Advances in fibreglass reinforcements for thermoplastics have evolved from conventional chopped strand to long-glass fibres to hybrids of long glass and carbon fibres.

A key aim is lightweight while maintaining or enhancing mechanical properties. Key challenges are warpage reduction and ease of processing. Fibreglass products with a flat rather than round cross-section may address these issues while offering new benefits.

A new type of flat fibreglass is said to facilitate higher fibre loadings, and better mechanical properties, including higher impact strength in injection moulded thermoplastic composites, while also reducing warpage in thin wall sections.

Also, the flat glass reportedly enhances thermoplastic processing by providing better fluidity (increased spiral flow), reducing friction, and lowering fibre entanglement and breakage.

The flat fibres reportedly tend to flow in planar sheets like mica rather than rolling and tumbling like conventional round glass filaments.

In turn, this can help provide for a more isotropic dispersion and also allows a higher fibre-volume fraction to be achieved because the fibres pack more closely, as confirmed by scanning-electron micrograph images.

The flat glass products also help thwart warpage (differential shrinkage and residual stress relaxation) of a plastic or composite part after de-moulding.

Warpage tends to be a function of non-uniform shrinkage between flow and cross-flow directions of a part, which is particularly exacerbated in high-pressure processes like injection moulding.

This effect is greater when more fibres line up in the direction of polymer flow than in the cross-flow direction, leading to higher shrinkage and warpage in the cross-flow direction.

Flat fibreglass helps reduce warpage significantly in thin-wall parts because its flow properties differ from those of standard round glass.

In the case of thin-wall parts, the cross-flow (through-thickness) direction represents a smaller proportion of the total thickness versus skins aligned with resin flow, so the effects of non-uniform shrinkage are more pronounced.

To some extent, design and gate placements can help reduce warpage, as can process changes such as lowering speeds of fill and/or packing pressures.

However, the innovative flat glass helps reduce warpage significantly without any other changes, simply by how the reinforcement fills parts and how it behaves in conjunction with the resin matrix. Moreover, it helps reduce moulding pressures and enables the same part to be moulded on smaller injection presses with fewer gates.

Glass-filled semi-crystalline resins using this flat fibre have been moulded as thin as 1 mm (0.04 in.) without warpage.

The flat fibres are said to exhibit excellent bonding and mechanical properties and are recommended for applications in the automotive and electrical/electronic industries.

In all other properties, the flat strands are said to be equivalent to conventional round glass fibre of the same type at the same loading.

The new glass comes from Chongqing Polycomp International Corp. (CPIC), Amsterdam, N.Y., Headquartered in Dadukou, China, a subsidiary of YTH Group, claims to have the answers.

CPIC is a global conglomerate of fibreglass, mineral, composites, textiles, financing and trading companies, and reportedly the world’s third-largest fibreglass manufacturer by installed capacity.

Source: ptonline.com

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