Advances in ABS resin production technology

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ABS is a major thermoplastic engineering plastic, which is synthesized by copolymerizing more than 50% styrene along with appropriate amounts of butadiene and acrylonitrile. Styrene imparts rigidity and processability to the resin, acrylonitrile provides chemical resistance and thermal stability, while butadiene offers toughness and impact resistance. In 1998, the world’s ABS production capacity was 5.55 million tons, while consumption was 3.43 million tons. In 1998, the U.S. ABS production capacity was 855,000 tons, while consumption was 572,000 tons ； Western Europe’s ABS production capacity is 805,000 tons, while consumption is 640,000 tons ； Japan’s ABS production capacity is 791,000 tons, while its consumption is 417,000 tons ； Taiwan, China, has an ABS production capacity of 1.42 million tons, with a consumption volume of 253,000 tons ； South Korea’s ABS production capacity is 869,000 tons, while its consumption is 193,000 tons. In 1998, the main areas of consumption for ABS in Japan were household goods, appliances, general machinery, and automobiles ； The main areas of consumption for ABS in Western Europe are electronics and electrical appliances, household devices, and automobiles ； The main consumption areas of ABS in the United States are automobiles, appliances, building materials, and electronic devices [1–3]. 1. Current status and progress of ABS resin production technology 1.1 Technical overview There are many methods for producing ABS resin, and those that are widely used in industrial facilities around the world include the emulsion grafting blending method and the continuous bulk method. Over the past decade, two major advancements have taken place in the field of ABS resin production. The first is the significant success achieved in the development and industrialization of the emulsion-grafted bulk SAN blending process. The second is the gradual improvement of the bulk process, which has enabled the production of resin grades capable of penetrating certain markets. Table 1 lists the main production methods of ABS resin, as well as its current development status and prospects [4]. The emulsion grafting blending method was developed on the basis of the traditional production method for ABS resin, namely the emulsion grafting method. It is the earliest among the several ABS production processes used in industry, with the most mature technology and the widest range of applications. The emulsion grafting blending process includes three methods: emulsion grafting of SAN emulsions, emulsion grafting of suspended SAN, and emulsion grafting of bulk SAN. Through continuous improvement over time, this emulsion grafting blending process has become increasingly refined, resulting in stable production, a wide range of products, and excellent performance. In particular, the emulsion grafting method for blending SAN with the matrix is conducive to large-scale production and cost reduction; virtually all newly built large-scale ABS production facilities in recent years have adopted this production technology. The bulk process has been further improved in recent years, and it has gradually established itself as the primary method for ABS production. From the perspectives of environmental protection and investment, the bulk method is the best process for manufacturing ABS. The main drawback of the bulk process is its limited range of products, as well as the restricted performance of the goods produced. Research and development in recent years have focused on addressing these issues, and significant progress has been made; products manufactured using this process are gradually making their way into certain markets. Table 1 Main production methods of ABS resin, as well as their current development status and prospects. Main ABS production processes, current development status, and prospects: Blending method – a method that is no longer in use. Emulsion grafting method – has been replaced by the emulsion grafting blending method. Emulsion grafting/EMSAN blending method – still used in industry, but has been phased out in developed countries. Emulsion grafting/suspended SAN blending method – widely used in industry (especially in plants built before the mid-1980s). Although it is being replaced by the emulsion-grafted bulk SAN blending method, this approach remains more economical for small and medium-sized plants. The emulsion-grafted bulk SAN blending method has seen significant industrial development over the past decade, which facilitates larger-scale production and cost reduction; new large-scale ABS plants mostly employ this method, so its prospects are bright. The continuous bulk method has become the main method for ABS production in recent years, and as the range of products expands, it will become even more competitive in industry. The bulk suspension method is no longer used in developed countries, but it is still employed in some older plants in developing countries, mainly for producing sheet-form ABS resin. The emulsion suspension method is an improvement on the bulk suspension method, but the development of the emulsion-bulk method has not generated much interest in industry. The emulsion-bulk method attracted industrial interest after the 1980s due to its low costs, but several key technical issues remain unresolved, resulting in limited industrial application. The emulsion-grafted continuous bulk (emulsion-bulk) process was developed at the end of the 1970s and gained industrial attention in the 1990s. According to SRI’s estimates, the production cost of this process is lower than that of the continuous bulk process, but it causes greater environmental pollution than the continuous bulk process, and its construction costs are higher. In addition, other ABS production processes used in industry include the emulsion suspension method and the bulk suspension method. The emulsion suspension process was developed simultaneously with the emulsion bulk process, but it did not receive industrial attention. The bulk suspension process has been largely phased out in developed countries, but it is still used in some developing countries. 