Polypropylene (PP) Brush Filament: Properties and Uses

What polypropylene is

PP is a polyolefin made by polymerising propylene. Brush filament is usually homopolymer PP, which is stiffer and melts higher than the copolymer grades used for impact-resistant moulding. Because it contains no polar groups, PP is essentially inert to water and to most acids, alkalis and solvents. For food contact in the US, olefin polymers are covered by 21 CFR 177.1520.

Key properties with real numbers

PP's low density is a real cost advantage. Brushes are filled by volume, so a filament about 20 % lighter than nylon means about 20 % less filament by weight for the same brush. Its stiffness also stays the same wet or dry. The weak spots are heat, because it softens at much lower temperatures than nylon or PBT, and cold, because homopolymer PP can become brittle around or below freezing.

Where PP is used in brushes

• Road sweeper brooms: main brooms, gutter brooms and wafer sections, often mixed with flat steel wire.
• Floor scrubber disc brushes, where standard scrubbing fill is commonly about 0.5–0.6 mm PP.
• Fruit and vegetable washing rollers, cow brushes and other outdoor or wet brushes, usually UV-stabilised.
• Pile weather-stripping and low-cost strip brushes.

Pros and cons

• Pro: lowest density and lowest cost per brush of the common synthetics.
• Pro: effectively zero water absorption, so stiffness is the same wet or dry, and it floats.
• Pro: inert to most acids, alkalis, oils and solvents, and resists fungal growth.
• Con: melting point of 160–165 °C, so it softens with friction heat or hot water much sooner than nylon.
• Con: lower bend recovery than nylon, so bristles take a set and splay sooner under constant load.
• Con: homopolymer becomes brittle at around −10 to 0 °C, which matters for winter sweeping.
• Con: needs UV stabiliser for long outdoor life.

Diameters and cross-sections

PP filament is extruded in a wider range of sizes than most brush polymers. Stock round filament typically runs from about 0.15 mm to 1.5 mm, and sweeper fills go much thicker. Sweeper brooms on our list use 2.5 mm and 3 mm poly, while floor-scrubbing discs use about 0.5–0.6 mm. Flat, ribbed, X-shaped and hollow profiles are also common, because the flat faces and edges help pick up fine debris and add stiffness without much extra weight.

Because PP's modulus is less than half that of dry nylon, a PP brush usually needs a thicker filament, a shorter trim or a denser fill to match the stiffness of a nylon brush. Crimped PP spreads at the tips and gives a fuller face, while straight PP packs tighter and is used where a firmer, more uniform edge is wanted.

Heat resistance is the other sizing factor. One homopolymer fibre resin lists a heat deflection temperature of 105 °C. Friction heat at the tips of a fast-spinning gutter broom can soften fine PP filaments well before that. This is one reason road brooms combine PP with flat steel wire rather than relying on very thin poly.

How to specify PP filament

Give diameter (for example 0.5 mm for scrubbing or 2–3 mm for sweeper brooms), cross-section (round, flat or ribbed), crimped or straight, trim length, colour, and whether UV stabilisation is needed. For sweeper brooms add the machine model, outside and inside diameters and the bore or mounting pattern. Our gutter broom selection guide explains PP versus wire versus mixed fills.

If the brush will work in freezing conditions or near hot surfaces, mention it in the RFQ. The factory can then suggest a copolymer-modified filament, a mixed fill or a different polymer.

Alternatives to PP

For better recovery and heat resistance in wet service, step up to PBT or PA612. For dry industrial brushes needing stiffness, use PA66. For brooms, PET is a stiffer polyester alternative. For heavy compacted dirt on roads, PP is usually mixed with flat steel wire rather than replaced.

Frequently asked questions

Is polypropylene or nylon better for a scrub brush?

PP is cheaper, lighter and does not soften in water, which suits most floor and wash scrubbing. Nylon recovers better from bending and tolerates heat and abrasion better, so it lasts longer under heavy or hot duty.

What temperature can polypropylene bristles take?

Homopolymer PP melts at about 160–165 °C and softens at about 152 °C (Vicat). Practical brush service temperatures are far lower, so avoid PP for hot surfaces or hot washes.

Do PP sweeper brushes crack in cold weather?

They can. Homopolymer PP has a brittleness temperature of about −10 to 0 °C, so bristles can snap more easily in freezing conditions. Mention winter use when specifying.

Does polypropylene absorb water?

Essentially no. Producer data gives less than 0.01 % after 24 hours of immersion.

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