Monday 26 October 2020

Rule of Thumb for Plastic Part Design: Increase HDT & Modulus With Fillers

In this blog post, I present to you another helpful rule of thumb for plastics part design and material selection. 

It is well researched that fillers such as glass fibers can increase thermal and mechanical properties of amorphous and semi-crystalline thermoplastics. 

For example [1], unreinforced polyamide 6 has a glass transition temperature of 65°C with a heat deflection temperature (HDT) of 65°C at 1.82 MPa. The modulus declines from 2.81 GPa (pre- Tg) to 0.56 GPa (post-Tg). This is a decrease of 80%. 

Adding 14% glass fiber as reinforcements increases the HDT from 65°C to 200°C at 1.82 MPa. Modulus is almost doubled and the decline from pre- to post-Tg is 55% (from 4.46 GPa to 1.98 GPa).

Finally, with 33% glass fiber reinforcements, HDT can be slightly increased to 210°C at 1.82 MPa. However, modulus can be increased to 7.87 GPa and the decline is now below 50% (from 7.87 GPa to 3.99 GPa). 

Allover, the Tg changes only in few degrees (from 65°C with the base resin to 70°C with 33% glass reinforcement). 

Important is to keep in mind that HDT is a single point value and often used as a maximal use temperature. Therefore, it is always good to look at the storage modulus curve (as shown in the graph in the beginning) which covers a wide temperature range. This allows you to decide if the selected material is suitable to fulfill the application requirements. Other factors such as molecular weight increase the mechanical properties too. 

Thank you for reading and #findoutaboutplastics

Herwig Juster

More Rule of Thumbs here: 


[1] M. P. Sepe – Dynmaic Mechanical Analysis for Plastics Engineering


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