High Impact Polystyrene (HIPS) is a versatile and cost-effective thermoplastic material. It is a modified version of standard polystyrene, offering a significant increase in durability and resilience compared to its brittle predecessor. Its ease of processing and low material cost have established HIPS as a popular choice across various industries.
The Composition That Creates High Impact Resistance
The distinction between standard polystyrene (GPPS) and HIPS lies in the inclusion of a rubber component, typically polybutadiene. This modification is achieved by dissolving the polybutadiene rubber into styrene monomer before polymerization. Through graft copolymerization, chains of polystyrene chemically bond to the polybutadiene backbone.
This process results in a two-phase structure where tiny, dispersed rubber particles are embedded within the rigid polystyrene matrix. The rubber phase absorbs and dissipates energy when the material is subjected to impact. Instead of a crack propagating straight through, the rubber particles initiate localized stress whitening and internal voiding, which effectively halts the fracture. This unique internal morphology is responsible for HIPS’s enhanced toughness and superior impact strength.
Essential Characteristics of HIPS
The modified composition grants HIPS a combination of physical properties suitable for mass production. It possesses a significantly higher impact strength compared to General Purpose Polystyrene, making it far less prone to shattering or fracturing under stress. Despite this improved toughness, the material retains excellent rigidity and dimensional stability. Molded or formed parts consistently maintain their shape and precise dimensions over time, resisting warping or shrinking.
HIPS offers excellent processability using common manufacturing methods. It is particularly well-suited for both injection molding and extrusion, and it is a preferred material for thermoforming, such as vacuum forming. The material heats quickly and becomes highly pliable, allowing for intricate designs and consistent forming behavior. Furthermore, HIPS offers a smooth surface quality that readily accepts inks, adhesives, and paint, which is useful for signs and printed graphics.
Everyday Uses of High Impact Polystyrene
HIPS is often chosen where a balance of performance and affordability is required. One of its most recognized applications is in the internal components of household appliances, particularly the inner liners and door shelves of refrigerators. The material’s dimensional stability and toughness allow it to withstand the constant temperature changes and minor impacts that occur in these environments.
In the electronics sector, HIPS is frequently used for housing and casings for devices. Examples include the shells of computer monitors, printer bodies, and certain electrical insulation components. Its stiffness and ease of molding make it a practical choice for creating the custom shapes required for consumer electronics.
Beyond durable goods, HIPS is a staple in the packaging industry. It forms many disposable food containers, such as clamshells, yogurt cups, and salad bowls, due to its hygienic properties and capacity for moisture resistance. Manufacturers also rely on HIPS for creating point-of-purchase (POP) displays, promotional signs, and temporary fixtures in retail environments. Its ability to be easily printed upon and die-cut allows for flexible and cost-effective marketing materials.
Handling HIPS Waste
HIPS is technically a recyclable material, identified by the Resin Identification Code (RIC) #6, the same designation used for all other forms of polystyrene. The recycling process involves collecting, cleaning, shredding, and then melting the plastic to mold it into new products.
Despite being recyclable, its acceptance in municipal collection programs is highly variable across different regions. Many local authorities do not accept plastics bearing the #6 code due to sorting challenges and the contamination risks associated with mixed plastic streams. Consumers should check local guidelines to determine if HIPS items, such as food trays or electronic casings, can be placed in their curbside bins. The recycled material can be repurposed for lower-grade applications like coat hangers, flowerpots, and certain packaging materials.