Plastic compounding

Plastic compounding 

Compounding is the process to mix various raw materials together to create a plastic product. Typical compounding process of thermoplastic material is conducted by extruders (most often co-rotating intermeshing twin screw extruders). The key to most compounding processes is to achieve best distributive and dispersive mixing and create a homogeneous mixture of each raw material. However, there are some special cases where balancing is needed. For example, in compounding long glass fiber products, you don’t want to break the glass fiber to achieve the best dispersive mixing. 

Why compounding

To mix with stabilizers

The most basic compounding operation is to compound the thermoplastic resin with stabilizers. Thermoplastic products in their simplest formulation are the neat resin compounded with stabilizers which include primary and/or secondary heat stabilizers, UV stabilizers if needed. 

To make color

For plastic materials, they are easily made into various colors by compounding the transparent colorless resin or white/off-white resin with colorants and pigments. Special visual effects, such as high gloss, reflective colors etc., can be achieved by compounding the resin with special colorants and fillers. 

To aid the next step in processing

Plastic materials are usually injection molded, extruded, thermoformed to make into shapes for various applications. These processes have specific requirements of material. For example, how easy the material flows at the processing temperature is an aspect for consideration. If the material is too viscous, the injection molding machine may not have the tonnage to push material into mold to form a high quality part. Compounding high molecular weight resin with low molecular weight resin at a ratio is a common way to adjust flow of the plastic materials. Also, flow promoter, mold release agent may be compounded with the resin to help the processing in the next step. 

Concentrates, or master batches, are also produced by compounding. The master batch will later be compounded or mixed with other ingredients to make the final product. The master batches help the material handling, ensure good mixing and accurate dosing of small percentage additives. 

To modify the plastic product

For many years, there has been no new plastic material (resin) introduced to the market. However, there are many ways to create new plastic products to meet customers’ needs by blending different types of polymer materials (polymer blends) and compounding the plastic resin with inorganic fillers (filled/reinforced plastics). 

One general category polymer blends are to improve the impact performance of the resin by blending the resin with impact modifiers which are also types of polymer materials, such as ABS, MBS, EP rubber, Acrylic impact modifiers etc.  For example, PC/ABS blend.

Plastic resins are also compounded with inorganic fillers to improve certain properties or reduce cost (some fillers are much cheaper than polymers.). Most common ones are filled with Talc or reinforced with glass fibers.

Another major category in plastic modification is to compound plastic resin with flame retardant additives to achieve flame retardancy required by customers and regulatory organizations such as UL. 

Compounding business

There are many companies focusing on compounding and modification of plastics. The compounding businesses do not need huge amounts of investment to start compared to resin manufacturers. Small businesses can start with just one twin screw extruder and accessory equipment such as feeders, pelletizers etc.. 

In the previous posts, when the resin manufacturers were listed, the compounders are left out if they are not upstream integrated.  During the pandemic, many companies faced supply chain issues and had difficulties getting the raw materials. When one searched the material on the internet, it would show many suppliers. However, if one company doesn’t have the resin production and only runs compounding business, most likely the company is facing the same situation with the short supply. 




PBT, the acronym for Poly(Butylene Terephthalate), is an engineering thermoplastic material that finds applications in automotive, electrical and electronics, medical devices, home appliances and industrial equipment. PBT is also used to make fibers for applications in tooth brushes, denim fabrics, and other textiles. PBT is one of the semi-crystalline thermoplastic materials, which means it will crystallize under normal processing (such as extrusion, injection molding, fiber spinning, etc.) conditions. As any crystalline polymer, PBT won’t crystallize 100%. The PBT material matrix is a mixture of crystalline and amorphous structures. 

If you are a mechanical keyboard enthusiast, you may know some of the keyboard caps are injection molded PBT material while others are made of ABS material.  PBT is also used to make the cooling fans for personal computers. 


PBT is synthesized through the polycondensation process, also known as the stepwise polymerization process,  which is different from the free radical polymerization process. As the name “stepwise” suggested, the PBT polymer chain grows by adding monomers, dimers, trimers and oligomers to the chain one step at a time. 

PBT is traditionally synthesized from DiMethylTerephthalate (DMT) and 1,4-ButaneDiOl (BDO) by releasing one methanol for each step of chain growing. As the purity of TerePhthalic Acid (TPA) improves, TPA is now used to polymerize with BDO to produce PBT. 