1. Emulsion grafting blending ABS process: The emulsion grafting blending process is the earliest industrialized technology among the various ABS production processes that are currently in use. It evolved from the emulsion grafting process, and depending on the differences in the SAN copolymerization process, it can be divided into three types: emulsion grafting of emulsion SAN blending, emulsion grafting of suspension SAN blending, and emulsion grafting of bulk SAN blending. Table 2 compares these three grafting blending methods for ABS production [4]; the latter two are more commonly used in current industrial facilities. Although the ontology process has gradually become the recognized more advanced and cost-effective ABS production method due to continuous improvements in recent years, the emulsion grafting and blending process remains the most widely used technology in production facilities around the world. The main reason for this is that the emulsion grafting and blending process is the most mature, offers the widest range of products, and has the greatest practicality. Table 2 Comparison of three grafting and blending methods for ABS production. In the process of producing ABS via emulsion grafting and blending, an elastomeric latex with a high rubber content is first prepared, and this latex is then used to undergo graft copolymerization with acrylonitrile and styrene to produce an ABS graft copolymer. SAN copolymers can be synthesized simultaneously with graft copolymerization, but the more common approach at present is to prepare them using emulsion, suspension, or bulk processes separately. Finally, by blending the ABS graft copolymer with the SAN copolymer in different proportions, various grades of ABS resin can be obtained. The three emulsion grafting and blending processes generally include the following intermediate production steps: preparation of the SAN copolymer, preparation of the butadiene latex, graft copolymerization of the butadiene latex with styrene and acrylonitrile, blending, and post-treatment. However, due to the differences in SAN polymerization processes, there are significant variations in cost, energy consumption, and product quality among the three emulsion grafting and blending processes. The emulsion grafting bulk SAN blending process has made significant industrial progress over the past decade due to its rational design, suitability for large-scale production and cost reduction, a wide range of products available, and high product quality; in recent years, newly built large-scale ABS resin manufacturing plants have basically adopted this process. The emulsion-grafted suspended SAN blending process is also widely used in production facilities around the world, especially in those built before the mid-1980s. It is believed that this process offers better economic benefits for small and medium-sized ABS plants. In the production of ABS resin blended via emulsion grafting, the core technologies are the synthesis of polybutadiene latex (EBR) and ABS grafting techniques; these processes involve a high level of technical complexity. Current research efforts are focused on improving the quality of the latex, reducing reaction time, and increasing the particle size of the latex. The quantity of grafted polymer rubber particles, as well as the structure and size of these particles, have a significant impact on the physical properties of ABS. Larger rubber particles (0.5μm) help improve the impact strength and processability of the resin, but they result in a reduced surface gloss of the molded products. On the other hand, ABS resin with smaller rubber particles exhibits higher surface gloss, but its impact strength is lower than that of ABS resin with larger particle sizes using the same amount of rubber. To enable ABS resin to possess both high surface gloss and high rigidity, rubber particles are typically required to have a bimodal particle size distribution; particles in the range of 0.2–0.65 μm generally yield resin that achieves a balance between these two properties. During grafting, latexes of different particle sizes are mixed in proportion according to the performance requirements of ABS. The particle size of polybutadiene latex prepared by conventional emulsion polymerization is around 0.1 μm, whereas the polybutadiene latex required for latex-grafted ABS generally needs to be at least 0.25 μm in size, with good particle dispersion and a narrow distribution. When increasing the particle size of polybutadiene latex during the normal polymerization process, the particle size increases by less than 0.01 μm per hour; it takes at least 40 hours to reach 0.3 μm. Therefore, extensive research has been conducted to reduce the reaction time required for latex production and to increase the particle size. This research can be summarized as polymerization-based size enlargement (one-step method) and post-polymerization agglomeration-based size enlargement (two-step method), with the latter further divided into chemical agglomeration and physical agglomeration [4]. (1) Scale-up of the polymerization process: The production process employed by Nippon Synthetic Rubber Company involves adding the materials to the polymerization reactor and carrying out polymerization at 60°C. When the polymerization conversion rate reaches 50%, 25 parts of butadiene are added, and the reaction continues until the conversion rate reaches 90%. The entire reaction takes 50 hours; the average particle size of the latex is 0.29 μm, with the concentration of precipitates being below 0.01%. Nippon Asahi Kasei Corporation added 0.5 to 5 parts of acrylonitrile during the emulsion polymerization of butadiene; due to its high hydrophilicity, acrylonitrile can form numerous micelles together with the emulsifier, thereby accelerating the polymerization reaction. At the start of the reaction, the amount of emulsifier used is 0.5 to 1.5 parts; a smaller amount of emulsifier can reduce the polymerization induction period. They control the particle size, particle size distribution, and agglomeration time by the timing of adding the emulsifier (at a conversion rate of 20%–50%), the amount of emulsifier used (0.3–0.7 parts), and the addition time. Its reaction time is 30 h, and the particle size is 0.2–0.5 μm [5,6]. The company also used the same formula and process to distribute the monomer across two formulations: the first formulation contained 20% of the total amount of monomer, while the second formulation contained 80% of the total monomer amount. As the polymerization reaction progressed for 2.5–5.0 hours, the second formulation was added