The use of adhesives and fixings — AQA A-Level Design and Technology: Product Design
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The use of adhesives and fixings explained
Solvent cements such as Tensol or acrylic cement bond thermoplastics by softening the surfaces: the solvent dissolves a thin layer of each part, the softened polymer chains intermingle, and as the solvent evaporates the joint reforms as a continuous welded bond.
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They are not gap-filling glues; parts must fit closely, and the joint is usually held under light pressure while solvent evaporates. They work on thermoplastics such as acrylic (PMMA) but not on thermosets, which cannot be re-softened. Learners should connect the material class to the method: solvent welding gives strong, near-invisible joints on acrylic, but needs good ventilation because of solvent vapour and careful alignment because the bond forms quickly.
Your focus
- Describe how solvent cements such as Tensol or acrylic cement weld thermoplastics.
- Explain why solvent cements suit thermoplastics such as acrylic but not thermosets.
- Identify practical requirements such as close fit, light pressure and ventilation.
The use of adhesives and fixings exam tips
Marking Points
- Identifies that solvent cements such as Tensol or acrylic cement bond thermoplastics by softening the surfaces with a solvent.
- Explains that dissolved polymer chains intermingle and, as solvent evaporates, reform as a continuous welded joint.
- States that the method suits thermoplastics such as acrylic (PMMA) but not thermosets, which cannot be re-softened.
- Recognises that parts need a close fit and light pressure, as the cement is not a gap-filling adhesive.
- Notes practical considerations such as ventilation for solvent vapour and careful alignment because the bond forms quickly.
Examiner Tips
- 💡Explain the welding mechanism (soften, intermingle, evaporate) rather than just naming the cement.
- 💡Link the cement to a named thermoplastic such as acrylic to show material knowledge.
- 💡Include one practical consideration, such as ventilation or close fit, to demonstrate applied understanding.
Common Mistakes
- Treating solvent cement as an ordinary gap-filling glue: correction — it works by softening and welding the plastic, so parts need a close fit.
- Assuming it bonds any material including thermosets: correction — it only works on thermoplastics that can be re-softened by the solvent.
- Ignoring safety: correction — solvent vapour requires good ventilation during use.