POLYSTYRONICS - GPPS, HIPS, EPS, ABS

Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle.

STYRONICS POLYMER FAMILY

Styrenic polymers include:

Polystyrene (PS) – General-purpose plastic used in packaging, disposable containers, and insulation.
Expanded Polystyrene (EPS) – Foam applications (e.g., packaging, food containers).
High-Impact Polystyrene (HIPS) – Toughened PS with rubber additives.
Styrene-Butadiene Rubber (SBR) – Used in tires, footwear, and adhesives.
Acrylonitrile Butadiene Styrene (ABS) – Engineering plastic for automotive parts, electronics.
Styrene-Acrylonitrile (SAN) – Transparent, rigid plastic for bottles and containers.
Styrenic Block Copolymers (SBCs) – Thermoplastic elastomers (e.g., SBS, SEBS) used in adhesives, footwear, and medical devices.

PROCESS METHODS

Free Radical Polymerization: It involves the initiation, propagation, and termination of free radicals.

Bulk Polymerization: Pure styrene + initiator → clear PS (used for optical applications).
Suspension Polymerization: Monomer droplets in water → PS beads (for EPS foam).
Emulsion Polymerization: Latex form → used for SBR rubber and coatings.

Anionic Polymerization: This method uses an anionic initiator (e.g., butyllithium) to initiate the polymerization. Characteristics: Produces polystyrene with a very narrow molecular weight distribution (monodisperse). Applications: Used for specialty polystyrene with high purity and controlled molecular weight.

TYPICAL BULK POLYMERIZATION

Styrene is polymerized in the absence of a solvent or dispersing medium.

Process: Styrene monomer is mixed with a free radical initiator. The mixture is heated to initiate polymerization. The reaction is exothermic, and temperature control is critical. The polymer is cooled and extruded into pellets.

Advantages:

High purity product.

No solvent recovery required.

Disadvantages:

Difficult to control temperature due to exothermic nature.

High viscosity at high conversion rates.

HIGH IMPACT POLYSTYRENE PROCESS

Typical Industrial Process Flow

Feed Preparation – Styrene + polybutadiene rubber + initiator (e.g., peroxide).
Pre-polymerization – Partial conversion in a stirred tank (to reduce viscosity).
Plug Flow Reactor – Multi-zone temperature control (e.g., 80°C → 120°C → 160°C).
Devolatilization – Remove unreacted monomer via vacuum extrusion.
Pelletization – Final HIPS pellets for molding/extrusion.