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Polymethyl methacrylate (PMMA)
3-8 usd/kg
Polymethyl methacrylate (PMMA), acrylic, is a transparent plastic often compared to glass. Indeed, the two materials are used in many of the same applications – glazing, aquariums, household items, tableware and furniture, for example – with acrylic being lighter, more resistant to impact and easier to form into complex and intricate shapes. The disadvantages of acrylic, when compared to glass is that it is not inert (glass is virtually inert) and will crack and weaken if exposed to certain chemicals, it softens and melts at much lower temperatures (160 degC versus 1,700 degC for glass), and it is less scratch resistant.
As a transparent plastic, it is available in standard and custom colours, from muted tones through saturated fluorescents. Edge glow is the result of light passing through the surface and refracting internally until it meets a cut edge in tinted or semi-transparent materials. This phenomenon is utilised in signage, lighting and instrument panels, for example, that are made from acrylic. A cut edge may be the perimeter, or a score on the surface, such as made by laser cutting or engraving.
Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products
Low circularity potential
Microplastics
Acrylic adhesives are tailorable to a wide range of applications. They form cross-links in a one-way reaction, which sets them apart from moulding and casting acrylic resins. They typically have very good resistance to chemicals and weathering, high bond strength to a range of plastics and metals, good toughness for structural applications (rubber-toughened systems), or high rigidity, and come in a range of colours from transparent to opaque. They are used in automotive (structural applications in place of traditional mechanical fasteners) aerospace, furniture, consumer goods, sports equipment, construction (bonding and sealing windows, for example) and even medical implants. Care must be taken with these products, due to risk of strong odour, flammability and an upper service temperature of 120 degC (although grades have been developed that can tolerate 200 degC).
Similar to epoxy adhesive, they come in two parts, which are mixed together to initiate the cure. They range from low viscosity (high flow and wet-out) to paste-like (non-sagging). Compared to epoxy adhesives, acrylics can be used to bond to a wider range of surface finishes, with minimal or no surface preparations; strength build-up is much more rapid once handling time is over; and they can provide higher strength bonds between low surface energy (LSE) materials, such as polyethylene (PE), polypropylene (PP) and polytetrafluoroethylene (PTFE), without the need for exotic surface preparation. However, they should not be used with wood, rubber, or concrete – epoxy is more suited to these applications.