Differences and Characteristics of PVC, CPVC, UPVC, PP and FRP


PP (polypropylene) PP plastic chemical name: polypropyl […]

PP (polypropylene)

PP plastic chemical name: polypropylene, English name: olypropylene (abbreviation PP), specific gravity: 0.9-0.91 g / cubic centimeter, mold shrinkage: 1.0-2.5%, molding temperature: 160-220 °C.
Features: Non-toxic, odorless, low density, strength and stiffness, hardness and heat resistance are all better than low-pressure polyethylene, can be used at about 100 degrees, with good electrical properties and high frequency insulation not affected by humidity, but at low temperatures. Brittle, not wearable, easy to aging. Suitable for making general mechanical parts, corrosion-resistant parts and insulating parts. The common acid and alkali organic solvents have little effect on him and can be used for food utensils.
Molding characteristics:
1. Crystalline material, low moisture absorption, easy to melt rupture, long-term contact with hot metal is easy to decompose.
2. The fluidity is good, but the shrinkage range and the shrinkage value are large, and the shrinkage cavity, dent and deformation are easy to occur.
3. Cooling speed, pouring system and cooling system should be slowly cooling, and pay attention to control the molding temperature, material temperature is easy to orientate at low temperature and high pressure, mold temperature is less than 50 degrees, plastic parts are not smooth, easy to produce poor welding, flow marks, 90 Above the degree of warping deformation.
4. The wall thickness of the plastic 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 world's largest production of plastic products, cheap, widely used, polyvinyl chloride resin is white or light yellow powder. Different additives can be added according to different purposes. PVC plastics can exhibit different physical properties and mechanical properties. Adding a proper amount of plasticizer to polyvinyl chloride resin can make a variety of hard, soft and transparent products. Hard PVC has better tensile, flexural, compressive and impact resistance and can be used alone as a structural material. The soft PVC, the elongation at break, and the cold resistance increase, but the brittleness, hardness, and tensile strength decrease. The density of pure polyvinyl chloride is 1.4 g/cm3, and the density of polyvinyl chloride plastic parts to which plasticizers and fillers are added is generally 1.15-2.00 g/cm3.
PVC 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 PVC, prolonged heating will lead to decomposition, release HCL gas, so that polyvinyl chloride color, so its application is narrow, the use of temperature is generally between -15 to 55 degrees.
Main application: PVC is synthesized from acetylene gas and hydrogen chloride and then polymerized. It has high mechanical strength and good corrosion resistance. Because of its high chemical stability, it can be used to make anti-corrosion pipes, pipe fittings, oil pipes, centrifugal pumps and blowers. Polyvinyl chloride hard plates are widely used in the chemical industry to make linings for their own storage tanks, corrugated boards for buildings, door and window structures, wall decorations and other construction materials. Due to its excellent electrical insulation properties, it can be used in electrical and electronic industries for the manufacture of plugs, sockets, switches and cables. In daily life, polyvinyl chloride is used to make sandals, toys and artificial leather. When the plasticizer is added in an amount of 30% to 40%, a soft polyvinyl chloride is obtained, which has a high elongation rate, a soft product, good corrosion resistance and electrical insulation, and is often used as a thin film. Industrial packaging, agricultural education and daily raincoats, insulation 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 a new type of engineering plastics that is obtained by chlorinating modified polyvinyl chloride (PVC) resins. This product is white or light yellow, odorless, odorless, non-toxic loose particles or powder. After the chlorination of PVC resin, the irregularity of the molecular bond increases, the polarity increases, the solubility of the resin increases, the chemical stability increases, thereby improving the heat resistance of the material, acid, alkali, salt, oxidant, etc. corrosion. Improve the mechanical properties of the value of the heat distortion temperature, the chlorine content from 56.7% to 63-69%, Vicat softening temperature from 72-82 °C, (to 90-125 °C), the maximum use temperature up to 110 °C, Long-term use temperature is 95 °C.


FRP (Fiber Reinforced Plastics)
FRP (Fiber Reinforced Plastics) is a fiber reinforced plastic, generally refers to the use of glass fiber reinforced unsaturated polyester, epoxy resin and phenolic resin matrix, commonly known as glass steel.
FRP has the following features:
1. Lightweight and strong
The relative density is between 1.5 and 2.0, only 1/4 to 1/5 of carbon steel, but the tensile strength is close to or even exceeds that of carbon steel, and the specific strength can be compared with that of high-grade alloy steel. Therefore, it has excellent results in aviation, rockets, spacecraft, high-pressure vessels, and other applications where it is necessary to reduce its own weight. Some epoxy FRP's tensile, bending and compressive strength can reach more than 400Mpa. Note: Specific strength is intensity divided by density.
2. Good corrosion resistance
FRP is a good corrosion resistant material and has good resistance to the atmosphere, water and general concentrations of acids, alkalis, salts, and a variety of oils and solvents. Has been applied to all aspects of chemical preservation, is replacing carbon steel, stainless steel, wood, non-ferrous metals.
 3. Good electrical performance
FRP is an excellent insulating material used to make insulators. It can still protect good dielectric properties at high frequencies. Microwave permeability is good and it has been widely used in radome.
4. Good thermal performance
FRP has low thermal conductivity, which is 1.25~1.67kJ/(m•h•K) at room temperature, and is only 1/100~1/1000 of metal, which is an excellent thermal insulation material. In the case of transient ultra-high temperature, it is an ideal material for thermal protection and ablative resistance. It can protect space vehicles from escaping high-speed air currents above 2000°C.
5. Good design
①According to the needs, various structural products can be flexibly designed to meet the requirements of use, so that the product can have a very good integrity.
②Material can be fully selected to meet the performance of the product, such as: corrosion resistance, high temperature resistance, high strength in certain direction, good dielectric properties, etc.
 6. Excellent craftsmanship
①The molding process can be flexibly selected according to the product's shape, technical requirements, use, and quantity.
②The process is simple, it can be formed at one time, and the economic effect is outstanding. Especially for products with complex shapes and less molding, the process superiority is more prominent.
Can not require an FRP to meet all requirements, FRP is not a panacea, FRP also has the following deficiencies.
1. Low elastic modulus
The elastic modulus of FRP is two times larger than that of wood, but it is ten times smaller than that of steel (E=2.1×106). Therefore, the rigidity of the FRP is often insufficient in the product structure and it is easily deformed.
Can be made into a thin shell structure, sandwich structure, but also through high modulus fibers or stiffeners and other forms to make up for.
2. Long-term poor temperature resistance
General FRP can not be used for a long time under high temperature. The strength of general-purpose polyester FRP is obviously decreased above 50°C, generally it is only used below 100°C; general-purpose epoxy FRP is above 60°C, and the strength is obviously decreased. However, it is possible to select high-temperature resistant resins, so that long-term operating temperatures of 200 to 300°C are possible.
3. Aging phenomenon
Aging phenomenon is a common defect of plastics. FRP is no exception. It can easily lead to performance degradation under the influence of ultraviolet rays, wind and rain, chemicals, and mechanical stress.
4. Low interlaminar shear strength
Interlaminar shear strength is borne by the resin, so it is very low. The adhesion between layers can be improved by selecting a process, using a coupling agent, and the like. The most important thing is to avoid interlayer shear during product design.