In this post we break down the best adhesives which can be used to reliably and efficiently bond Polystyrene; alongside a general explanation of the different forms of Polystyrene.
Polystyrene (PS) is one of the most commonly used thermoplastics in the world. It is a cheap resin per unit weight which can be easily moulded into sheets, foams and films, and is therefore used extensively in protective packaging applications. Naturally, Polystyrene is a clear, hard and brittle material. PS is also an excellent electrical insulator with superb optical clarity due to its lack of crystallinity. PS can be easily processed to give various variations of it, each fit for a different purpose, which are used and sold commercially. A few of these are listed and described in the section below.
The three most significant grades of Polystyrene are:
XPS (Extruded Polystyrene, also known as Styrofoam™)
Styrofoam™ is an extremely lightweight, shock-absorbing thermoplastic that is a solid foam at room temperature. XPS possesses these qualities partly from being 90% made up of air. While in a liquid state at its melting point, the material becomes extremely malleable, allowing it to be formed into various shapes and moulds. It is also an excellent insulator, making it ideal as packing and craft material. The name Styrofoam™ is typically, but inaccurately, used to also refer to EPS, which is Expanded Polystyrene, a tough and rigid foam which is an alternative to XPS. EPS is similarly used for insulation purposes in walls, roofs and foundations.
GPPS (General Purpose Polystyrene)
GPPS is a fully transparent (“crystal-clear”), rigid and odourless solid product. Commonly, refrigerator trays and boxes are made from GPPS, as well as audio cassette and CD cases. However, it can also be manufactured in the form of 2-5mm pellets. It has a good resistance to heat and excellent resistant to many oils and corrosive chemicals.
HIPS (High Impact Polystyrene)
HIPS typically contains 5-10% rubber and as a result has a high marginal resistance to tearing and impact, as well as being durable. Sheets and rolls of HIPS are easily manufactured for use in printing and forming applications. They are especially suitable for lithographic or flexographic printing of displays, in addition to food and medical packaging, due to being in compliance with their regulations.
Main Properties of Polystyrene
- Surface energy: 41 mJ/m2
- Maximum service temperature: 65°C
- Softening temperature: 107°C
Adhesives Used to Bond Polystyrene
Permabond 940 is a low-odour, non-frosting and non-fogging cyanoacrylate adhesive which can be easily applied to Polystyrene to provide reliable bonds. It provides a good aesthetic appearance due to being non-frosting, and also improves worker comfort due to being low-odour. The 940 is very stable and will provide the best performance for one year when refrigerated.
Permabond UV630 and Permabond UV640 are fast setting, single part UV curable adhesives which give resilient and high shear-strength bonds especially for plastics. They have outstanding elongation (> 110%) and impact resistance, making them ideal for applications involving substrates with different coefficients of thermal expansion. They are easy to use and can be cured with the use of low-power lamps.
Surface Preparation & Processing Tips required to Bond Polystyrene
To achieve a strong bond to Polystyrene, ensure that the surfaces are clean, grease-free and dry before applying your choice of adhesive. We recommend using a mild solvent such as the Wipemaster Wipe 9 to clean the surfaces, as stronger solvents such as acetone can attack and damage the polystyrene bonds.
As Polystyrene is vulnerable to stress cracking over time, you can minimize the chances of it happening by ensuring that you avoid applying too much of the adhesive on the surfaces, and that the dwell time of the adhesive is kept to a short length. For similar reasons, when designing a joint to be bonded, avoid over inserting one piece into another by putting a stop into the joint to prevent chances of stress cracking.