How to test the thermal stability of CaCO3-filled compounds

This guide covers standard test methods, specimen preparation, operation steps, key evaluation indicators, and professional testing notes specifically for GCC/PCC calcium carbonate filled plastics, TPEs, rubber and polymer composites.

1. Core Conventional Test Methods & Standards

1.1 Thermogravimetric Analysis (TGA) — Fundamental Thermal Degradation Test

Standards: ISO 11358, ASTM E1131

Purpose

Evaluate initial degradation temperature, weight loss rate, thermal decomposition behavior, and distinguish resin matrix degradation from CaCO₃ thermal decomposition.

Test Operation

1. Specimen: 5–10 mg small granular/powder sample from compound pellets.
2. Atmosphere:
   • Nitrogen (N₂): Test pure thermal stability (no oxidation).
   • Air: Test realistic thermal oxidative stability (simulate service environment).
3. Heating program: Room temperature → 900 ℃, heating rate 10 ℃/min (standard).
4. Record real-time weight loss curve.

Key Evaluation Parameters for CaCO₃ Compounds

• Tonset​: Onset thermal degradation temperature of polymer matrix
• T5%​: Temperature at 5% weight loss (most intuitive stability index)
• Residual weight: Verify actual CaCO₃ filling content
• CaCO₃ decomposition temperature: ~820–880 ℃ (decompose into CaO + CO₂)

1.2 Differential Scanning Calorimetry (DSC) & Oxidation Induction Time (OIT)

Standards: ISO 11357, ASTM D3418

Purpose

Test glass transition temperature (Tg​), melting point (Tm​), crystallinity, and OIT (Oxidation Induction Time) — the core index for thermal oxidation stability.

OIT Test Method

1. Heat sample to constant temperature (e.g., 200 ℃) under nitrogen atmosphere.
2. Switch to air/oxygen and keep isothermal.
3. Record time until exothermic oxidation reaction occurs.

Longer OIT = better thermal oxidative aging resistance of CaCO₃-filled compounds.

1.3 Hot Air Oven Thermal Aging Test (Long-Term Service Stability)

Standards: ISO 188, ASTM D3045

Purpose

Simulate long-term high-temperature service, evaluate mechanical property retention and color change.

Test Procedure

1. Specimen: Standard dumbbell tensile bars, rectangular test strips.
2. Aging temperature (selected per polymer matrix): 70 ℃ / 85 ℃ / 100 ℃ / 120 ℃.
3. Aging time gradient: 72 h, 168 h, 336 h, 500 h.
4. After aging: Cool to room temperature, test:
   • Tensile strength & elongation at break retention rate
   • Hardness change
   • Yellowing index / surface discoloration

1.4 Heat Deflection Temperature (HDT) & Vicat Softening Temperature (VST)

Standards:

• HDT: ISO 75, ASTM D648
• Vicat: ISO 306, ASTM D1525

PurposeEvaluate thermal mechanical stability under load.

CaCO₃ filling usually increases HDT/VST, reflecting improved thermal rigidity and heat resistance under external load.

1.5 Auxiliary Morphology & Coupled Test

• SEM: Observe interface debonding, voids and CaCO₃ agglomeration after thermal aging.
• TGA-FTIR: Analyze volatile gas components (CO₂ from CaCO₃ decomposition, small-molecule pyrolysis products from resin).

2. Specimen Preparation Rules for CaCO₃-Filled Compounds

1. Compound uniformly via twin-screw extrusion, then injection/compression molding standard specimens.
2. Dry pretreatment: Bake samples at 80 ℃ for 2–4 h to remove absorbed moisture (CaCO3 easily absorbs water, causing false weight loss in TGA).
3. Ensure consistent particle dispersion; avoid agglomeration which distorts thermal stability data.
4. Set blank group (unfilled pure resin) and gradient CaCO₃ loading groups (20% / 40% / 60% etc.) for comparison.

3. Standard Step-by-Step Test Workflow

1. Prepare formula groups with different CaCO₃ loading and surface treatment types.
2. Dry and make standard test specimens.
3. Short-term thermal stability: TGA + DSC (OIT).
4. Thermal mechanical stability: HDT & Vicat test.
5. Long-term aging stability: Hot air oven aging + mechanical & color testing.
6. Compare data to judge the influence of CaCO₃ loading, particle size and surface modification on thermal stability.

4. Key Judgment Criteria

1. Higher Tonset​ / T5%​ → better thermal degradation resistance.
2. Longer OIT → better thermal oxidation stability.
3. Higher HDT/VST → better thermal rigidity under load.
4. Higher mechanical property retention after aging → better long-term thermal stability.
5. Lower yellowing degree → better thermal anti-aging performance.

5. Critical Testing Notes for CaCO₃ Systems

1. Choose air atmosphere preferentially for simulating actual application; nitrogen only for pure thermal decomposition analysis.
2. Surface-modified CaCO₃ (stearic acid coated) has higher thermal stability than unmodified raw CaCO₃.
3. Moderate CaCO₃ loading improves thermal stability; excessive loading causes interface defects and reduces aging resistance.
4. Strictly remove moisture; free water will lead to early weight loss and inaccurate TGA results.
5. Control heating rate at 10 ℃/min for repeatable and comparable data.