continuously, with the overall polymerization duration being 14 hours. The monomer conversion rate was 97%, and the size of the latex particles was 0.165–0.20 μm [7,8]. It has also been reported that the addition of agglutinants such as sodium alginate and magnesium sulfate during the polymerization process can yield polybutadiene latex with a high solid content, high polydispersity, and large particle sizes. (2) Agglomeration amplification – Freeze agglomeration: The freeze agglomeration method involves feeding low-solid, small-particle-size (600–700 A) polybutadiene latex into a freeze drum; at the freezing point of the latex, the pressure generated by the freezing of water in the latex is used to cause the latex particles to agglomerate into larger particles. This method was industrialized by the American company Goodrich, and it has been used by both Japan Synthetic Rubber Company and Canadian Copolymer Company. Products obtained by the frozen agglomeration method are pure, easy to industrialize, and have a short reaction time; however, there are limitations in increasing the particle size, as only latex with moderate particle sizes can be produced. When latex is frozen, gel is precipitated, resulting in high power consumption. Pressure agglomeration is the process of causing latex to agglomerate under the action of a homogenizer. Although this method is old, some factories still use it effectively. GE’s process for increasing the particle size of polybutadiene latex involves preparing latex with a small particle size through batch polymerization in a single reactor over a reaction time of 15 hours; thereafter, continuous pressure aggregation is carried out, resulting in particle sizes of 0.3 μm, with the overall production cycle lasting 17 hours. Mechanical stirring agglomeration increases stirring intensity and also enables the production of latex with larger particle sizes. The reaction is carried out at 45–60°C; when the conversion rate reaches 40%–50%, stirring is intensified for 1 hour. At this point, the reaction conversion rate is 65%, and particles with a diameter of 0.44 μm or less account for 74.5%. Chemical agglomeration: By adding inorganic salts, acetic anhydride, and organic solvents such as propylene, benzene, toluene, and benzene-alcohol mixtures, as well as hydrophilic polymers like polyvinyl alcohol, polyethylene oxide, polyurethanes, polyethylene glycol, methyl cellulose, and polyvinyl acetal, agglomeration and amplification can be achieved. First, small-particle size latex was prepared, then 24 parts of 10% saline solution was added to the latex and stirred for 15 minutes, resulting in an increased particle size to 0.35 μm. Adding another 10% acetic anhydride solution yields latex with a particle size of 0.8 μm. The disadvantage of the agglomeration method is that the particle size after agglomeration is limited, it is highly affected by temperature and time, making it difficult to control and hard to repeat. Polymer latex agglomeration is a new type of agglomeration method developed in recent years, using polymer latex as the agglutinant. There are mainly two types of latexes used for this purpose: non-ionic surfactant latexes and α,β-unsaturated carboxylic acid copolymer latexes. Non-ionic emulsifier latex: Latex prepared from polyoxyethylene block copolymer non-ionic emulsifiers (POE-PS-POE) is used for agglomeration, which can significantly improve the agglomeration effect. To 100 g of latex to be agglomerated, 0.05–20 g of agglutinant latex is added, and stirring at room temperature for 1 minute to 1 hour completes the agglomeration process. The particle size can increase from 0.1 μm to 0.4–0.8 μm. The size and distribution of the agglomerated latex particles are related to the agglomeration conditions and the formulation of the agglutinant latex. The agglomeration effect is related to factors such as the molecular weight of the block copolymer and the solid content of the system. The larger the molecular weight of the block copolymer, the larger the size of the latex particles after agglomeration ； As the solid content increases, the agglomeration rate speeds up and the particle size increases. As the temperature increases, the particle size decreases. For example, when the temperature is 17°C, the particle size after agglomeration is 0.48 μm; at 65°C, the particle size becomes 0.3 μm. Generally, a temperature of 17°C is suitable for agglomeration. α,β-unsaturated carboxylic acid copolymer latexes: The most suitable for this category are copolymers of butyl acrylate and methacrylic acid. This latex causes the unsaturated carboxylic acid components to concentrate mainly on the surface of the rubber particles, thereby significantly enhancing the agglomeration effect. The carboxylic acid content ranges from 3% to 30%; below 3%, the agglomeration effect is not significant, while above 30%, the agglomeration effect becomes too strong, resulting in the formation of aggregates. To improve the agglomeration effect, a small amount of electrolytes such as KCl, NaCl, and NaSO4 can be added during the agglomeration process; the optimal pH for agglomeration is between 7 and 13. For polybutadiene latex with a particle size of 0.09 μm, an agglutinating agent latex [4] was prepared using the following formulation (by weight): butyl acrylate 80, methacrylic acid 20, potassium persulfate 0.5, NonsoTK–1 (semi-solid potassium soap) 2.0, Rapisol 80 (sodium octosulfobutyrate) 1.0, and water 200. The mixture was reacted at 70°C for 4 hours to produce the agglutinating agent latex. Then, 2 parts of this latex were added to 10 parts of polybutadiene latex, and the mixture was stirred at room temperature for 10 minutes, resulting in large-larger latex particles with a particle size of around 0.5 μm. Previously, Mitsubishi Rayon in Japan purchased all of its EBR latex from Renion and Sumitomo; now, 30% of it is polybutadiene latex with an enlarged agglomeration particle size developed internally. Polybutadiene latex with a particle size of 0.1 μm was prepared by batch emulsion polymerization, with a polymerization time of 15 h and a conversion rate of 95%. Agglomerant latex is a positively charged latex with a particle size of 0.1 μm, produced by the emulsion polymerization of two acrylic monomers. Small-particle polybutadiene latex is added to a tank equipped with a stirrer, followed by the addition of an appropriate amount of agglutinant latex; after stirring and mixing for 1 hour, latex with large particles of 0.3 μm is obtained. The Synthetic Rubber Plant of Lanzhou Petrochemical Company has made significant efforts to reduce the polymerization time of EBR latex; it has now completed an industrial pilot test that succeeded in shortening this time from 72 hours ± 4 hours to 50 hours ± 5 hours using a one-step process. The Research Institute of Lanzhou Petrochemical Company is also carrying out research on shortening the reaction time for EBR latex, and experimental results show that the reaction time for EBR latex can be reduced to 14 hours. 