Therefore, the first priority in any PVC processing is to inhibit thermal decomposition, and the core mission of stabilizers is precisely "thermal stability."

Compared to pipes and profiles, the extrusion process of PVC sheets presents a more severe challenge to thermal stability due to: longer material residence time, meaning the PVC melt endures high-temperature thermal stress for a longer period, dramatically increasing the risk of decomposition.

A higher risk of localized overheating; if the formulation or process is inappropriate, these "hot spots" can become the starting points for decomposition, spreading rapidly and forming persistent "yellow lines" or "black spots" on the sheet. Strict requirements for color and appearance, coupled with insufficient thermal stability, are the primary causes of initial yellowing. Any premature coloring (initial yellowing) renders the product unusable.

Furthermore, to reduce costs, a certain proportion of recycled scrap material is often added during board production. Recycled material has already undergone one heat treatment, partially depleting its thermal stability system, resulting in even worse thermal stability.

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