Research and development directions for PVC processing technologies and additives! ?

Polyvinyl chloride (PVC) is the main raw material for plastic building materials among chemical building materials. The consumption of PVC resin in China is increasing year by year: it was 980,000 tons in 1992 and 1.8 million tons in 1994. It is estimated that by the year 2000, China’s production capacity for PVC resin will reach 2.2 million tons per year. PVC resin is widely used in the construction industry; it not only boasts advantages of high quality and low cost in industrial production, but also finds application in residential construction, enhancing people’s living standards. 1 Application of PVC in pipes In 1994, polyvinyl chloride pipes accounted for 87% of plastic pipes used in construction [1], amounting to approximately 240,000 tons per year. It is estimated that by the year 2000, China will need 1 million tons of PVC pipes per year. PVC pipes are mainly of the straight-expanded type, with single and double-wall corrugated pipes and core-foamed pipes as supplements; other types of pipes are less common. An introduction to the development and application of new PVC pipe technologies is as follows. 1.1 PVC Core Foamed Pipe The PVC core foamed pipe is a composite pipe with a three-layer structure; the outer and inner layers are made of rigid PVC, while the core layer is composed of closed-cell, low-foam PVC. Its main components include PVC resin, CaCO3, blowing agents, and stabilizers. This product is lightweight, easy to install, and has a low cost. Its foam core layer effectively prevents the transmission of noise, it offers excellent electrical insulation, is impact-resistant, and has a long service life due to its corrosion resistance. 　　Among PVC pipes, straight-expanded PVC pipes are currently the most common, accounting for about 89%; single- and double-wall corrugated pipes account for about 8%, while pipes with a foamed core make up 3% [1]. Although core-foamed pipes account for a small proportion, they have been accepted by the market due to advantages such as light weight, low noise, and energy efficiency. According to surveys, many pipe manufacturers have made core-foamed pipes a priority for development in the near future. 1.2 PVC Transparent Reinforced Pipe Production Technology: It is manufactured by extruding two layers of plastic, with synthetic fibers inserted in between, resulting in good flexibility and the ability to bend. PVC transparent tubes possess good resistance to acids, alkalis, oils, and aging; they can replace rubber tubes and are inexpensive. It is widely used for transporting gases such as nitrogen, oxygen, and carbon monoxide, as well as liquids like water, dilute alkalis, and oils. It can also be used as pipes in water heaters, sprayers, gas stoves, etc. To build a production line with an output of 100 t/year, an equipment investment of 500,000 yuan is required, along with 1 million yuan in working capital. The comprehensive cost of the product is approximately 6,150 yuan per ton, while the market price is 10,000 yuan per ton [2]. 1.3 PVC double-wall corrugated pipe The PVC double-wall corrugated pipe is a new type of plastic pipe with a smooth inner wall and a hollow, corrugated outer wall; it is lightweight and easy to handle ； Features unique threading, variable wall thickness, and is pressure-resistant when buried underground ； It has corrosion resistance. Used as underground drainage pipes in Germany ； In the Netherlands, corrugated pipes are used for underground drainage, accounting for 97% of the pipes used in drainage systems ； Used in Italy for building electrical wiring. In the mid-1980s, China introduced advanced plastic bellows production lines [3]. 1.4 New types of CPVC engineering plastics In 1993, the American company Goodrich abandoned its PVC business and shifted to producing chlorinated polyvinyl chloride (CPVC). CPVC is obtained by further chlorinating PVC with a w(Cl2) of 57% to give it a w(Cl2) of 70%. Compared with traditional PVC, the heat distortion temperature (HDT) and flame resistance increase by 15%–40% and 16%, respectively. Dimensional stability improves, and the linear expansion coefficient decreases [4]. CPVC can replace metal and glass fiber pipes, conduits for transporting harsh liquids and air, pipes for hot and cold drinking water, and fire suppression pipes. It is now being introduced into new application areas, such as 61 cm diameter industrial pipes. These pipes can replace the fiberglass/PVC composite pipes and some stainless steel pipes currently used in industries like petrochemicals, and they can be used for sewerage pipes in urban construction. They offer significant economic benefits and have broad prospects for application. 