PVC Resin

PVC resin, with the full name of polyvinyl chloride resin, is a kind of synthetic plastic polymer with large production volume each year. As a result, it is widely used in various plastic industrial fields. Polyvinyl chloride resin is a thermoplastic polymer compound formed by polymerization of vinyl chloride monomer(VCM) or dichloroethane(EDC) under the action of an initiator. Its main component is polyvinyl chloride. Meanwhile, adding some additives to enhance its heat resistance, toughness and ductility. Because of the characteristics of good chemical stability, corrosion resistance and water resistance, polyvinyl chloride is the most widely used raw material in plastic production. 

Before using PVC Resin to make finished products, we should convert it into compounds first by adding additives. As we all know, commonly used additives are heat stabilizers, UV stabilizers, plasticizers, heat modifiers, flame retardants, bactericides, foaming agents, etc.

1. It has the characteristics of abundant raw materials, mature manufacturing technology, low price, easy processing and wide application.
2. Flame retardancy is its greatest feature, so it can be used as the raw material for manufacturing of fire protection equipment.
3. It has good electrical insulating properties. So it can be used as low-frequency insulating material. In addition, its chemical stability is also good.
4. It has good mechanical properties. Tensile strength is about 60MPa. Impact strength is 5 ~ 10kJ/m2.
5. The degree of branching is small. The glass transition temperature is 77~90℃. And the decomposition starts at about 170℃.
6. The molecular weight of industrially produced PVC powder is generally in the range of 50,000 to 110,000. So it has a large dispersibility. The molecular weight increases with the decrease of the polymerization temperature. There is no fixed melting point. The powder starts to soften at 80-85℃, and becomes viscoelastic at 130℃. It begins to transform into a viscous flow state when the temperature is 160-180℃.  
7. Its stability to light and heat is poor. If it exceeds 100℃ or is exposed to sunlight for a long time, it will decompose to produce hydrogen chloride. And further autocatalytic decomposition will cause fading. Meanwhile, the physical and mechanical properties will also drop sharply. Stabilizers must be added to improve thermal and light stability in practical applications.
8. It can’t be used alone, but can be mixed with other ingredients to produce various products.

At first, many aspects (including raw materials, production process and operation) have a great influence on the quality of PVC.

In summary, viscosity number, apparent density, oil absorption rate, volatile matter content, sieving rate, number of impurity particles, heat aging whiteness, “fish eye” number, electrical conductivity, residual VCM content are the ten important parameters of general PVC resin powder.

In addition to the above indicators, polymerization degree distribution, particle size distribution, particle regularity, initial coloration, aging discoloration rate, dry fluidity, plasticizing rheological properties are all indicators for judging the quality of PVC products.

According to the production method, it can be divided into general-purpose PVC resin, high polymerization PVC resin, cross bonding polyvinyl chloride resin.

The general-purpose type is formed by the polymerization of vinyl chloride monomer under the action of an initiator.

High polymerization type refers to a resin polymerized by adding a chain extender to the vinyl chloride monomer polymerization system.

The cross bonding type is a resin polymerized by adding a cross-linking agent containing diene and polyene into the vinyl chloride monomer polymerization system.

According to the content of plasticizer, it can be divided into rigid PVC and flexible PVC. Without plasticizer, it is rigid PVC, and its glass transition temperature is as high as 80℃-85℃. So it is not easy to process. But after adding plasticizer, the glass temperature will decreasse, plasticity and flexibility will in crease and make it easy to process even at low temperature. Because the rigid type has good tensile, bending, compression and impact resistance, it can be used alone as a structural material. The flexibility, elongation at break and cold resistance of the flexible type will increase, while the brittleness, hardness and tensile strength will decrease.

The industry generally distinguishes PVC resin according to the method of obtaining vinyl chloride monomer. Depends on the polymerization method, PVC suspension resin is currently the largest variety, followed is the PVC paste resin made by emulsion method.

First thing to know, general-purpose type has a simple preparation method and a wide range of uses.

However, it also has some shortcomings. First, it can’t be adapted to high-end and special processing applications. Generally, high-polymerization polyvinyl chloride resin refers to PVC resin with an average degree of polymerization above 1700 or a slight cross-linked structure between the molecules. Second, this type improves the processing performance of general-purpose polyvinyl chloride resin. So it is more suitable for processing special soft products, high resilience, high toughness rubber products, as well as matte products. Third, this type can make the products with the characteristics of higher tensile strength, tear strength, elongation at break, abrasion resistance, high temperature and low temperature resistance, lower compression set, excellent plasticizer retention, etc.

According to the raw material, the production methods of polyvinyl chloride mainly include calcium carbide acetylene method, petroleum ethylene method and natural gas acetylene method. In addition, the main raw materials are monomeric vinyl chloride, dispersant, deionized water and initiator.

In general, there are three main methods for the synthesis of vinyl chloride monomer. 1. Ethylene oxychlorination with ethylene method with ethylene as raw material. 2. Synthesis of acetylene and hydrogen chloride from calcium carbide. 3. A method of using dichloroethane as a raw material and then cracking the dichloroethane into vinyl chloride.

Production fundamentals. Using calcium carbide as raw material, through three main chemical reactions of calcium carbide hydrolysis reaction, addition reaction of acetylene and hydrogen chloride, and vinyl chloride polymerization reaction. The production device includes reactor, fractionation process, separation process, etc. There are many types of equipment involved. Although the process control route is long, and the control parameters are more complicated. In actually, DCS automatic control help with all of these processes.

In brief, the K value is an index indicating the polymerization degree and molecular weight of polyvinyl chloride. In addition, the viscosity number is also an indicator of the molecular weight of the polymer. Since this product is an amorphous linear polymer compound, it is with various different characteristics. The larger the relatively molecular weight, the higher the viscosity, the better the strength, stiffness, toughness, heat and low temperature resistance of the material, but the worse the molding processability. On the whole, the difference in K value of polyvinyl chloride resin will have a certain impact on the processing technology and product performance. Therefore, when purchasing polyvinyl chloride resin, customers need to choose the suitable grade depends on the K value and applications.

By comparison, K70-75 PVC resin with high K value and higher molecular weight has the best mechanical properties. But it is more difficult to process.

In general, PVC resin k65/k66, PVC resin k67/k68 with suitable K value have a good balance between mechanical properties and processability. So they are the most popular and can meet the needs of the most PVC applications.

Compared to other types of PVC resin, K58-60 polyvinyl chloride with low value has the lowest mechanical properties and the processing is easiest. However, it has many difficulties in the application process.

• From the physical state, polyvinyl chloride paste is in the form of white fine powder. While the PVC resin is in the form of white fine particles.
• In terms of usage method. When using PVC paste resin to produce some products, you’d better mix it with appropriate amount of plasticizer. Additionally, it is in the form of liquid plastisol sometimes. Paste PVC resin is suitable for the production of flexible plastic products. Polyvinyl chloride resin is used after granulation with an appropriate amount of plasticizer. And it is generally suitable for the production of rigid plastic products.