1.3 Continuous Bulk ABS Process The continuous bulk process for ABS resin was first developed by the Japanese company Mitsui & Co., and industrial production facilities were established in the mid-1980s. The bulk processing technique for ABS resin is very similar to that of HIPS; the main difference lies in the presence of another monomer—acrylonitrile. In recent years, the bulk process has been continuously improved and has established itself as the primary production method for ABS. The bulk process has advantages in terms of cost and environmental protection, but the construction cost of ABS production plants using this method is high, and there are limitations in terms of the range of products that can be produced. Conventional bulk polymerization processes cannot produce products with a rubber content of over 20%, so they have limitations in the production of high-impact ABS products. Furthermore, conventional ontology processes also have limitations when producing high-gloss products. Recent research and development efforts have focused on these areas; by continuously improving process technologies, the bulk processing technique has made significant progress in terms of the range of products it can produce, including:  Controlling the rubber particle size to less than 1.5μm and improving gloss.  Control the rubber particle size and morphology, improve impact resistance, increase the amount of filler in the rubber, achieve a bimodal particle size distribution for the rubber, and select the optimal type and concentration of initiator.  Introduce fourth monomer modification, such as the addition of α—**ethylene, to produce heat-resistant ABS resin. The rubber is crushed and dissolved in styrene and acrylonitrile monomers, after which it is combined with additives and/or a small amount of diluent (usually ethylbenzene, up to 5% by volume, to reduce the viscosity of the reaction mixture) and fed into the first reactor for polymerization. Typically, three vertical tower reactors are used in series, and no further monomers are added in the second and third reactors. Generally, a phase transition occurs at a conversion rate of 12% to 15%, at which point intense shear stirring is required, which has a significant impact on the particle size and distribution of the rubber. After the phase transition, the polymerization reaction takes place in the SAN phase and in the styrene-acrylonitrile particles embedded within the rubber particles; at this stage, only low-speed, non-shear stirring is required for the reaction. In the third reactor, the conversion rate of the monomer can reach around 95%; after the residual monomer is removed through a devolatilization step, the reaction products are sent for extrusion granulation. Additives such as lubricants and antioxidants are added to the molten polymer before granulation. The bulk polymerization process for ABS resin involves dissolving the elastomer in a mixture of styrene and acrylonitrile monomers to carry out a graft copolymerization reaction. In the early stage of the polymerization reaction, the rubber is partially grafted with styrene and acrylonitrile; at low monomer conversion rates, the SAN copolymer acts as a discontinuous phase. As more SAN is generated, the ratio of SAN to the rubber phase gradually increases; when this ratio ceases to change, phase transition begins, and the rubber phase becomes dispersed within the continuous SAN. Generally, the phase transition is completed when the conversion rates of styrene and acrylonitrile are 12%–15%, which mainly depends on the rubber content in the reaction system at the start of the reaction. The size of rubber particles is influenced by the stirring intensity, the viscosity ratio of the two phases, and the interfacial tension between the two phases. During the phase transition stage, the rubber is fully grafted, and the rubber particles are stably dispersed in the SAN copolymer, maintaining their size and shape throughout the entire subsequent polymerization process. The reaction is stopped once the monomer conversion rate reaches 70%–75%. Table 3 lists the advantages and disadvantages of the bulk polymerization process and the emulsion grafting blending process, while Figure 1 shows the continuous bulk ABS process flow [4]. Table 3 Comparison of advantages and disadvantages between bulk polymerization process and emulsion grafting blending process. Figure 1 Process flow of continuous bulk ABS production. In the traditional bulk process, the diene rubbers used are limited to low-molecular-weight polybutadiene rubbers with a high cis content; typically, polybutadiene rubbers with a glass transition temperature of -80°C or lower are employed. For ABS resins that require good toughness at low temperatures, it is preferable to use polybutadiene rubbers containing about 40% of cis 1,4 structures. Long-chain branched polybutadiene rubber with an average molecular weight of 180,000 to 260,000 is generally used. The bulk process differs from the emulsion process; the emulsion process is carried out in an aqueous phase, where the viscosity of the reaction system is low and heat transfer is good. When producing ABS resin using the bulk process, in order to make it easier to control the viscosity, the rubber content is usually kept below 15%, with a maximum of 20%. The low solubility of diene rubbers in monomers, especially acrylonitrile, also limits the rubber content in the resulting ABS resin. The grafting reaction occurs at the allylic position, and the degree of grafting depends on the properties of the initiator and chain modifier, as well as the differences in the solubility of styrene and acrylonitrile in the rubber and SAN phases. Differences in solubility lead to a decrease in the degree of grafting, as well as to varying amounts