Common modification methods and applications of PVC materials

Introduction to PVC Modification

Polyvinyl chloride (PVC or vinyl) is an economical and versatile thermoplastic polymer widely used in the construction and construction industry, production of door and window profiles, pipelines (drinking water and wastewater), insulation of wires and cables, medical equipment, etc. It is one of the world's top three thermoplastic materials, along with polyethylene and polypropylene. However, due to its poor processing and molding performance, such as high melt viscosity, poor fluidity, poor thermal stability, easy thermal decomposition, poor aging resistance, susceptibility to brittleness, hardening, cracking, poor toughness, and poor cold resistance, PVC modification is generally needed to make up for the above shortcomings.

Modification methods for PVC materials

▶ Chemical modification

Chemical modification includes copolymerization modification, grafting reaction, and chlorination.

1. Copolymerization modification: that is, allowing vinyl chloride monomer to undergo copolymerization reaction with other monomers. For example, copolymerization with monomers such as vinyl acetate, vinylidene chloride, acrylonitrile, acrylic ester, maleic anhydride, etc. to improve the processing performance, reduce the molding temperature, explore new applications, or appear as new materials.

2. Grafting reaction: Introducing another monomer group or another polymer onto the PVC side chain for grafting reaction. For example, ethylene vinyl acetate is grafted onto vinyl chloride to control the number and degree of polymerization of the grafted portion, thereby improving the impact performance, low-temperature brittleness, and aging resistance of this modified material.

3. Chlorination: PVC is chlorinated using the water phase suspension method (or gas phase method) to increase the chlorine content from the original 57% to about 65%. The purpose of this modification is to improve the heat resistance of PVC. The operating temperature is 35-40 ℃ higher than the original PVC, which is called chlorinated polyvinyl chloride (CPVC). The density of CPVC is higher than PVC, at 1.7 grams per cubic centimeter. Its flame retardant performance is better than PVC, and its tensile strength is also better than PVC. The disadvantage is that its impact strength is low. CPVC can produce products using extrusion, injection, and rolling methods. CPVC can be used for pipes, sheets, profiles, foaming materials, adhesives, coatings, modifiers, etc.

▶ Physical modification

Physical modification is the process of improving its performance by adding various additives or by filling, blending, and strengthening.

1. For example, adding ACR to improve the molding and processing performance of PVC materials; Add internal and external lubricants or polyethylene wax to improve the viscosity and flowability of materials; Adding heat stabilizers to improve the thermal stability of materials during forming and processing, and reducing their decomposition temperature; Adding antioxidants and anti UV agents to improve the aging life of products; Adding plasticizers to improve the plasticization performance of materials and increase the softness of products. Filler modification is the process of improving certain properties by adding inorganic or organic fillers.

2. If wood powder filler is added, reduce the specific gravity of PVC products to approach wood; Adding metal powders, such as copper powder and aluminum powder, to improve the conductivity of the product; Adding iron oxide magnetic powder to improve the magnetic properties of the product; Adding calcium carbide to improve product hardness while reducing material costs; Add red mud to improve the heat resistance and light aging performance of the product, while reducing material costs.

3. For example, other polymers that can be modified by blending with PVC include acrylonitrile butadiene styrene copolymer (ABS), methyl methacrylate butadiene styrene copolymer (MBS), polyacrylate, chlorinated polyethylene (CPE), ethylene vinyl acetate copolymer (EVA), nitrile rubber, ethylene propylene rubber, chlorinated polyvinyl chloride (CPVC), dioctyl maleate, etc.

In addition, PVC modification methods such as reinforcement modification, cross-linking modification, foaming modification, and radiation modification can also be used to improve the performance of PVC. For example, using mica powder with a high aspect ratio for reinforcement; Crosslinking modification with diisopropylbenzene peroxide (DCP) to enhance strength; Use azodicarbonamide foaming agent to reduce the specific gravity of PVC products, use cobalt radiation for irradiation, and improve strength.

Downstream applications of modified PVC materials

▶ PVC pipes

Due to the relatively low barriers to entry in plastic pipeline technology and funding, the overall entry threshold is relatively low. In recent years, a large number of small and medium-sized enterprises have flooded in, leading to serious homogenization of middle and low-end products and intense industry competition. PVC pipes were first promoted in China and are the most widely used plastic pipes. However, in the past two years, due to non-standard production operations and uneven product quality by some PVC pipe companies, the proportion of production has decreased. PVC pipes have advantages such as high compressive strength, good flame retardancy, high ring stiffness, excellent weather resistance, long service life, and easy installation. They are widely used in construction and municipal water supply and drainage, electricity, agriculture, communication, and other fields (mainly hard products).

In the future, there will be great development space for large-diameter solid walled polyvinyl chloride (PVC-U) pipes, high toughness PVC-M pipes, and medium and small diameter PVC-O pipes in PVC pipeline related products.

▶ PVC flooring

At present, PVC flooring in China is mostly used for public decoration, and is first tested in public places. It is mainly used in public areas such as schools, hospitals, and bus stops. PVC flooring has played a huge role in the fight against the epidemic. At the same time, it has also increased public awareness of PVC flooring, which is beneficial for the development of the domestic market after the epidemic. From the market demand situation in 2019, with the upgrading of consumption and the environment of secondary decoration, the development prospects of the sheet flooring market are promising. The continuous promotion of China's environmental protection concept has also brought opportunities for the market of new environmentally friendly and ecological buildings.

▶ PVC wood plastic wall panels

PVC wood plastic wall panel is a new type of environmentally friendly composite material, which is mainly made of bamboo powder, wood powder, calcium powder, PVC, and other raw materials, and is formed in one extrusion at high temperature. The surface of the wall panel not only features colorful patterns of materials such as wallpaper, paint, and stone, but also exhibits a high-end three-dimensional visual effect and a textured texture, making it a replacement product of wallpaper, paint, and stone. In the future, the development of PVC wood plastic integrated walls will gradually mature, and concepts such as top walls and whole houses will also be increasingly accepted.

▶ PVC soft membrane

Soft PVC film products have a thickness of 0.025-0.750mm and a width of ≤ 4m. PVC crystal board products have a thickness of 0.5-8.0mm and a width of ≤ 2m. The production of soft PVC rolling film generally uses suspension based universal PVC resin, with PVC SG-5 and PVC SG-3 being the most commonly used. In addition, PVC SG-7, PVC SG-8, PVC SG-1, PVC SG-0, and matte PVC resin are also used according to product requirements. In the current era of promoting high-quality development, PVC product production enterprises have increasingly high requirements for various resin indicators. Being able to subdivide product models and provide more PVC resin varieties will improve the quality of PVC soft rolling films and further consolidate their application in their field.