1.5 Heat-resistant PVC resin A new type of heat-resistant vinyl chloride-maleimide copolymer resin has been recently developed abroad; in this resin, the ratio of vinyl chloride to maleimide is 87.6∶12.4. Heat-resistant pipes, sheets, and films can be produced; these products do not lose their color even when heated at 200 °C for 120 hours, and they have few fish-eye defects. Currently, the manufacturers that possess the production technology for this product are the American company B.F. Goodrich, as well as the Japanese companies Mitsui Toyo Chemical Company and Seiyu Co., Ltd. [5] 2 PVC Materials Enter Homes In the early 1990s, due to economic development and rising consumer standards, along with significant improvements in the production technology and product quality of polyvinyl chloride materials for household use, they began to be accepted by the market and entered various areas within households. 2.1 PVC Panels PVC panels, particularly the foamed variety, can compare with wood in terms of performance; they can be sawed, planed, nailed, and glued. They also have special advantages such as not deforming or cracking, and requiring no painting ； Low-foam boards can be welded and printed with ink, and can also be machined using methods such as sawing, drilling, and milling. 　　PVC foam boards are made from polyvinyl chloride as the main raw material, with the addition of foaming agents, flame retardants, and anti-aging agents, and are formed through extrusion using specialized equipment. It is widely used in industries such as construction, vehicle and ship manufacturing, furniture, decoration, renovation, advertising production, exhibition signs, urban aesthetics and environmental protection, as well as tourism. PVC foam boards are just emerging in our country; there are 3 manufacturing plants in Heilongjiang, Hubei, and Guangdong, with an annual total production capacity of less than 0.6 million tons. However, the domestic demand for PVC foam boards exceeds 300,000 tons, of which the total demand for foam boards with the skin attached accounts for about 60%, with 3 mm thick boards being the most widely used. In 1996, about 15 low-foam panel production lines were introduced in the country, with a production capacity of 45,000 tons per year [6]. 　　PVC low-foam sheet is a type of plastic sheet made from polyvinyl chloride as the main raw material, with various additives added; it is produced by extrusion through an extruder while controlling a specific degree of foaming. When joining these sheets in a planar manner, hot air welding can be used. The low-foam boards can be bonded to other materials over small areas in a very flexible and convenient manner, with a wide range of adhesives available, each offering different properties. Low-foam boards have excellent printability, and ink prints well on EPVC boards [7]. 　　Guangzhou Anwedi New Materials Co., Ltd., a Sino-foreign joint venture, invested 20 million RMB to introduce the UPVC low-foam board production line from the Italian company ITALPRODUCTS, in order to manufacture the lightweight Andy boards that were popular in Europe and America during the 1990s; it thus became the first enterprise in Guangzhou to produce such products. Lightweight Andy board is a technology-intensive, high-tech product known as wood-plastic board. Its density ranges from 0.6 to 0.7 g/ml, with dimensions of 244 mm×122 mm and thicknesses of 3 to 12 mm. It features moisture resistance, corrosion resistance, light weight without deformation, flame retardancy, and bright colors. It can be widely used in the decoration of subways and airplanes, as well as in various office spaces and homes with high aesthetic standards. It is also suitable for the production and fabrication of various luxury furniture, kitchenware, and bathroom fixtures. 2.2 PVC Plastic Decorative Doors and Windows This product uses heated PVC that is extruded and applied over wooden core profiles to create a very strong and durable protective layer. The material possesses good stiffness and strength, and it is resistant to peeling, does not require maintenance, and is flame-retardant as well as acid- and alkali-resistant. Insulated glass is used between the window sashes and the frame to ensure good thermal and sound insulation; it prevents frost and fogging in winter, and can raise the room temperature by 3–5 °C [8]. There are over 200 plastic door and window manufacturers in our country, with a production capacity of 210,000 tons. 　　Zhughua Group Company has introduced advanced foreign plastic-strengthened doors and windows production lines, producing 6,000 tons of high-quality PVC per year and assembling 100,000 square meters of premium plastic-steel doors and windows, with an investment of 120 million yuan. PVC lightweight plastic-steel relief doors use flame-retardant PVC as the surface layer; through processes such as gluing, heat pressing, and vacuum bonding, these doors possess properties such as fire resistance, moisture resistance, sound insulation, and thermal insulation. 