of acrylonitrile in the grafted rubber and in the SAN resin. Most patents related to bulk polymerization reactions specify the use of a diluent or solvent to reduce the viscosity of the reaction system, thereby making the polymerization process easier to control, especially when the conversion rate exceeds 60%. The most commonly used diluents are ethylbenzene and **Donghe toluene. Monsanto’s bulk process is an exception; its patents related to the bulk polymerization of ABS basically do not involve diluents. Most bulk process technologies employ a reactor system with 3 to 5 sequential reactors, and these reactors can be batch-type, column-type, tubular, or a combination thereof. Monsanto uses a continuous batch process with two reactors in series: the first reactor is a stirred tank type, while the second is a horizontal segmented constant-pressure reactor; no diluent is used in the reaction process. The rubber particles in ABS resin produced using conventional bulk process are larger, resulting in lower surface gloss. Some patents indicate that using PBR or styrene-butadiene block copolymer rubber with a very low molecular weight to prepare ABS homopolymer can increase the gloss of the product, but it reduces its notched impact strength. To achieve an excellent balance between surface gloss and impact resistance in the product, the particle size of the rubber in ABS resin must be less than 1.5μm. To meet this requirement in bulk polymerization, vigorous stirring is required during the phase transition, but this method leads to a significant increase in energy consumption. A patent describes a method to reduce the average particle size of rubber to less than 1.5 μm by chemically modifying the polymerization system: a chain transfer agent is added to the monomer mixture before the phase transition, so that at the time of the phase transition, the molecular weight of the copolymer is 0.8 times that of the diene rubber used. It is said that this method can be used under normal conditions, provided that the polymerization reaction takes place at a temperature of 110°C or lower, and that the rubber content does not exceed 10% (by weight). The impact resistance of ABS resin is closely related to the particle size and morphology of the rubber particles in the rubber-grafted polymer. Increasing the amount of SAN adhered to the rubber particles can increase their volume, thereby allowing the largest possible rubber surface area to be achieved with the least amount of rubber. This improves the efficiency of rubber use, with the ratio of volume percentage to weight percentage of rubber reaching as high as 5. Since the shape and particle size of rubber particles are formed during the phase transition, improving the conversion rate of monomers during this phase transition can enhance the impact resistance of ABS resin. By adding block SBR copolymers and SAN copolymers to the monomer rubber feed in the first reactor, the conversion rate in that reactor can be increased to 20%–45%. In this case, the block copolymers act as dispersants for the rubber phase, preventing the separation of the polymers trapped within the rubber; this ensures a higher amount of such polymers incorporated into the rubber, thereby enhancing the impact resistance of the product. Furthermore, the type and concentration of the initiator, as well as the diluent, also affect the morphology of the rubber particles. The initiators commonly used in the bulk polymerization of ABS are tert-butyl peroxoesters and organic peroxides. ABS resin, whose rubber particles exhibit a bimodal or multimodal distribution, possesses both high surface gloss and high toughness. There are two methods for producing this resin: one involves adding two batches of prepolymer during the bulk polymerization stage ； Second, the two ABS homopolymers are blended before degassing and granulation. Increasing the AN content in ABS resin from the usual 24% (by weight) to 27%–40% (by weight) results in smaller rubber particles within the ABS resin, thereby enhancing the product’s impact resistance and tensile strength. However, it is well known that as the proportion of acrylonitrile in the styrene-acrylonitrile monomer mixture increases, the solubility of the diene rubber decreases; the solubility of the diene rubber is 20% (by weight) when the acrylonitrile proportion is 0%, and it drops to 10% (by weight) when the acrylonitrile proportion is 42%. To overcome this drawback, the diene rubber can first be dissolved in styrene monomer, and then it along with acrylonitrile can be fed into the first reactor separately. Similar to the emulsion grafting and blending process, α‑**ethylene can also be used in place of styrene in continuous bulk polymerization processes to produce heat-resistant ABS modified resins; however, 15%–20% of the total amount of styrene monomers should be included to ensure that the product possesses good impact resistance and tensile strength. 1.4 Other ABS resin production processes Other ABS production methods used in industry include the bulk-suspension method, emulsion-suspension method, and emulsion-bulk method, etc. The bulk-suspension process has been largely phased out in industrially developed countries, but is still used in some developing countries. The emulsion-suspension process and the emulsion-mass process were developed around the same time, but did not receive industrial attention. Bulk-suspension process: This process developed alongside the bulk process; suspension polymerization helps to reduce the production difficulties that arise when the viscosity of the reaction mixture becomes too high at high conversion levels in bulk polymerization. Due to the development of emulsion-in-solvent technology in the mid-1970s, solvent-suspension technology did not receive significant industrial attention; however, it is still used in some older facilities, mainly for producing ABS resin required by the sheet market. The first few steps of the bulk-suspension process (rubber granulation, dissolution, and pre-polymerization with styrene and acrylonitrile) are the same as those in the bulk process. When a conversion rate of about 20%–30% is reached, the prepolymer is suspended in a liquid medium to complete the polymerization reaction. The polymer aggregation in the suspension, as well as the polymer recovery and post-treatment steps, are the same as those in the emulsion process. Emulsion-suspension