The unprecedented characteristics and shock-absorbing properties of Polystyrene (EPS & XPS)

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Polystyrene propertiesThe Unparalleled properties of polystyrene make it one of the most versatile and widely used polymers. Polystyrene properties combined with its highly economical nature make it possible for manufacturers to come with innovative products. The distinctive characteristics of polystyrene give it a wide range of end-use applications. One such exceptional property displayed by polystyrene foam is shock absorption. PS foams are widely used as shock absorbers in packages, helmets, automotive, etc. Before analyzing styrene properties or polystyrene properties, let us understand the significance of shock absorbers.

 

Need for shock absorbers

Whenever a device or a human, for that matter, is subjected to a sudden vibration or shock impulse, there is a definite possibility of injury or mechanical fracture, or damage. While vibration is repetitive, shock is a single-time event. A shock is generated by dropping down or by collision, or by hitting a bump. In all these cases, the internal component would face the full impact. To avoid such damages and to mitigate the loss due to damage, a shock absorber becomes vital. A shock absorber is generally used to absorb and damp shock impulses. Lightweight, high-performance foams are the best shock absorbers as they can isolate and absorb sudden vibrations.

Different types of polymers used in making shock-absorbing materials are polystyrene, polyurethane, polypropylene, and polyethylene. There are open-cell foam and closed-cell foam. While open-cell foams allow liquids and gases to pass through them, closed-cell foams exhibit high resistance.

Polystyrene as a shock-absorbing material

Polystyrene foams are 95-98% air and 5-2% Polystyrene. Polystyrene foams are cost-effective in production and raw material, and there are many expanded polystyrene suppliers and manufacturers in UAE. The general polystyrene properties like low density, rigidity, favorable cushioning properties, easy processing and mouldability, high compression strength, high impact strength make it an ideal shock-absorbing material. Polystyrene foams are cost-effective. The shock-absorbing levels are estimated mainly by studying load-deflection curves via a ball drop test, viscoelastic behavior of the polymer, density of the material, and load-bearing strength.

A shock-absorbing material proves to be effective if it can absorb and dissipate the impact energy and withstand the effects of compression and repeated use.

Types of Polystyrene foams

Polystyrene foams are of 2 types: Expanded polystyrene and Extruded Polystyrene.

Expanded Polystyrene foams(EPS)

Manufacturing Process

Polystyrene synthesized by suspension polymerization of styrene monomer is then impregnated with a blowing agent, usually pentane, to produce expanded polystyrene. It’s a closed-cell, white foam with an average density of 11 to 32 kg/m3.

Properties

  • Rigid and tough
  • Lightweight
  • Low moisture absorption
  • Excellent cushioning properties
  • Maximum operating temperature is around 80 °C
  • High compressive strength
  • Excellent dimensional stability

Extruded Polystyrene foams(XPS)

Manufacturing Process

XPS has a different manufacturing process. After adding blowing agents and additives to polystyrene, it is extruded into sheets in a continuous extrusion process. It is also a closed-cell rigid foam like EPS. The trademark Styrofoam is used for “extruded closed-cell” polystyrene foams made by Dow Chemicals. The other lesser-known brand names for XPS foam include “GreenGuard” and “Foamular.”

Properties

  • Rigid and tougher
  • Lightweight
  • Low thermal conductivity
  • Very low moisture absorption
  • More resistant to water vapor than EPS
  • Higher compressive strength than EPS
  • Improved surface roughness

Why are PS foams ideal Shock absorbing materials?

Packaged products are usually transported longer distances. The products will be subjected to multiple shocks and impacts during transit. The high compressive strength, rigidity, and highly lightweight property make EPS foams ideal for packaging as they protect the product from multiple shocks and impacts and make transportation easier.

Interesting results are obtained when EPS or XPS foams are subjected to mechanical tests to study their compression behavior. The closed-cell foams initially exhibit a linear elastic behavior which means stress is proportional to strain. Beyond the threshold point, it produces a large plateau before the collapse of the cell. This large plateau region gives these polystyrene foams the energy-absorption capacity they need. A material’s elastic modulus depends on the density; the elastic modulus and the plateau stress increase with increasing density. The energy absorption increases with higher plateau stress for a given strain meaning these foams exhibit moderate strain rate dependency. The increasing strain rate does not affect the compression behavior or shock absorption capability of the foam. Even with different loading rates, the behavior of the foams is not altered much, which makes them ideal for repeated use.

The shock absorption property is also dependent on the thickness of the foam. With minimum thickness, these materials provide superior cushioning to the internal products and protect them from damages. These foams’ excellent dimensional stability and high shock absorption capacity help them retain their shape after a heavy impact. Given the high compressive strength, the packages made out of XPS foams can be stacked one over the other without any problem. With easy mouldability, they show outstanding design flexibility and prove a perfect solution for bespoke packaging. Also, the low production cost and low raw material cost make it highly economical.

Foams are used as sandwich structures in many applications in automotive. Helmets have shock absorption liners made out of EPS foams as they exhibit the ideal shock absorption property required for usage in helmets. There is no way to generate or destroy energy. PS foams rightly absorb and channelize the impact energy, thereby avoiding a head injury. EPS foams are reliable and highly durable as their properties don’t change in the long run. PS foams perform energy management so perfectly that they find applications in helmets and other protective products like car seats, sports pads, etc.

To summarize, PS foams possess exceptional properties, and the shock-absorbing property of EPS and XPS gives them a wide range of applications requiring protective functions.

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