Polypropylene Sheet, Heat Stabilized

Heat-stabilized polypropylene sheet in black and natural, sold by the full sheet.

This is the heat-stabilized grade, and it is a different purchase from plain polypropylene. Heat stabilization is what lets it take repeated steam autoclaving without the embrittlement that finishes off standard stock, which is why it is specified for reusable medical and laboratory parts rather than for tanks.

Published figures for grades of this type: long-term service to 212F and short-term to 284F, heat deflection 187F at 264 psi, tensile yield around 4,900 to 5,100 psi and flexural strength 6,500 to 7,800 psi. The slide and wear properties are good, and the material is autoclavable and tolerates cold sterilization.

What we will not claim for you. Biocompatibility and USP Class VI status vary by specific grade and color within this material family - one maker's white is tested to USP Class VI while another mill rates its standard homopolymer USP Class VI: no. If your part needs USP Class VI, ISO 10993 testing or a BSE/TSE statement, tell us and we will get the certificate for the specific sheet before you commit. Do not infer it from the fact that this is the medical-grade line.

It goes into autoclavable instrument trays and handles, provisional trial components, sterilization cases, and pharmaceutical and food-engineering parts.

Chemical resistance is the reason to buy it. Acids, bases, alcohols, detergents, lower ketones, aldehydes and water-soluble salt solutions are, in the resin producer's words, usually not regarded as antagonistic. Dilute to mid-concentration sulphuric is a documented working envelope - tanks are built in homopolymer for 10 to 40 percent sulphuric from 41 to 158F. Concentration is what decides it, not just the chemical: polypropylene handles 30 percent sulphuric but not concentrated, 10 percent nitric but not 40 percent. Oxidizing acids are where it fails.

What it is not for: chlorinated solvents, aliphatic and aromatic hydrocarbons, ketones and esters are unacceptable; hot water and steam are limited service; and bleach and hypochlorites cause a failure that looks like stress cracking but is actually oxidative attack. Polypropylene is largely outside the stress-crack failure mode that troubles polyethylene, which is worth knowing - but it is not immune to oxidizers, and at 120F the not-recommended list grows substantially.

Outdoor use, and this is the one that comes back as a warranty claim. Standard polypropylene is not UV stabilized. Continuous sunlight is rated limited, and exposure causes progressive loss of tensile strength and elongation - polypropylene's peak photochemical sensitivity sits at 370 nm, inside the UV-A band, which makes it the more vulnerable of the two common polyolefins. For outdoor or UV-exposed service, specify a UV-stabilized polypropylene grade or UV-stabilized HDPE. Color alone is not UV protection, black included: the UV-stabilized polypropylene grades actually sold are blue, beige, gray and white, and no mill we can find publishes a UV service claim for black polypropylene.

Joining is by welding, and every mill leads with it. Heated-tool butt welding, hot gas and extrusion welding are all rated excellent, with extrusion welding running 410 to 464F material temperature and 410 to 572F gas under DVS 2207-4. A good weld approaches base-material yield. Use matching polypropylene weld rod - the wrong rod is the one weld defect a supplier can actually prevent, so order it with the sheet.

It machines easily - about a 3 on a 1-to-10 scale - with sharp tools, high rake angles and good chip clearance. It is soft and it moves, so expect more spring-back than acetal or nylon and allow for the thermal expansion, which published sources put anywhere between 4.6 and 10.6 millionths per degree F. Hold thin parts gently; clamping marks stay.

Food contact: available in grades compliant with FDA 21 CFR 177.1520, olefin polymers. Compliance attaches to the specific resin and color formulation, not to polypropylene generically - and the regulation bounds density at 0.880 to 0.913, which some published sheet densities sit outside. Request the manufacturer's declaration of compliance for the product supplied if you need it on file.