process: The emulsion-suspension process was developed in the late 1970s; it is essentially an improvement on the bulk-suspension process. In the first step, emulsion polymerization is used to overcome the drawback of lower rubber content in the products produced by the bulk-suspension process. In the suspension process, the monomer is stably suspended in water in the form of spherical droplets thanks to a suspending agent; after polymerization is initiated by an oil-soluble initiator, the polymerization reaction takes place within each monomer droplet. Suspension polymerization is essentially a bulk polymerization reaction that takes place in a large number of “micro-reactors,” but the presence of water in the reaction system makes it easier to control the reaction temperature compared to bulk polymerization. Furthermore, since the products produced by this process are relatively large spherical beads, only one centrifuge is needed for separation, eliminating the need for complex separation processes such as coagulation required in the emulsion process. However, in recent years, as the bulk process has developed and improved, it has become a more attractive option; both the bulk process and the emulsion-bulk process are more economical than the emulsion-suspension process. Furthermore, controlling caking is necessary when transitioning from the emulsion process to the suspension process; this is a technically challenging issue that also hinders further industrial adoption of the emulsion-suspension process. Emulsion-sol process: The emulsion-sol process was first developed successfully by the Japanese company Toray. This process involves first demulsifying the grafted latex, and then carrying out continuous bulk polymerization to produce ABS resin. This method eliminates the need for separately preparing SAN and mixing it with the grafted latex in the emulsion grafting process, resulting in reduced energy consumption and lower production costs for the product. It is reported that the emulsion-solvent method has a 15% lower production cost compared to the emulsion-grafting suspension SAN blending method. However, this technology is not yet mature; some key issues, such as the extraction and separation processes involved in preparing the polymerization feedstock, have not been properly resolved. The performance of the resulting products, as well as their variety and grades, differ significantly from those obtained through emulsion grafting and blending processes. Therefore, its use in industry is still not widespread at present. 1.5 Economic analysis of the ABS resin production process: The American Chemical Systems Company conducted an analysis of the economic viability of the three most representative ABS production processes currently in use (see Table 4) [9]. These results were obtained by comparing the costs of producing ABS resin with a rubber content of 15% by weight in plants with an annual production capacity of 100,000 tons, based on the average prices in the Gulf region of the United States. Table 4 Comparison of the economic efficiency of ABS resin production processes (cents/pound). Table 5 Methods for improving the properties of ABS resin and their applications. The impact of the core latex on the properties of the resin is based on certain grafting formulas; if the grafting conditions change, the results may also change. Methods to change the grafting process include altering the amount of monomer surrounding the latex, and carrying out grafting by adding SAN emulsion together with polybutadiene latex ； Continuous addition of monomer and latex ； Change the initiator, etc. The resin must have an appropriate grafting rate to achieve high impact strength. The selection of ABS-grafted backbone latex depends on the glass transition temperature (Tg) and solubility parameter of the latex. To improve the low-temperature resistance of ABS, it is necessary to choose a rubber with a low Tg; generally, EBR latex (with a Tg of -86°C) is used. The gel content in the latex is also an important factor affecting the quality of ABS. To produce products with a good surface finish, it is necessary to choose latex with a high gel content ； Changes in the latex gel content are also related to the impact strength of the resins obtained from certain grafting formulations. Generally, as the gel content decreases, the impact strength increases. In the presence of agglomerated latex, the polymerization of styrene and acrylonitrile via an oxide reduction system at 35–45°C can prevent gel formation; it has been reported that this system reduces the tendency for the resulting ABS to discolor during molding. In addition to the highly functionalized ABS resins listed in Table 10, there are several development trends worth noting, such as antistatic ABS, electromagnetic shielding ABS, gas-barrier-resistant ABS, vibration-damping ABS, chemical-resistant ABS, ABS with reduced thermochromic properties, film-grade ABS, ABS with reduced notch growth, and high-fluidity ABS. 3. Current Status and Progress of ABS Resin Development in China 3.1 The Development Process of ABS Resin in China The research and development of ABS resin in China began in the early 1960s, and its development can be divided into a research phase, a development phase, and a period of rapid growth. 3.1.1 R&D Phase In 1963, the Synthetic Rubber Plant of Lanzhou Chemical Industry Company began research on the synthesis of ABS resin. By 1966, it had mastered the key technologies for ABS production. In 1975, the plant built China’s first ABS production facility using the grafting method, with a production capacity of 2,000 tons per year. The chemical plant of Shanghai Gaokiao Petrochemical Company also began research on ABS in the mid-1960s. In 1974, it built a 3,000 t/a ABS production facility using the suspension method; however, due to various problems with the process and equipment, this facility was not put into operation. In 1978, by employing an emulsion grafting-emulsion SAN blending process developed by the company itself, a 1,000 t/a ABS production facility was constructed. By the end of 1980, China’s production capacity for ABS resin had reached 3,000 tons per year, with a production volume of 3,300 tons per year. 3.1.2 Development Stage: China’s ABS production could not meet market demand. To accelerate the development of ABS resins in the country, production technologies for