[Science stickers] Differences and characteristics of PVC, CPVC, UPVC, PP and FRP

PP (polypropylene)

PP plastic chemical name: polypropylene, English name: olypropylene (PP for short), specific gravity: 0.9-0.91 g/cm3, molding shrinkage: 1.0-2.5%, molding temperature: 160-220℃.
Features: non-toxic, odorless, low density, strength, stiffness, hardness, heat resistance are better than low-pressure polyethylene, can be used at about 100 degrees, has good electrical properties and high-frequency insulation not affected by humidity, but low temperature It becomes brittle with time, is not wear-resistant, and is easy to age. Suitable for making general mechanical parts, corrosion-resistant parts and insulating parts. Common acid and alkali organic solvents have little effect on him and can be used for food utensils.
Molding characteristics:
1. Crystalline material, low hygroscopicity, easy to melt fracture, and easy to decompose in long-term contact with hot metal.
2. The fluidity is good, but the shrinkage range and shrinkage value are large, and shrinkage holes, dents and deformation are easy to occur.
3. The cooling speed is fast, the pouring system and the cooling system should slowly dissipate heat, and pay attention to controlling the molding temperature. The material temperature is easy to be oriented when the temperature is low and high pressure. The mold temperature is below 50 degrees, the plastic part is not smooth, and it is easy to produce poor welding and flow marks. It is prone to warpage and deformation above the temperature.
4. The plastic wall thickness must be uniform to avoid lack of glue and sharp corners to prevent stress concentration.

PVC (Polyvinyl Chloride)

Basic characteristics: It is one of the largest plastic products in the world. It is cheap and widely used. The polyvinyl chloride resin is white or light yellow powder.
Different additives can be added according to different purposes, and PVC plastics can present different physical and mechanical properties. Adding an appropriate amount of plasticizer to the polyvinyl chloride resin can be made into a variety of hard, soft and transparent products.
Rigid PVC has good tensile, flexural, compressive and impact resistance, and can be used as a structural material alone. The softness, elongation at break, and cold resistance of soft PVC will increase, but the brittleness, hardness, and tensile strength will decrease.
The density of pure polyvinyl chloride is 1.4g/cm3, and the density of polyvinyl chloride plastic parts added with plasticizers and fillers is generally 1.15-2.00g/cm3.
Polyvinyl chloride has good electrical insulation properties, can be used as low-frequency insulation material, and its chemical stability is also good. Due to the poor thermal stability of polyvinyl chloride, long-term heating will cause decomposition, release HCL gas, and make polyvinyl chloride discolor, so its application range is narrow, and the use temperature is generally between -15 and 55 degrees.
Main application: Polyvinyl chloride is synthesized from acetylene gas and hydrogen chloride to synthesize vinyl chloride and then polymerized. It has high mechanical strength and good corrosion resistance. Due to its high chemical stability, it can be used to make anti-corrosion pipelines, pipe fittings, oil pipelines, centrifugal pumps and blowers, etc. Polyvinyl chloride rigid boards are widely used in the chemical industry to make the lining of their respective storage tanks, corrugated boards of buildings, door and window structures, wall decorations and other construction materials. Due to its excellent electrical insulation performance, it can be used to manufacture plugs, sockets, switches and cables in the electrical and electronic industries. In daily life, PVC is used to make sandals, toys and artificial leather. When the plasticizer is added in an amount of 30% to 40%, soft polyvinyl chloride is produced, which has high elongation, soft products, good corrosion resistance and electrical insulation, and is often made into thin films. Industrial packaging, agricultural seedlings and daily raincoats, insulating layers, etc.
The difference between PVC and UPVC is that UPVC is unplasticized and its strength is relatively high.

CPVC (Chlorinated Polyvinyl Chloride)

Chlorinated polyvinyl chloride (CPVC) is made by chlorination modification of polyvinyl chloride (PVC) resin. It is a new type of engineering plastic. The product is white or light yellow odorless, odorless, non-toxic loose particles or powder. After the PVC resin is chlorinated, the irregularity of molecular bonds increases, the polarity increases, the solubility of the resin increases, and the chemical stability increases, thereby improving the heat resistance of the material, acid, alkali, salt, oxidant, etc. corrosion. The mechanical properties of the numerical heat distortion temperature are improved, the chlorine content is increased from 56.7% to 63-69%, the Vicat softening temperature is increased from 72-82 ℃ (increased to 90-125 ℃), and the maximum operating temperature can reach 110 ℃. The long-term use temperature is 95 ℃.

