By Ma Jie, China National Petroleum and Chemical Planning Institute (NPCPI)
Acrylic acid is one of the key downstream products of propylene and its annual consumption of propylene accounts for about 4% of the total in China. Acrylic acid is primarily used in the synthesis of various acrylic esters, and in the production of acrylates as well. The general-purpose acrylic esters mainly include methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), and 2-ethylhexyl acrylate (2-EHA). Acrylic esters are mainly used as a polymerization monomer in the production of coatings and adhesives, and are also widely used in the fields of printing inks, textiles and plastic additives. Acrylate (mainly sodium salt) homopolymer or copolymer has properties such as water absorption, water retention, cohesion, dispersion, thickening and bonding, widely used in the fields including sanitary materials, rural water retention and water treatment, oil exploitation, coatings, printing inks, textiles, printing and dyeing, paper, leather, and food processing.
1. High-performance acrylate emulsion
Aqueous acrylic ester resin (acrylic emulsion) is the fastest growing and most diversified pollution-free coating resin. The most popular grades of acrylate emulsions used in aqueous coatings include hydroxyl-containing acrylate emulsion, self-crosslinking acrylate emulsion, epoxy-modified acrylate emulsion, alkyd-modified acrylate emulsion, and fluorine-containing acrylate emulsion.
In the future, the acrylic emulsion research will be focused on the development of high-performance acrylate emulsion products, substitutes for solvent-based products in wider fields, and functional modified acrylate emulsion. It is expected that the acrylate emulsion market will have bigger potential in coating sector with supportive environmental protection regulations being issued in various countries and higher awareness of energy saving in the globe.
2. Specialty acrylic ester (monomer)
China's radiation curing (also known as ultraviolet curing) industry has developed rapidly in the past few years, greatly boosting the demand for specialty acrylic esters. In addition to the traditional coating sector, the radiation curing technology is applied in emerging application fields such as photolithography and 3D printing. Specialty acrylic esters (monomers) are classified into monofunctional acrylic esters (including high alkyl, specialty groups, and special structure) and multifunctional acrylic esters (i.e., bifunctional and trifunctional). There are more than 100 types of specialty acrylic esters that have been synthesized in the world. Their output, at about 200 kt on an annual basis, only equates to approximately 5% of the general-purpose acrylic ester production in the world, but they can include ester group with different length of carbon chain, as well as amino group, hydroxyl group, cyano groups, sulfonic acid group, epoxy group and furyl group in the structure, allowing them to have a diversification of properties.
3. Super absorbent polymer (SAP)
SAP is a low-crosslinking hydrophilic polymer compound with a loose network structure. It has been widely used in the production of disposable sanitary products such as infant diapers, feminine sanitary products, and adult incontinence products thanks to its good water absorption, moderate price and safety. However, China’s SAP industry has been plagued by excessive overcapacity in the past few years. The capacity in 2018 was about 1.3 million t/a, but the average operating rate was only about 50%. Conversely, the penetration rate of domestic sanitary products is low, making the total consumption of SAP still at a low level. As the central government has attached importance to the ecological environment construction, the domestic absorbent polymer industry has seen an investment wave in aspects of research & development and production. Accordingly, SAP has been stepping into the field of agriculture and forestry water conservation. In addition, SAP, as a concrete admixture, can effectively reduce the shrinkage of concrete. Hence it has become one of the research focuses by now and is expected to have wider application. To sum up, domestic SAP market will have huge development room in technology and product quality.
4. Acrylic rubber (ACM)
ACM is an elastomer copolymerized by acrylic ester monomers. It has excellent properties such as heat resistance, aging resistance, oil resistance, ozone resistance and UV resistance. As it is better than fluoro rubber and silicone rubber in terms of mechanical and processing properties, and better than nitrile rubber in heat resistance, aging resistance and oil resistance, ACM, as a kind of sealing material, has been widely developed and promoted across the automobile industry in recent years, especially in high temperature oil seal, crankshaft, valve stem, cylinder head gasket, and hydraulic oil pipeline of automobiles. Now, the domestic demand is almost covered by imports, with the annual import volume at over 4 000 tons. The import price is in the range of RMB60 000-70 000/t while the production cost of ACM is no more than RMB30 000/t, leaving huge margin room.
5. Acrylonitrile- styrene-acrylate copolymer (ASA or AAS)
ASA not only preserves degradation, aging, fading from ultraviolet radiation, but also resists decomposition or discoloration caused by high temperature generated in the oxidation process in the atmosphere. Thereby the adding of ASA greatly enhances the anti-aging and weather resistance to the products. Now ASA is widely applied in the production of synthetic resin tiles, electrical and electronic housing materials, automotive exterior materials, and outdoor building materials. A majority of domestic ASA resin producers are foreign-fund enterprises, largely depending on imports.
6. Ethylene-acrylic acid copolymer (EAA)
EAA has good low-temperature performance, good flexibility, big elasticity, excellent bending crack resistance and environmental stress crack resistance. It can replace ethylene vinyl acetate (EVA) in some application fields, as EAA has higher thermal stability and is a non-corrosive product that can accommodate a wider range of processing conditions. According to statistics, the annual consumption of domestic EVA is around 1.5 million tons, and the import volume is about 1 million tons. Nowadays, EAA is primarily used in the production of high-voltage cable shielding, hoses, packaging materials, adhesives, low-temperature sealing rings and accessories of household appliances. Besides, it can blend with olefin polymers or engineering plastics to enhance low temperature flexibility, environmental stress crack resistance and impact resistance as well. Ethylene-ethyl acrylate copolymer (EEA), a soft thermoplastic containing 5-20% of EA and with the degree of crystallinity lower than PE, is the most popular among EAAs.
7. Vinyl chloride-acrylate copolymer
Vinyl chloride-acrylate copolymer is a copolymer resin with excellent overall performance. Compared with general PVC resin, vinyl chloride-acrylate copolymer is superior in terms of impact performance and easy processing. At present, domestic vinyl chloride-acrylic copolymers mainly consist of vinyl chloride-acrylate random copolymers and vinyl chloride-acrylate graft copolymers. Acrylic ester/vinyl chloride graft co-polymer resin (AGR) is a representative product and is mainly used in the production of water supply pipe for its excellent impact resistance, stress resistance and seismic performance. It is expected that vinyl chloride-acrylate copolymer will have a bright future in line with rising household consumption and improving living quality.