ABS were introduced gradually starting from the 1980s. In 1982, the Synthetic Rubber Plant of Lanzhou Chemical Industry Company introduced complete sets of technologies and equipment from Mitsubishi Rayon Company of Japan (ABS technology) and DuPont (polybutadiene latex technology), and built an ABS production facility with an annual capacity of 10,000 tons, which was put into operation in December 1984. In 1983, the chemical plant of Takahashi Petrochemical Company adopted technology and second-hand equipment from U.S. Steel Corporation (U.S.S.) to build a 10,000 t/a ABS production facility, which was completed and put into operation in May 1987. In 1986, the Organic Synthesis Plant of Jilin Chemical Industry Company (now Jihua Group Corporation) introduced a 10,000 t/a continuous bulk polymerization technology from Japan’s Toyo Engineering Corporation–Mitsui Toyo Chemical Corporation (TEC–MTC), and it was put into operation in December 1989. Thus, by the end of 1990, China’s ABS production capacity had reached 33,000 tons per year, with a production volume of 13,500 tons per year. 3.1.3 Rapid Development Phase By the 1990s, in order to accelerate the development of ABS in China and meet domestic market demands, the country placed great emphasis on the production of ABS resin, officially designating it as a key project that encouraged foreign investment. This led to a surge in investment by industries both domestically and internationally in building facilities for ABS production. Therefore, since the 1990s, the development of ABS resin in our country has taken three forms. (1) Technical upgrading of existing ABS production facilities: In 1993, Lanzhou Chemical Industry Company expanded an additional production line based on the 10,000 t/a ABS production technology it had introduced, raising the facility’s capacity to 20,000 t/a. Takahashi Petrochemical Company upgraded and expanded its 10,000 t/a ABS plant, increasing its capacity to 20,000 t/a, and it was completed and put into operation by the end of 1992. (2) Introduction of technology to build an ABS production plant: Daqing Petrochemical Complex introduced an ABS production plant with a capacity of 50,000 t/year, which was completed and put into operation in August 1997. Jilin Chemical Industry Company introduced an ABS production plant with a capacity of 100,000 tons per year; construction began on May 8, 1996, and the plant was completed and put into operation on October 20, 1997. Panjin Ethylene Industry Company introduced a 50,000 t/a ABS production facility, which was completed and put into operation in October 1998. (3) Joint ventures between domestic and foreign companies, as well as those between mainland China and Taiwan, to build ABS production facilities: South Korea’s LG Company partnered with Ningbo Yongxing Chemical Factory to establish Ningbo LG Co., Ltd., whose ABS production capacity is 50,000 tons per year; the facility was put into operation in 1998 ； Taiwan’s Guoqiao Company established a joint venture in Zhenjiang, with an ABS production capacity of 50,000 tons per year; it came online in 1998. In China, starting with the construction of an ABS production plant with a capacity of 0.2 ten thousand tons per year by Lanzhou Chemical Industry Company in 1975, the total production capacity had reached 340,000 tons per year by the end of 1998. 3.2 ABS Resin Production Technology in China At present, the technologies used in ABS production facilities in China include: emulsion-grafted suspended SAN blending, emulsion-grafted emulsion SAN blending, continuous bulk process, and emulsion-grafted bulk SAN blending processes. Since the first two sets of ABS plants built in our country using domestically developed technology have been shut down, all currently existing ABS plants have been imported from abroad. The ABS plants introduced in the mid-to-late 1980s, with the exception of Jihua Company’s 10,000 t/a continuous bulk ABS plant which, due to issues such as immature technology, now largely stops producing ABS resin, are all the main drivers for ABS resin production today. The process technologies used in the ABS plants introduced in China since the mid-1990s represent the current world’s advanced standards, and they will enable a significant leap forward in the industrial production of ABS resin in China after nearly a decade of stagnation. 3.2.1 Emulsion-grafted suspended SAN blending process: In 1982, the Synthetic Rubber Plant of Lanhua Company introduced a production facility for manufacturing ABS via emulsion-grafted suspended SAN from Japan. The original design capacity of this facility was 10,000 tons per year; in 1992, its capacity was increased to 20,000 tons per year following modifications. The polybutadiene component of this process utilizes patented technology from Japanese company Toray, with a polymerization time of 72 hours ； The ABS portion utilizes technology from Mitsubishi Rayon Company in Japan. “During the Eighth Five-Year Plan period, Lanhua Company conducted research and development on various key technologies in ABS production. In the field of EBR latex synthesis, techniques such as a one-step method for synthesizing large-particle EBR latex, a freeze-agglomeration method for producing large-particle EBR latex, technologies to reduce the synthesis time of EBR latex, and engineering scale-up studies on butadiene polymerization reactors have been developed. In terms of ABS grafting, grafting techniques for ABS grafted latexes with rubber contents of 15%, 25%, 45%, 60%, 65%, and 70% have been developed successively. To further reduce the EBR polymerization time, multi-grade EBR latexes with particle sizes of 700–1000 Å and 3000–5000 Å, and gel contents of 0–5%, 30%–40%, 50%–70%, and 70%–85% have been recently developed to meet the requirements of various grades of ABS. As a result, the reaction time has been reduced from 50 hours to 14–20 hours, reaching an advanced level in China. The industrialization of grafting technology with rubber contents of 65%, 70%, and 75% has been achieved ； Increase the grafting rate ； Preparation of core-shell structured graft powder ； High-gel grafting technology is utilized to control the gelation and particle size of the grafted backbone; a third monomer is introduced, MgSO4 is used as a coagulant, the washing process is optimized, and a suitable combination of antioxidant systems, heat stabilizers, and drying conditions are selected to improve the appearance of ABS. 3.2.2 Emulsion Grafted Emulsion SAN Blending Process: In 1983, Takahashi Petrochemical Company introduced from U.S. Steel a plant for producing ABS using emulsion grafted emulsion SAN (equivalent to the technology level of the late 1970s worldwide). This facility is a second-hand unit with a design capacity of 10,000 t/a; it was upgraded in 1992, increasing its production capacity to 20,000 t/a. Advantages of this method: the grafting rate is easy to control, and multi-product production is possible. Disadvantages: This method has the same drawbacks as the conventional emulsion polymerization grafting method, requiring two sets of polymerization equipment. Takahashi Petrochemical Company acquired used equipment, which suffers from frequent malfunctions in the machinery and instruments, low-level software, unstable production, and poor product quality. 