Filled PP Compounds: Talc, Calcium Carbonate and Glass Fibre Explained

Much of the PP used in appliances, automotive parts and furniture is not plain polymer. It is a compound: PP blended with a mineral filler or reinforcement to change stiffness, shrinkage, heat resistance or cost. Recycled PP compounds are widely available, and many are made from recycled PP with fresh filler added. Understanding what each filler does helps you choose the right grade and check what you receive.

This guide covers the three common types: talc, calcium carbonate and glass fibre.

What fillers and reinforcements do

A filler is a material added to a polymer to change its properties or lower its cost. In PP the main effects are:

• Higher stiffness: parts flex less under load.
• Lower and more even shrinkage: better dimensional stability and less warping.
• Better heat resistance: the part holds its shape at higher temperatures.
• Higher density: each kg of compound makes fewer parts than unfilled PP.
• Often lower impact strength: especially at low temperatures.

For an overview of compounds, see compound and PP filled and reinforced compound.

Talc-filled PP

Talc is a plate-like mineral that increases stiffness and improves dimensional stability well. Talc-filled PP is widely used for automotive interior parts, appliance housings and components that need to stay flat and rigid. It can also improve heat resistance.

Talc grades are named by their filler content, for example "T20" or "T40" for nominally 20 or 40 percent talc. These names are a trade convention, so confirm the actual content by ash test rather than relying on the label.

Calcium carbonate-filled PP

Calcium carbonate is cheaper than talc and is mainly used to reduce cost and add some stiffness. It is common in household goods, furniture, raffia and general moulded items. It improves stiffness less than talc at the same loading, but it is widely available and easy to process.

Because calcium carbonate is sometimes added to recycled material without being declared, buyers should check ash content even on grades sold as unfilled. Our post on black recycled granules covers how filler can hide in dark material.

Glass fibre-reinforced PP

Glass fibre is a reinforcement rather than a simple filler. It raises stiffness, strength and heat resistance much more than mineral fillers, which is why glass-filled PP is used for structural automotive parts, fan blades, appliance frames and parts under load.

• Fibre length matters. Each time glass-filled PP is ground and reprocessed, fibres break and properties drop. Recycled glass-filled PP may not perform like the original.
• Glass fibre causes wear on screws, barrels and moulds.
• Glass-filled parts can show fibre on the surface and may warp differently along and across the flow direction.

For automotive parts, follow the customer's material specification and approval process. See recycled plastic for automotive and appliances for more.

Checking filler content: density and ash

Two simple tests tell you most of what you need:

Test	What it tells you
Ash content	The share of mineral or glass that remains after the polymer is burnt off. This is the most direct measure of filler content.
Density	Unfilled PP is about 0.90 to 0.91 g/cm3. Filled PP is denser, and density rises with filler content.

Ask for ash and density on every lot, and agree a target and tolerance with your supplier. Ash does not tell you which filler is present; if that matters, ask for the filler type in writing or have a lab identify it. MFI is still useful, tested at 230 C with 2.16 kg, but filled grades usually flow differently from unfilled ones with similar base polymer.

Impact strength trade-offs

Fillers usually lower impact strength, especially in the cold. Compounders offset this by using impact-modified PP copolymer as the base or adding elastomers. If your part must survive drops, clips or knocks, ask for impact test data, run your own drop or snap tests in trials, and do not judge the grade on stiffness alone.

Sourcing filled PP compounds

When you post a requirement, include the filler type and nominal content, base polymer if known, colour, ash and density targets, MFI, any impact requirement, the part you make and monthly quantity. PlasticSetu's sourcing desk collects quotations from verified suppliers, arranges samples for trials and tracks dispatch. Get quotes to start.