Polypropylene Sheet, Perforated

Perforated polypropylene sheet in natural, sold by the full sheet.

Perforated polypropylene sheet, 1/4 inch diameter holes on 1/2 inch straight-line centers - a square pattern, not staggered - giving 19.6 percent open area. It is among the most flexible of the perforated plastics, and it carries polypropylene's chemical resistance into applications where a metal screen would corrode.

Weight is figured on the perforated sheet, not the blank: the holes remove 19.6 percent of the material, so you are not paying freight on metal that is not there.

It suits filtration and separation media, drainage and dewatering panels, tank baffles and distributor plates, parts-washer and degreaser basket and tray liners, plating-line racks and drip trays, ventilation and diffuser panels, and guarding in wet or corrosive areas.

Polypropylene is the workhorse of chemical-resistant fabrication: the lightest of the common engineering plastics at a specific gravity of 0.905, it floats, it welds, it shrugs off acids and alkalis that attack most other thermoplastics, and it costs a fraction of what the fluoropolymers do. Tanks, ducting, wash-down fixtures, laboratory furniture and food-processing parts are all built from it.

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.

On temperature, read the load with the number. Continuous service runs 180 to 212F depending on grade. Heat deflection is 210F at 66 psi; at 264 psi the published figures disagree badly across mills, so treat anything above about 190F under real load as something to test. And the number that catches people out: homopolymer has lost about 92 percent of its room-temperature tensile strength by 150F. Polypropylene melts around 320F, but that is not a service temperature and nothing here should be designed near it.

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.