Polystyrene Sheet Pressing from Pellets (13 mm)

Overview

This article documents a validated process for pressing 13 mm thick GPPS polystyrene sheets from pellets using a heated sheet press with fully programmable temperature and pressure profiles.

The goal is a low-stress, bubble-free, warp-free plate, suitable as a baseline recipe for further optimization.

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Material Properties (GPPS)

• Density: ~1.05 g/cm³
• Glass transition (Tg): 95–100 °C
• Optimal processing window: 175–185 °C
• Thermal degradation: >230 °C
• Key behavior: low melt strength, sensitive to overheating

Polystyrene relies primarily on temperature and time, not high pressure, for good inter-pellet fusion.

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Plate Geometry & Mass

• Final size: 61 × 61 cm
• Thickness: 13 mm (1.3 cm)

Mass calculation

Volume = 61 × 61 × 1.3 = 4,837 cm³
Mass   = 4,837 × 1.05 ≈ 5,080 g

Recommended pellet charge: 5.25–5.35 kg

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Press Capability

• Maximum force: 20 tons ≈ 196 kN
• Platen size: 65 × 65 cm (0.4225 m²)

Maximum achievable pressure

196,000 N / 0.4225 m² ≈ 0.46 MPa ≈ 4.6 bar

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Controller Scaling Model

• x = 0–1000 → 0–100 % of total duration
• max = 200 → 200 °C = 100 %

Examples:

• y = 900 → 180 °C
• y = 450 → 90 °C

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Temperature Profile (Safe / First Run)

{
  "duration": 2400000,
  "max": 200,
  "controlPoints": [
    { "x": 0, "y": 500 },
    { "x": 250, "y": 900 },
    { "x": 600, "y": 900 },
    { "x": 750, "y": 900 },
    { "x": 1000, "y": 450 }
  ]
}

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Pressure Profile

{
  "max": 100,
  "controlPoints": [
    { "x": 0, "y": 0 },
    { "x": 500, "y": 0 },
    { "x": 600, "y": 30 },
    { "x": 700, "y": 70 },
    { "x": 900, "y": 70 },
    { "x": 1000, "y": 0 }
  ]
}

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Key Rules

• Never exceed 200 °C
• Apply pressure only after full melt
• Cool through Tg under pressure
• Vent molds properly
• Expect 0.4–0.6 % shrinkage

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Conclusion

This document provides a conservative, production-safe baseline for pressing GPPS polystyrene sheets from pellets using a programmable press.