1) Automotive industry (mainly PP with metal additives: fenders, vent pipes, fans, etc.), appliances (dishwasher door liners, dryer vent pipes, washing machine frames and covers, refrigerator door liners, etc.), consumer products (lawn and garden equipment such as lawn mowers and sprinklers, etc.).
2) Polyethylene is the most structurally simple polymer and the most widely used polymer material.
3) It is made by joining repeating -CH2- units. Polyethylene is produced by addition polymerization of ethylene (CH2=CH2).
4) The properties of polyethylene depend on how it is polymerized. High-density polyethylene (HDPE) is produced by Ziegler-Natta polymerization under moderate pressure (15-30 atm), catalyzed by organic compounds. Polyethylene molecules polymerized under these conditions are linear and have long molecular chains with molecular weights in the hundreds of thousands. If it is at high pressure (100-300MPa), high temperature (190-210 ° C), peroxide-catalyzed conditions of free radical polymerization, the production of low-density polyethylene (LDPE), it is branched structure.
5) Polymerization pressure size: high-pressure, medium-pressure, low-pressure;
6) Polymerization implementation methods: slurry method, solution method, gas-phase method;
7) Density size of the product: Self-priming pumps high-density, medium-density, low density, low-density, linear low-density;
8) Molecular weight of the product: low molecular weight, ordinary molecular weight, ultra-high molecular weight.
Three, PE polyethylene
Polyethylene odorless, non-toxic, feel like wax, has excellent low-temperature resistance (the lowest use of temperature up to -70 ~ -100 ° C), good chemical stability, resistant to most acids and alkalis (not resistant to the oxidizing nature of the acid), insoluble in general solvents at room temperature, water absorption is small, excellent electrical insulation; but polyethylene for the environmental stress ( However, polyethylene is very sensitive to environmental stress (chemical and mechanical effects) and has poor heat aging resistance.
The nature of polyethylene varies from species to species, depending mainly on the molecular structure and density.
Types of polyethylene
(1) LDPE: low-density polyethylene, high-pressure polyethylene
(2) LLDPE: linear low-density polyethylene
(3) MDPE: medium-density polyethylene, bimodal resin
(4) HDPE: high-density polyethylene, low-pressure polyethylene
(5) UHMWPE: ultra-high molecular weight polyethylene
(6) modified polyethylene: CPE, cross-linked polyethylene (PEX)
(7) Ethylene*** polymer: ethylene-propylene*** polymer (plastics), EVA, ethylene-butene*** polymer, ethylene-other olefins (eg, octene POE, cycloalkenes) **** polymer, ethylene-unsaturated ester **** polymers (EAA, EMAA, EEA, EMA, EMMA, EMAH)
Linear polyethylene with a molecular weight of 3,000,000-6,000,000 is known as ultra-high molecular weight polyethylene (UHMWPE). UHMWPE is so strong that it can be used to make bulletproof vests.
1.2 Physical Properties of Polyethylene
Polyethylene is a white waxy translucent material, flexible and tough, lighter than water, non-toxic, with superior dielectric properties. It is easy to burn and continue to burn after leaving fire. Water permeability is low, while the organic vapor permeability is large. The transparency of polyethylene decreases with the increase of crystallinity. Under a certain degree of crystallinity, the transparency improves with the increase of molecular weight. High-density polyethylene melting point range of 132-135oC, low-density polyethylene melting point is lower (112oC) and wide range.
It is insoluble in any known solvent at room temperature, and a small amount can be dissolved in solvents such as toluene, amyl acetate, tri-rate ethylene
1.3 Chemical Properties of Polyethylene
Polyethylene has excellent chemical stability, and is resistant to hydrochloric acid, hydrofluoric acid, phosphoric acid, formic acid, amines, sodium hydroxide, potassium hydroxide and other chemicals at room temperature, and nitric acid and sulfuric acid are very sensitive to polyethylene. Nitric acid and sulfuric acid have strong destructive effect on polyethylene. Polyethylene is easy to photo-oxidation, thermal oxidation, ozone decomposition, easy to degrade under the action of ultraviolet rays, carbon black has excellent light shielding effect on polyethylene. Crosslinking, chain breaking, formation of unsaturated groups and other reflections can occur after radiation.
1.4 Uses of various types of polyethylene products
High-pressure polyethylene: more than half of it is used for film products, followed by pipes, injection molding products, wire wrapping layer, etc.
Low and medium-pressure polyethylene: injection molding products and hollow products are mainly used.
Ultra-high-pressure polyethylene: due to the excellent comprehensive performance of ultra-high polymer polyethylene, it can be used as engineering plastics.
Polyethylene plastic relative molecular mass of more than 10 000, according to the different density is divided into high-density polyethylene, medium-density polyethylene and low-density polyethylene. Low-density polyethylene is softer, more high-pressure polymerization; high-density polyethylene is harder, more low-pressure polymerization. Low-density (high-pressure) polyethylene is often used in large quantities. Polyethylene is one of the most used plastics in the world today.
Polyethylene is waxy, wax-like smoothness, not coloring, low-density polyethylene transparent, while high-density polyethylene opaque, the biggest use is in agricultural greenhouses, food bags and so on. It is not afraid of water or oil, strong chemical resistance, and beautiful and practical.
Polyethylene (PE) is one of the most commonly used polymer materials in daily life, a large number of products used in the manufacture of plastic bags, plastic film, milk pails.