PVDF polyvinylidene fluoride

PVDF (Polyvinylidene fluoride) refers to polyvinylidene fluoride, mainly refers to the homopolymer of vinylidene fluoride or the copolymer of vinylidene fluoride and other small amounts of fluorine-containing vinyl monomers. It has the characteristics of both fluorine resin and general resin , In addition to good chemical resistance, high temperature resistance, oxidation resistance, weather resistance, and radiation resistance, it also has special properties such as piezoelectricity, dielectric properties, and thermoelectric properties. It is the production name of fluorine-containing plastics. The second largest product has a global annual production capacity of more than 53,000 tons.
PVDF is a PVDF fusible fluorocarbon resin for coatings made by homopolymerization of vinylidene fluoride (VDF) with a purity of ≥99.99%. The fluorocarbon paint made of 70% PVDF resin is sprayed or rolled, and the paint film is baked and has unparalleled super weather resistance and processing performance. It fully complies with the American building materials standard AAMA2605 and the People's Republic of China industry standard HG/T3793-2005. PVDF not only has strong abrasion resistance and impact resistance, but also has high fading resistance and UV resistance in extremely harsh and harsh environments.
Product features:
1. Fluorinated resin (commonly known as thermoplastic Teflon) that can be injected and extruded.
2. Excellent chemical resistance.
3. Wear resistance, high mechanical strength and toughness.
4. Weather resistance, anti-ultraviolet and nuclear rays.
5. Good heat resistance and high dielectric strength.
Uses: chemical resistant parts, wires and cables, etc.

FRP (Fiber Reinforced Composite Plastic)

FRP (Fiber Reinforced Plastics) is fiber reinforced plastic, generally refers to the use of glass fiber reinforced unsaturated polyester, epoxy resin and phenolic resin matrix, commonly known as glass fiber reinforced plastic.
FRP has the following characteristics:

1. Lightweight and high strength
The relative density is between 1.5 and 2.0, which is only 1/4 to 1/5 of that of carbon steel, but the tensile strength is close to or even higher than that of carbon steel, and the specific strength is comparable to that of high-grade alloy steel. Therefore, it has excellent results in aviation, rockets, space vehicles, high-pressure vessels, and other products that need to reduce their own weight. The tensile, flexural and compressive strengths of some epoxy FRP can reach more than 400Mpa. Note: The specific strength is the strength divided by the density.
2. Good corrosion resistance
FRP is a good corrosion-resistant material, and has good resistance to atmosphere, water and general concentrations of acids, alkalis, salts, and a variety of oils and solvents. It has been applied to all aspects of chemical corrosion protection and is replacing carbon steel, stainless steel, wood, non-ferrous metals, etc.
3. Good electrical performance
FRP is an excellent insulating material used to make insulators. It can still protect good dielectric properties under high frequency. It has good microwave permeability and has been widely used in radomes.
4. Good thermal performance
FRP has low thermal conductivity, 1.25~1.67kJ/(m•h•K) at room temperature, only 1/100~1/1000 of metal, and is an excellent thermal insulation material. It is an ideal thermal protection and ablation resistant material in the instantaneous ultra-high temperature situation, and can protect the spacecraft from the erosion of high-speed airflow above 2000 ℃.
5. Good designability
① A variety of structural products can be flexibly designed according to needs to meet the requirements of use, and the product can have a good integrity.
②Materials can be fully selected to meet the performance of the product. For example, it can be designed to be corrosion-resistant, resistant to instantaneous high temperature, the product has particularly high strength in a certain direction, and has good dielectric properties, and so on.
6. Excellent craftsmanship
①The molding process can be flexibly selected according to the shape, technical requirements, use and quantity of the product.
②The process is simple, it can be formed at one time, and the economic effect is outstanding, especially for products with complex shapes and small quantities that are not easy to form, and its process superiority is more prominent.
One FRP cannot be required to meet all requirements. FRP is not a panacea. FRP also has the following shortcomings.
1. Low modulus of elasticity
The elastic modulus of FRP is twice larger than that of wood, but 10 times smaller than that of steel (E=2.1×106). Therefore, the product structure often feels insufficient rigidity and is easy to deform.
It can be made into a thin shell structure, a sandwich structure, or made up of high modulus fibers or reinforcement ribs.
2. Poor long-term temperature resistance
Generally, FRP cannot be used for a long time at high temperature. The strength of general-purpose polyester FRP decreases significantly above 50°C, and generally only used below 100°C; general-purpose epoxy FRP has a significant decrease in strength above 60°C. But you can choose high temperature resistant resin, so that the long-term working temperature is 200~300℃ is possible.
3. Aging phenomenon
Aging phenomenon is a common defect of plastics, and FRP is no exception. Under the action of ultraviolet rays, wind, rain, snow, chemical media, and mechanical stress, it is easy to cause performance degradation.

4. Low interlayer shear strength
The interlaminar shear strength is borne by the resin, so it is very low. The bonding force between layers can be improved by selecting processes and using coupling agents. The most important thing is to avoid shearing between layers as much as possible during product design.

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