3.2.3 Continuous bulk polymerization process: In 1989, the Organic Synthesis Plant of Jihua Company introduced an ABS production unit using the continuous bulk method from Mitsubishi Tokuyu of Japan. This process is similar to that used for HIPS production; uncrosslinked rubber is dissolved in styrene and acrylonitrile monomers, pre-polymerized until a phase transition occurs, and then bulk polymerization continues. To reduce the high viscosity during polymerization, a small amount of ethylbenzene is added as a solvent. The plant’s capacity is 10,000 tons per year, and according to the original design, it can produce 8 different ABS product grades. However, due to the immaturity of this technology, the product quality standards are low; the products can only achieve moderate impact strength, there are few grades available, and some auxiliary materials must be imported. For these reasons, this facility is currently used mainly for producing HIPS resin. Advantages of this method: continuous production, simple process, short workflow, and high adaptability ； Fewer devices required, lower investment costs, less use of chemicals, fewer waste streams, low energy consumption, and reduced production costs ； It features easy product variety switching, high product quality, simple operation, and the ability to produce HIPS, SAN, and others as well. Disadvantages: It is difficult to produce products with a high gel content; in other words, high-impact strength ABS resin cannot be manufactured, only ABS with moderate impact strength can be produced, resulting in a relatively limited range of products. 3.2.4 Emulsion-grafted bulk SAN blending process: All 5 large-scale ABS production facilities introduced in China recently employ the emulsion-grafted bulk SAN blending process technology. Although the new plants, like those at Lanhua Company and Takahashi Petrochemical Company, also use the emulsion process to produce grafted polymers and obtain ABS products through blending, the difference is that their SAN pellets are produced using the bulk polymerization process. This reduces the amount of impurities in the products, resulting in purer products with improved performance. It also leads to less wastewater being generated during production, thereby reducing production costs. These process technologies represent the more advanced ABS resin production methods in the world today. The mixing process flow for emulsion-grafted bulk SAN is shown in Figure 2. Figure 2: Mixing process flow for emulsion-grafted bulk SAN. The ABS production facility of Jihua Group Corporation has 2 production lines, with a capacity of 50,000 tons per year per line. The particle size of the polybutadiene latex is 3000 A, the reaction time is 20–33 hours, and the conversion rate is 90%. When producing high-impact products, large-particle styrene-butadiene latex (provided by JSR Corporation) must be added. The production of ABS grafted powder utilizes 3 grafting reactors, with a reaction temperature of 40–90°C and a reaction time of 8–11 hours; the rubber content in the grafted powder is 40%–60%. The SAN synthesis utilizes the continuous bulk process technology of TEC—MTC Company. In the ABS unit of Daqing Petrochemical Complex, the polybutadiene latex is produced by emulsion polymerization in 4 polymerization reactors, at a reaction temperature of 50–70°C and a reaction time of 25–45 hours, with a conversion rate of 95%–99.5%. The grafting reaction of the ABS emulsion was carried out in 4 polymerization reactors, at a reaction temperature of 60–90°C and a reaction time of 10–14 hours, with a conversion rate of 98%. ABS grafted latex undergoes three-stage coagulation, and then is dehydrated using a centrifuge and dried in a fluidized bed dryer to yield ABS grafted powder with a moisture content of around 1%. SAN resin utilizes Cosden Company’s continuous bulk process technology. Advantages of the emulsion grafting bulk SAN blending process: there is no limit on the amount of rubber used, which facilitates the production of highly impact-resistant products ； The grafting rate is easy to control, and the product performance is stable ； The product quality is purer compared to conventional emulsion-grafted products ； Adjusting the mixing ratio of ABS powder and SAN pellets allows for the production of multiple grade products ； The production of SAN using the bulk polymerization method requires low energy consumption. Disadvantages: Two sets of processes and equipment are required; there are many post-treatment steps after producing ABS powder, and the operation is also complex ； Impurities caused by emulsifiers, coagulants, and the like in the product have not yet been completely removed. The 100,000 t/a ABS production plant of Jihua Group not only features a larger scale but also adopts an emulsion grafting–modified bulk SAN blending process, which significantly reduces production costs. It achieves a 12.7% reduction compared to the emulsion SAN blending method used by Takahashi Petrochemical Company, and a 10.2% reduction compared to the suspension SAN blending method used by Lanzhou Chemical Industry Company. This approach also helps to improve product performance and the color of the products. It should be noted that the process of producing ABS via continuous bulk polymerization is not yet widespread; therefore, the method of emulsion grafting combined with bulk SAN blending represents the best approach for ABS production. This post was last edited by dm88440 on 2009-2-13 16:08.]