Automotive glazing and lighting — headlamp lenses, panoramic roofs, light guides — is a major outlet, as are electronics and appliance housings, mostly as PC/ABS blends. Safety and security glazing covers machine guards, riot shields, skylights and multiwall sheet. Medical devices use it for dialysers, oxygenators and connectors because it tolerates sterilisation. Optical applications exploit its refractive index for lenses and LED optics, and glass-filled and flame-retardant grades serve structural and electrical enclosure work.

Its toughness comes from the backbone being able to move locally under load — the carbonate linkage and the phenyl rings can rotate and absorb energy, so the material yields and draws rather than snapping. That mechanism needs a certain volume of material around the stressed point to work. A sharp notch concentrates stress into a region too small for yielding to develop, so the crack propagates before the polymer can respond, and the failure is brittle at a small fraction of the unnotched strength. The design rule that follows is simple and non-negotiable: generous internal radii everywhere, and no sharp corners, even cosmetic ones.

Because the carbonate linkage hydrolyses in the melt. Polycarbonate absorbs moisture from the air, and at 300 °C that water cleaves the chain, dropping molecular weight and, with it, the impact strength that is usually the reason for choosing the material. The moulding will look acceptable — perhaps with some splay or streaking — and will fail in service at loads it should have survived. The requirement is below 0.02% moisture, typically three to four hours at 120 °C in a desiccant dryer at −20 °C dew point or better.

More than most people expect, and the mechanism matters. Alkalis and amines hydrolyse the carbonate linkage directly. Ketones, esters, chlorinated solvents and many aromatic hydrocarbons swell and dissolve it. Beyond outright attack, polycarbonate is highly susceptible to environmental stress cracking, where a chemical that appears harmless on an unstressed sample causes rapid crazing on a part under load or with moulded-in stress. Proprietary products are the usual culprits in the field — cleaning agents, thread-locking compounds, mould releases, label adhesives, sunscreen and insect repellent have all caused failures. Every auxiliary chemical should be tested on a stressed sample before it is allowed near the part.

It depends entirely on the application. Polycarbonate is polymerised from bisphenol-A, which is classified in the EU as a reproductive toxicant and listed as a REACH SVHC, and trace BPA can be released from the polymer under hydrolytic conditions. Polycarbonate infant feeding bottles have been prohibited in the EU since 2011, and Regulation (EU) 2024/3190 restricts BPA in food contact materials generally, with staged transition periods. Automotive, electrical, medical device, glazing and industrial uses — which are the bulk of polycarbonate demand — are not affected. Food and drink contact applications need the current destination-market position confirmed before specifying, because this area has moved repeatedly and continues to.

Every shipment includes the grade technical data sheet, a Certificate of Analysis against the grade specification covering melt volume rate, density, mechanical properties and, for optical grades, transmission, haze and yellowness index; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; UL listings and flammability classification where applicable; destination-market regulatory confirmation for any food-contact application; an origin certificate; and further certificates where required.