Certain engineering plastics are glass-filled, meaning glass fibres have been incorporated into the polymer to improve certain mechanical and dimensional properties. This is often referred to as ‘glass-filled’, ‘glass-fibre-reinforced’, ‘glass-reinforced plastic’ or simply ‘GF’.
Adding glass fibres has significant benefits including increased stiffness, strength, dimensional stability, and resistance to deformation. However, engineers should be aware that it can alter how the materials behave, processes, wears, and responds to impact.
Understanding these changes is essential when deciding if your project will require glass fibre reinforced components.
What is a Glass-Filled Component?
A glass-filled plastic is a composite material consisting primarily of a polymer resin reinforced with glass fibres.
The polymer forms the continuous matrix, while the glass fibres act as reinforcement. Together, they can produce properties that neither material would provide on its own.
Our range of glass-filled products:
- Polyether Ether Ketone GF30 (PEEK GF30)
- RENY (MXD6 GF50)
- Polyamide GF60 (PA66 GF60)
The number refers to the percentage of glass-fibre content by weight. Common grades include: 10%, 20%, 30%, 40% or even higher (such as we stock).
Why Add Glass Fibres to Polymers?
Unreinforced engineering plastics offer benefits such as low weight, corrosion and chemical resistance, and electrical insulation compared to traditional metal fasteners. However, their stiffness and deformation under sustained loads at elevated temperatures are limited in comparison to metallic products. Adding glass fibres can improve these characteristics.
The result is a material that retains many advantages of plastic while offering greater structural performance.
1. Increased Stiffness
One of the most significant effects of glass reinforcement is an increase in stiffness, commonly represented by the material's elastic or flexural modulus.
Glass fibres are considerably stiffer than the polymer surrounding them. When incorporated into the material, they help resist deformation under load.
2. Improved Strength
Glass reinforcement can also increase tensile and flexural strength, depending on the polymer, fibre content, processing conditions, and fibre orientation.
The glass fibres help carry loads through the polymer matrix, allowing the composite to withstand greater stresses.
This makes glass-filled grades attractive for applications where an unreinforced plastic might deform or fail under mechanical loading.
However, higher strength does not mean the material behaves like metal. The design still needs to account for the specific mechanical properties and failure modes of the reinforced polymer.
3. Better Dimensional Stability
Plastics can change dimensions due to temperature, moisture absorption, and mechanical loading.
Glass reinforcement can reduce some of these dimensional changes.
In many materials, adding glass fibres lowers the coefficient of thermal expansion (CTE) compared with the unfilled polymer. This means the component may expand and contract less as temperatures change.
For precision components, this improved dimensional stability can be extremely valuable.
Nylon provides a particularly useful example. Because nylon can absorb moisture, its dimensions and mechanical properties can change depending on environmental conditions. Glass reinforcement can improve dimensional stability, although it does not eliminate moisture absorption.
4. Improved Creep Resistance
Creep is the gradual deformation of a material subjected to a sustained load.
It is an important consideration in plastic components because polymers can continue to deform over time even when the applied load remains below their short-term strength limit.
Glass fibres help resist this deformation.
5. Improved Performance at Elevated Temperatures
As temperature increases, many plastics become less stiff and more susceptible to deformation.
Glass reinforcement can help the material retain stiffness and dimensional stability at elevated temperatures.
This does not necessarily mean that adding glass fibres dramatically increases every temperature limit of the base polymer. Instead, the reinforcement can help the material maintain useful mechanical properties as temperature rises.
For high-temperature applications, designers should still consider the polymer's continuous-use temperature, heat-deflection behaviour, creep performance, and environmental conditions.
Final Thoughts
The reinforcement can provide significant improvements in stiffness, strength, creep resistance, dimensional stability, and performance under elevated temperatures. These advantages make glass-filled plastics valuable for demanding structural components and fasteners.
But reinforcement also introduces trade-offs. Glass-filled materials can be more abrasive, more anisotropic, heavier, and sometimes less suitable for applications requiring flexibility or particular impact characteristics.
When deciding whether your project requires regular or glass-filled polymer components, understanding the benefits and trade-offs is key.