2.3 PVC Paste Resin PVC paste resin has its own unique molding processes, such as coating, dip molding, and impregnation. It is easy to process, requires low investment in equipment, and possesses excellent foaming properties with uniform and fine bubbles. In the construction industry, it is used in 33% for producing wallpaper, and in 26% for manufacturing floor coverings. It can also be used to create metal coatings, industrial and consumer-grade synthetic leathers, molded boots, industrial gloves, flame-retardant conveyor belts, hot melt adhesives, waterproof membranes, and bottle cap gaskets. Coated PVC wallpaper has a three-dimensional, embossed appearance, as well as good matting properties and breathability. By 1990, China already had over 30 PVC wallpaper production lines [9]. 2.4 PVC Material Floors PVC hollow tongue-and-groove floors are coated with imported UV curing agents and treated with ultraviolet light; they offer advantages such as moisture resistance, fire resistance, wear resistance, and corrosion resistance. Their performance exceeds that of wooden floors, yet their price is only 1/3 of that of wooden floors with similar properties. Colorful quartz plastic floor tiles are made from quartz sand and PVC resin as the main raw materials. They feature bright and elegant colors, wear resistance, non-slip properties, flame resistance, aging resistance, good dimensional stability, and are also inexpensive. 2.5 PVC Wall Panels PVC wall panels are thin plastic profiles made by extruding PVC resin as the main raw material. Different from ordinary wall panels, they are used for various exterior wall decorations; of course, they can also be used for interior wall decoration. Currently, in countries such as the United States and Europe, PVC cladding panels are widely used for the exterior walls of residential homes, villas, and small to medium-sized public buildings. In China, only Hangzhou Hengtai Plastic Building Materials Co., Ltd. has introduced American equipment, molds, and technology to produce such exterior wall decoration panels. 　　The main raw materials for PVC wall panels, according to reference formula [10], are as follows: PVC resin – 100 g; chlorinated polyethylene – 8.0–1.8 g; organotin heat stabilizer – 1.2–1.6 g; titanium dioxide – appropriate amount; acrylic processing aid – 1.0–1.5 g; flame retardant – 1.5–2.0 g; paraffin – 1.0–1.5 g; calcium carbonate – 10.0–20.0 g; calcium stearate – 1.2–1.8 g; pigments – appropriate amount. 3. Applications of PVC in other industries 3.1 Water-emulsion type PVC elastic waterproof coating: The raw materials include coal tar, PVC resin, solvent, emulsifier, chemical additives, and water. The emulsion-type PVC elastic waterproof coating is mainly used for creating waterproof coatings on roofs with various slopes ； Seepage and moisture prevention in underground projects ； Leak prevention in kitchens and bathrooms ； It is more convenient for repairing leaks in existing buildings. The emulsion-type PVC elastic waterproof coating is a mixed paste that is applied to the surface to be coated during application; as the water gradually evaporates, the tar-gel particles come closer together and aggregate, and the small PVC molecules form larger molecular clusters, ultimately resulting in an elastoplastic coating. 　　For a plant with an annual production capacity of 1,000 tons, the equipment investment amounts to 50,000–80,000 yuan, while the working capital required is 300,000 yuan. The annual output value is around 2 million yuan, and the annual profit can range from 300,000 to 400,000 yuan [11]. 3.2 Rigid PVC transparent corrugated sheets Shanghai Delong Plastic Co., Ltd. is a large-scale plastic processing enterprise established with an investment of $6 million by two Japanese companies and Shanghai Plastic Industry Joint Company [12]; it specializes in the production of high-quality PVC corrugated sheets. Its advantages are that it is cheaper than glass, stronger, lighter in weight, and less prone to damage ； It is more aesthetically pleasing than fiberglass, offers better lighting, is more comfortable, and is safe and sophisticated. 4 Conclusion Polyvinyl chloride materials have a wide range of applications in the building materials industry. However, it is still necessary to produce various specialized grades of these materials through chemical modification and other methods, in order to replace expensive building materials. Moreover, it is important to continuously improve product quality and develop new varieties of PVC resins suitable for China’s national conditions, thereby promoting the development of the polyvinyl chloride industry.