The temperature control during the granulation stage is critical to ensuring product uniformity in PVC processing. Here’s how it impacts consistency:
Material Plasticization and Homogeneity
Precise temperature regulation (typically 150–185°C for rigid PVC) ensures complete melting and uniform dispersion of additives like stabilizers and lubricants. Inadequate heating leads to partial plasticization, causing uneven particle size and internal stress, while excessive temperatures risk thermal degradation, forming bubbles or discoloration.
Melt Flow Stability
Temperature gradients across the extruder barrel (e.g., feed zone at 170–180°C, compression zone at 180–190°C, and die zone at 190–210°C) must be optimized to maintain consistent melt viscosity. Fluctuations disrupt flow patterns, resulting in uneven granule density and surface defects.
Avoidance of Thermal Decomposition
PVC is thermally sensitive; temperatures exceeding 200°C accelerate HCl release and polymer chain scission. Controlled cooling (e.g., gradual water baths at 20–40°C) minimizes residual stress and prevents delamination or brittleness.
Impact of Shear and Friction Heat
Screw speed and backpressure adjustments (40–60 rpm, 0.5–1.5 MPa) balance mechanical shear-induced heat generation. Poor control causes localized overheating, leading to heterogeneous particle morphology.
Post-Granulation Cooling
Rapid cooling after cutting (via controlled water baths or air systems) ensures uniform crystallization. Inconsistent cooling rates create internal voids or surface cracks, compromising mechanical integrity.
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