Polypropylene Hook

These ghost-like, translucent hooks are made from polypropylene. Invented in the 1950s, polypropylene is now the world's second most widely-produced synthetic plastic, after polyethylene. It is a thermoplastic polymer, meaning it can be heated and formed into different products by extrusion, injection moulding, blow moulding and spinning – as well as recycled. Polypropylene is strong, lightweight and tough, properties which make it suitable for weight-bearing applications like these hooks.

Polypropylene has good chemical resistance, a property which arises from its ‘low surface energy’. This makes it difficult for glues and other adhesives to ‘wet’ or bond to polypropylene surfaces. Successful glues for polypropylene are themselves made from or based on polypropylene. Alternatively, polypropylene can be joined by surface melting, a bit like the welding or soldering of metals. Its resistance to hand grease and repeated handling saw polypropylene become the material of choice for durable polymer banknotes, first introduced in Australia in 1988. Polypropylene bank notes are regarded as higher security than their paper-based predecessors thanks to their ability to incorporate security features such as transparent sections and special inks.

Elsewhere, polypropylene is used extensively in medicine to make items such as syringes, pipettes, sutures, surgical trays and specimen bottles because it can withstand the heat of an autoclave, meaning it can be sterilised. Implantable polypropylene devices, such as surgical mesh to treat hernias or pelvic organ prolapse, have attracted controversy for their associated complications. In 2020, the COVID-19 pandemic saw demand for polypropylene spike, thanks to its use to make meltblown fabric, a synthetic textile used for making medical-grade facemasks.

In the home, polypropylene is used in a wide variety of familiar applications, for example food containers, on account of its resistance to fats and chemicals, as well as its strength and low toxicity. It is resistant to fatigue so can be bent many times without breaking, making it a good material for in-built hinges, such as those on flip-top bottles or the lids of Tic Tac boxes.