What Is High Impact Polystyrene?

High impact polystyrene, also known as HIPS, is a thermoplastic material made of elastomer-modified polystyrene. The two-phase system consisting of a rubber phase and a continuous polystyrene phase has developed into an important polymer commodity in the world. This universal product has a wide range of impact properties and processing properties, making it widely used. , Such as used in the automotive, equipment, electrical products, furniture, household appliances, telecommunications, electronics, computers, disposables, medicine, packaging and entertainment markets.

Chinese name: High impact polystyrene
English name: High impact polystyrene
nickname: HIPS

Water soluble: Oil and water resistant, soluble in benzene, toluene, ethyl acetate, dichloroethane and other organic solvents.
Density: Relative density 1.04-1.06 g / ml
Exterior: White opaque beads or particles

High Impact Polystyrene

Polystyrene is one of the oldest industrially produced thermoplastic polymers and has a very versatile product for a wide range of uses. The advantages of this bright, pure amorphous plastic are easy to process, rigid, dimensionally stable and transparent, but its low impact strength limits its application.

For high-impact polystyrene, a small amount of polybutadiene is bonded to the polystyrene matrix. It has a "sea island structure", the matrix is plastic, and the dispersed phase is rubber. Has many characteristics:

1. Impact-resistant polystyrene is a thermoplastic resin;

2. Odorless, odorless, hard material, good dimension stability after forming;

3.Excellent high dielectric insulation;

4. Non-quality low-absorbent material;

5. Its gloss is good and easy to paint. ^[1]

Production method of high impact polystyrene

HIPS has two basic processes: batch and continuous processes. Both processes generally use prepolymerization first. After the prepolymerization is completed, the polymerization is continued in a suspended form in a batch process, and the polymerization is performed in a solution form in a continuous process. Therefore, the batch process is also called bulk suspension process, and the continuous process is also called solution process. ^[2]

HIPS Elastomer for high impact polystyrene HIPS

There are two main types of elastomers commonly used, one is low-cis polybutadiene rubber and the other is high-cis polybutadiene rubber.

Low cis polybutadiene (LCBR) is obtained by the polymerization of butadiene initiated by alkali metal, alkyl lithium or other negative ion polymerization initiator. The content of cis structure of polybutadiene is usually around 40%. The trans structure content of LCBR is generally around 50%, and the structure content of 1,2 is generally around 10%. The three structures are randomly distributed. LCBR has a narrow molecular weight distribution, Poisson distribution, low branching, excellent cold resistance and low temperature flexibility, and has the advantages of good color, transparency, and uniform quality. LCBR is the first choice for HIPS impact modified rubber. This is mainly because LCBR has the following characteristics: (1) LCBR chain structure contains 8-20% vinyl. Compared with the internal double bond of cis-1.4 structure and trans-1.4 structure, it has higher cross-linking ability, is easy to produce graft or cross-linking, and its tertiary and secondary carbon atoms on allyl groups are also easy. Graft reaction occurs. The reactivity of the vinyl structure of LCBR is twice that of the trans-1.4 structure and four times that of the cis-1.4 structure. When it is used to produce ABS and HIPS, it can be directly or thermally initiated without adding or using initiators. (2) The gel content of LCBR is extremely low, usually less than 0.01%. (3) LCBR does not contain transition metals, so it has good aging resistance. (4) LCBR raw rubber is easy to cut without sticking knife, and its dissolving performance in styrene is good.