In the actual manufacturing process, BDO is overcharged to make the diesters, then followed by polycondensation to remove the excess BDO in the form of TetraHydroFuran (THF) as a byproduct. 


Resin manufacturer (upstream integrated, excluding compounders)

There are a few manufacturers of PBT resin out of the China region (they may also have manufacturing sites or compounding lines in China). They are listed in the Table below.

Key global PBT resin manufacturers

ManufacturersBrand Names
CelaneseCelanex, Vandar, Crastin
Mitsubishi ChemicalNovaduran
Radici GroupRaditer
LG ChemLupox
DSMArnite T

In China, There are a few PBT manufacturers:

  • Jiangsu Sanfangxiang Industry Co. Ltd. ; 30,000 tons/yr.  [1]
  • Sinopec Yizheng Chemical Fibre Co. Ltd.;  140,000 tons/yr + 120,000 tons/yr under planning.  [2], [3]
  • Kanghui New Material Technology Co. Ltd.; 160,000 tons/yr. [4]
  • China National BlueStar (Group) Co. Ltd.;  [5]
  • Chang Chun Plastics Co. Ltd.;  [6]
  • Xinjiang Blue Ridge Tunhe Polyester Co. Ltd.; 60,000 tons/yr. [7]
  • Jiangsu heshili New Material Co. Ltd.; [8]
  • WUXI XINGSHENG New Material Technology Co. Ltd.; 160,000 tons/yr. [9]
  • WEIJIAO holding group; 60,000 tons/yr. [10]















ABS is the acronym for Acrylonitrile-Butadiene-Styrene polymer, one type of thermoplastic materials. It is widely used as parts and enclosures in automobiles, home appliances, office equipment, medical devices, toys and more, thanks to its ability to achieve vivid color, high impact performance (including low temperature impact), excellent heat performance, easiness to plate and good resistance to household chemicals. ABS is one of the most popular materials in consumer 3D printing filament application along with PLA [Poly(Lactic Acid)].


As one can guess from the name, ABS is synthesized from 3 different of monomers acrylonitrile, butadiene, and styrene.       



Acrylonitrile (AN) Butadiene (BD) Styrene (ST)


Two processes are employed to manufacture ABS resin are:

  • Melt polymerization process
  • Emulsion polymerization process


Globally, ABS resin is manufactured in Asia, Europe, Middle East and North America. Some of the major global ABS resin manufacturer are: 

Key ABS Manufacturers (excluding Chinese companies in China)

ResinManufacturerCapacityPlant Location 1Plant Location 2Plant Location 3
ABSCHIMEI2.6M MTTaiwanZhenjiang, ChinaZhangzhou, China; 450KT
ABSLG ChemKoreanChina
ABSINEOS STYROLUTION600K MT in Ningbo, China; 50K T at Wingles, FranceGlobalNingbo, China
ABSELIX POLYMERS180K TTarragona, Spain
ABSTRINSEO80K T in ChinaZhangjiagang, ChinaTerneuzen, The NetherlandMidland, MI, USA
ABSSABIC140K T at JubailGlobalSaudi ArabiaUSA



China currently owns the largest market for ABS resin. For many years, China has to import significant amount of ABS to satisfy the domestic needs. However, the situation is changing. Huge amount of ABS resin capacity is being brought online. This is an incomplete list of companies currently have ABS plant in China.

  1. Liaoning Kingfa 600,000 tons/yr ABS finished mechanical installation, May 30th 2022. [1]
  2. Tianjin Dagu Chemical, 400,000 MT/yr.
  3. Guangxi Changke New Material (Keyuan Petrochemical), 400,000MT/yr. [2]
  4. Jilin Petrochemical, 600,000MT/yr in Jilin; 600,000MT/yr in Jieyang expected to be online in 2022. [3]
  5. Rongsheng Petrochemical and Zhejiang Petroleum and Chemical, 1,200,000MT/yr ABS project announced. [4]
  6. Shandong Haili Chemical Industry, 200,000 MT/yr. [5]
  7. SINOPEC Shanghai Gaoqiao, 225,000 MT/yr by 3 lines each 75,000 MT/yr, with 4th 75,000 MT/yr line planed to start 2024. [6]
  8. Shandong Lihuayi, 400,000 MT/yr.