Today's KNOWLEDGE Share
Every process change has a thermodynamic story
Many people working in injection molding are skilled at identifying defects and knowing which adjustments can solve them.
One of the possible corrective actions is raising the melt temperature, but I always like to go one step deeper and ask what really happens thermodynamically inside the polymer when we do that? 🤓
In my recent troubleshooting case, it was polypropylene, and I increased the barrel temperature by 20°C.
When the temperature rises, the average kinetic energy of the molecules increases. This means the intermolecular forces (mainly van der Waals forces between the chains) are more easily overcome, allowing greater chain mobility. The viscosity drops exponentially with temperature which leads to easier flow through the mold cavity and better replication of fine details.
At the same time, the free volume between chains expands, enabling more molecular motion and reducing resistance to shear.
However, this also affects the crystallization kinetics: higher melt temperature delays the onset of crystallization, often resulting in lower overall crystallinity and potentially a slightly softer or less rigid part if cooling is not properly managed.
From a rheological point of view, this shift also changes the shear-thinning behavior of the melt- at higher temperatures, the slope of the viscosity vs. shear rate curve flattens, which means the material becomes less sensitive to variations in flow velocity.
Every adjustment we make in injection molding carries a thermodynamic and structural consequence — and understanding that connection transforms process tuning from a routine action into an informed decision.
That’s one of the reasons I love this field.
❇️ Because understanding polymer behavior means improving processes with purpose.
Image taken from: www.researchgate.net
source : Krstina Jankovic
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