As the high-cis polybutadiene rubber, a nickel-based catalyst or a cobalt-based catalyst can be used. The nickel-based polybutadiene rubber refers to a polybutadiene obtained under the action of a catalyst using a metal nickel compound as a main catalyst. Usually the main catalyst is nickel carboxylate, such as nickel naphthenate, nickel octoate, nickel benzoate, etc .; the cocatalyst is an organometallic compound, whose role is to reduce the valence of nickel and alkylate it. Commonly used is triethylaluminum. , Tributylaluminum, triisobutylaluminum, diethylzinc, etc .; The third component is a halogen-containing compound, which is used to provide halogen or electronegative groups. Commonly used are hydrogen fluoride and boron trifluoride ether complex. Compounds and boron trifluoride butyl ether complexes. The catalytic system used in our industry is nickel naphthenate / triisobutylaluminum / boron trifluoride ether complex. Nickel catalyst belongs to the coordination polymerization mechanism, and its orientation is strong. The cis-1,4-configuration content of the prepared polybutadiene rubber is as high as 96%, which is much higher than that of lithium-based low-cis polybutadiene. Rubber (LCBR), its 1,2-configuration content is only about 1%, which is much lower than LCBR. The equivalent period of cis-1,4-polybutadiene is long, 0.86nm, and the carbon-carbon single bond in the molecule is easier to rotate, especially the single bond next to the double bond is easier to rotate internally when the shadow of the double bond is downward. The chain has good flexibility. Under normal conditions, the molecule is in a curled state and has good resilience; while trans-1,4-polybutadiene, isotactic 1,2-polybutadiene, and syndiotactic 1,2- Polybutadiene has shorter equivalent cycles of 0.49nm, 0.65nm, and 0.514nm, respectively. The molecular chain has poor flexibility, is easy to crystallize, and has low elasticity. Therefore, the high-cis nickel polybutadiene rubber has excellent elasticity. Cis-1,4-polybutadiene can be oriented to induce crystallization during stretching, which also imparts high strength characteristics to nickel-based butadiene rubber. Therefore, the use of high-cis polybutadiene rubber for HIPS production can make HIPS better toughness and strength.

Cobalt-based catalysts refer to a type of catalytic system based on any soluble and insoluble cobalt compounds, such as cobalt chlorides, oxides, organic acid salts, and pyridine complexes. Like nickel-based catalysts, cobalt-based catalysts also belong to the coordination polymerization mechanism and have strong directivity. When used for butadiene polymerization, cis-1,4 is usually obtained when alkyl aluminum halide is used as a cocatalyst. -High cis-polybutadiene with a configuration content of 96-98% and a 1,2-configuration content of 1-2%. In addition, water, organic peroxides, halogens, alcohols, and organic halides are usually added as the third component activator to improve the activity of the catalyst. The catalytic system used in industry is a cobalt octoate / monochlorodialkylaluminum / water ternary system. Like nickel-based polybutadiene rubber, the higher content of cis-1,4-configuration in cobalt-based polybutadiene rubber will give it excellent elasticity and high strength, which in turn will provide stronger toughness and strength. Cobalt-based polybutadiene basically does not contain gel, and its degree of branching is usually about 0.8, which is significantly higher than that of nickel-based, titanium-based and rare earth polybutadiene. This feature makes cobalt-based polybutadiene rubber have good solubility in styrene, so cobalt-based polybutadiene is suitable for producing HIPS rubber. ^[3]

High impact polystyrene performance

HIPS has the dimensional stability of General Polystyrene (GPPS), and has better impact strength and rigidity. ^[4]

The relative density of HIPS is 1.04 ~ 1.06, and the heat distortion temperature is 70 ~ 84 . HIPS has a tensile strength of about 15 to 30 MPa and an elongation of 35 to 60%. It increases with decreasing temperature and increasing strain rate, a bit like a rubber toughening system. HIPS behaves a bit like a viscoelastic solid, which can creep when exposed to constant tensile stress. Creep decreases with increasing molecular weight and usually increases with increasing rubber content. The creep behavior of HIPS is strongly dependent on the average molecular weight (Mw). The bending strength is 29.4 ~ 50 MPa, the impact strength is 0.09 ~ 0.16N / M, the Vicat softening point is 84 ~ 100 , and the melt index is 2 ~ 9g / 10min. The heat resistance of HIPS parts depends on their shape, production conditions, type of heat source, and duration of heating, and is also affected by the level of HIPS.

The properties of HIPS are not affected when exposed to water, alkalis and dilute mineral acids. It can be swelled by some organic solvents and dissolved by others, which is determined by the difference in the dissolution parameters between the continuous phase and the solvent phase. HIPS is particularly vulnerable to damage when exposed to chlorinated and aromatic hydrocarbons. ^[4]

Causes of high impact polystyrene impact resistance

Impact-resistant polystyrene is an impact-resistant polystyrene product produced by adding polybutadiene rubber particles to polystyrene. This polystyrene product adds micron-sized rubber particles and connects the polystyrene and rubber particles together by grafting. When impacted, the stress at the tip of the crack propagation is released by the relatively soft rubber particles. Therefore, crack propagation is hindered, and impact resistance is improved.

High impact polystyrene

Because of its ease of manufacture and low cost, HIPS is widely used in many appliances and industries. Major industries and markets include packaging, disposables, appliances and consumer appliances, toys and entertainment, construction products and decorations. The biggest single application of HIPS is packaging, especially in the food industry. Consumption in the world exceeds 30%. ^[4]