To char or not to char?

摘要

As reported elsewhere in this special issue, fire retardants represent-by quite some margin-the biggest sector within PL) additives. And with good reason: fire is fundamental (if not elemental, in our post alchemical era), one of the biggest threats to human life outside natural death, disease, homicide and drug overdose. Every year some 150,000 people are killed by fire (and seven million receive serious injuries from burns). One of the most successful flame retardants comes from fire itself: char. The Japanese technique of Yakisugi (sometimes known as 'shou sugi ban') has been used for over 300 years to protect wood from weather, insect infestation, and fire. Similar processes have also been used for generations in other cultures: as evident in the timber chalets seen in the Swiss Alps. Charring is the chemical process of incomplete combustion of materials exposed to high heat. The heat removes oxygen and hydrogen (plus water vapour and VOCs) from the material, leaving a char principally composed of carbon. The char is evident from its black colour, literally 'carbon black'. Whereas ash that results from complete combustion presents a grey or whitish colour.