ABS plastic – impact resistant thermoplastic material
ABS polymer is obtained by polymerization of acrylonitrile butadiene and styrene. Among the useful technological characteristics of the material, strength, surface gloss, easy coloring in the desired color, hardness and electrical insulating properties stand out. The main disadvantage is low resistance to ultraviolet radiation.
All constituents of acrylonitrile butadiene styrene are listed in the name of the compound. Three monomers are involved in the polymerization process, the proportions of which vary within the indicated ranges:
- acrylonitrile (15 – 35%);
- butadiene (5 – 30%);
- styrene (40 – 60%).
The production of 1 kg of ABS requires 2 kg of crude oil and consumes 26.5 kWh of electricity. Therefore, it is not a cheap material.
The industrial production of ABS is based on the radical copolymerization of styrene with acrylonitrile in the presence of rubber latex. For the proportion by weight of styrene/acrylonitrile monomers 76:24, a polymer of the same composition is synthesized. At other ratios, control of the homogeneity of the resulting product is required. Additionally, increasing the percentage of acrylonitrile dramatically increases the viscosity of the material.
The most widely used 2-stage emulsion polymerization in a continuous or periodic scheme:
First, latex is synthesized. The styrene and acrylonitrile monomers are added to the polybutadiene emulsion. The composition is stirred and heated to 50°C.
Then monomers emulsified in latex are grafted onto the rubber. For this, potassium persulfate or another water-soluble initiator is added and the mixture polymerizes.
The resulting suspension is degassed, filtered, dried and packaged.
For the production of ABS plastic with increased impact strength, a combined process is used. First, the synthesis is carried out in an emulsion or solution, and then in an aqueous suspension. This allows to put an additional amount of rubber.
The basis of the polymer is a rigid framework. The backbone is formed by a long polybutadiene chain with crossed short units of acrylonitrile and styrene. Nitrile molecules are polar. Therefore, the groups of this compound on adjacent chains are attracted, which increases the binding energy and the strength of the material.
In fact, two phases appear in the polymer. The hard core is formed by acrylonitrile and styrene. In this matrix, styrene-butadiene rubber granules 0.5–2 µm in size are distributed. They form the dispersed phase, which accounts for 15 to 30% of the total mass of plastic. Rubber granules contain occluded matrix copolymer microparticles and macromolecules of this copolymer grafted onto the rubber, which ensures interfacial interaction.
ABS polymer belongs to the class of engineering plastics. It is a plastic with high impact strength. Under mechanical action, the material is not destroyed, but undergoes plastic deformation. In terms of strength characteristics and mechanical rigidity, ABS is superior to various styrene copolymers, including ordinary and high-impact polystyrene. Another useful technological characteristic is wear resistance. The ABS polymer has an abrasion resistance of 110 cc. Other mechanical characteristics:
- density – 1.02-1.08 g / cc;
- the Brinell hardness number – 90-150 MPa;
- Charly impact test – 10-30 kJ/sq.m;
- tensile strength (35-50), bending (50-87), compression (46-80) MPa;
- elongation – 10-25%;
- moisture absorption – 0.2-0.4%;
- self-ignition temperature – 395°С;
- the Martens heat resistance – 86-96°С;
- softening temperature – 90-105°С;
- electrical strength – 12-15 MV/m;
- dielectric constant at 106 Hz – 2.4 – 5.0.
The operating temperature ranges for plastics vary. The interval where the polymer retains useful technological properties: from -20 to 80°C. This is a range that allows long-term use of ABS plastic products. The maximum allowable lower temperature limit is -40°C. Regarding the upper temperature limit, short-term heating of ABS plastic up to 100°C is allowed.
Acrylonitrile butadiene styrene polymer is resistant to solutions of acids, alkalis, inorganic salts. The plastic also has good resistance to hydrocarbons, lubricating oils, petrol and grease. The compound is soluble in acetone, ether, chloroethane, dichloromethane, benzene, aniline and anisole. ABS plastic is limited weather resistant, but is not UV resistant.
ABS plastic is highly weldable and has high dimensional stability, therefore it is recommended for precision casting. The polymer is easily processed mechanically, allowing:
- bending with the help of thermal strips;
The plastic has the ability to attach itself chemically to other ABS polymers and similar plastics. Additionally, the material is suitable for vacuum plating, contact soldering and electroplating. Plastic creates a shiny surface. The polymer is easily dyed in the desired color by introducing the appropriate pigments. Separate grades of plastic with high and low gloss are produced.
Combinations of ABS with other polymers are created to improve the technological properties of the material. The following composites are most in demand.
Impact-resistant amorphous material obtained with the participation of polycarbonate. Outperforms ABS in heat resistance. The indicator increases with an increase in the percentage of polycarbonate. As a result, the material withstands short-term heating up to 130-145°С (without loading) and 100-110°С (with loading). Glass-filled grades ABS/PC allow short-term heating up to 130-140°С. At the same time, the maximum continuous operating temperature is changed. The value is in the range of 60-95°C. Additionally, increasing the polycarbonate content increases impact and frost resistance. The brittleness temperature drops to -50°C.
The composite has good chemical resistance to alcohols, water, salt solutions and oils. Exposure to alkalis, aliphatic and chlorinated hydrocarbons can lead to cracking.
Finally, ABS/PC plastic is better processed – it is well welded by friction, hot plate, ultrasound, and is characterized by low warping.
The composition, combining ABS and PVC, has lower short-term heating temperatures. Values of 90-97°С are allowed. But the composite is characterized by improved resistance to weathering and aging.
The mixture of ABS and polybutylene terephthalate is a tough, impact-resistant amorphous or crystallizing material. The composite has good dielectric properties and is characterized by high dimensional stability at elevated temperatures.
Similar to the ABS/PS formulation, the material allows for adjustable heat resistance. With an increase in the content of polybutylene terephthalate, an increase in the parameter is observed. Plastic withstands short-term heating when loaded up to 85-150°C., the allowable temperatures increase to 150-200°C for glass-filled grades.
The material is resistant to aliphatic hydrocarbons, gasoline, oils and greases, dilute acids and alkalis, detergents. Increasing the ABS content reduces shrinkage and increases dimensional accuracy.
Plastic with a combination of ABS and polyamide. It also is an impact-resistant amorphous or crystallizing material. The ABS/PA6 composite is predominantly produced. This composition withstands short-term heating up to 180°C. Another modification – ABS/PA66, is characterized by an improved indicator (up to 250°C). In the absence of shock loads, the ABS/PA6 long-term operating temperature is 80-110°C. Under loads, the value decreases to 60-65°С.
Increasing the polyamide content increases the impact resistance of the material. Compared to ABS/PC and ABS/PVT, it has a lower density. The composite is resistant to cracking, well processed, perfectly reproduces the texture. ABS/PA plastic is characterized by high quality junctions – no loss of strength, connection lines are invisible.
ABS and elastomers
This composite allows to create materials with technological properties that are unattainable for individual polymers. Co-extrusion of ABS with thermoplastic elastomers increases the cost of manufacturing the material, but improves frost resistance, stiffness and resistance to weathering, oxidants and aliphatic hydrocarbons.