Volatile Matter Determination in Recycled Materials: Testing Principles, Standards, and Applications

Volatile matter determination is a core quality-control test that quantifies moisture, residual monomers, solvents, and other evaporable substances in recycled plastics, rubber, fibers, and recovered fuels. Accurate measurement, performed by accredited third-party laboratories in accordance with ISO, ASTM, EN, and GB standards, helps manufacturers prevent processing defects, verify feedstock consistency, and satisfy recycled-content specifications. This article explains the technical principles, applicable standards, test methods, and practical applications of volatile matter testing for recycled materials.

Technical Overview

Volatile matter is defined as the fraction of a material's mass that is driven off when a sample is heated under precisely controlled thermal conditions. In recycled materials, this fraction typically comprises absorbed moisture, residual monomers and oligomers, processing additives, solvents, adhesives, surfactants from washing lines, and thermal-oxidative degradation by-products accumulated during the material's first service life, collection, sorting, and regranulation stages.

Because recycled feedstock is inherently more heterogeneous than virgin resin, its volatile content is a sensitive indicator of feedstock quality and reprocessing adequacy. Excessive volatiles are directly linked to production defects such as silver streaks, bubbles, porosity, and sink marks in injection molded parts; melt instability and foaming during extrusion; and hydrolytic molecular-weight loss in condensation polymers such as recycled PET and recycled polyamide. Volatile matter determination therefore serves as a fast, low-cost screening test for incoming material inspection, supplier qualification, and batch release in recycling operations.

Accredited third-party laboratories perform this testing using gravimetric oven methods, vacuum oven methods, hot milling for rubber compounds, high-temperature crucible methods for recovered solid fuels, and thermogravimetric analysis for full volatilization profiling, all traceable to recognized international and national standards.

Testing Samples

Recycled Thermoplastics

The most frequently tested category includes post-consumer and post-industrial recyclates such as rPET flakes and pellets, rHDPE, rLDPE, rPP, rPS, rABS, rPC, rPA, and rigid or flexible PVC recyclates. Acceptable sample forms include pellets, film flakes, regrind, agglomerate, and powder, provided the material is representative of the lot and free of visible foreign contamination.

Recycled Rubber and Elastomers

This group covers crumb rubber derived from end-of-life tires, reclaimed (devulcanized) rubber, recycled thermoplastic elastomers, and cryogenically ground rubber powders, where volatile matter reflects moisture uptake, oil content, and devolcanization residues.

Recycled Fibers and Textiles

Mechanically or chemically recycled polyester and nylon fibers, recovered cotton and wool, and textile-to-textile recyclates are tested to quantify finish oils, moisture, and residual processing chemicals that affect spinning and nonwoven performance.

Recovered Fuels, Fillers, and Bio-based Materials

Solid recovered fuels (SRF/RDF), recovered carbon black, biochar, recycled mineral fillers, and biomass-derived feedstocks are characterized by high-temperature volatile matter determination, which is a fundamental parameter in fuel classification and energy-content estimation.

Testing Items

Typical measurands reported in a volatile matter test report for recycled materials include:

• Total volatile matter content, expressed as mass percentage of the as-received sample
• Moisture content and loss on drying at 105 ± 2 °C to constant mass
• Volatile loss under vacuum oven conditions for temperature-sensitive polymers
• High-temperature volatile matter at 900 °C (covered crucible method) for recovered solid fuels
• Thermogravimetric volatilization profile from ambient temperature to 600 °C, resolving moisture, volatiles, and degradation stages
• Repeat determinations with calculated repeatability limits for statistical confidence

Testing Methods

Gravimetric Oven Method

A pre-conditioned, accurately weighed sample is placed in an open dish or crucible and heated in a ventilated oven at the standard-specified temperature, commonly 105 ± 2 °C for general plastics, for a defined duration or until constant mass is reached. After cooling in a desiccator, the sample is reweighed, and the volatile content is calculated as the percentage of mass loss relative to the original mass. For vinyl chloride resins and recyclates, ISO 1269 and GB/T 2914 specify the oven conditions and calculation rules; ISO 3671 covers aminoplastic materials.

Vacuum Oven Method

ASTM D2288 describes the determination of volatile loss of plastics in a vacuum oven, where reduced pressure allows evaporation of volatiles at lower temperatures. This minimizes thermal degradation of sensitive recycled polymers such as rABS, rPC, and rPVC, ensuring the measured mass loss reflects true volatilization rather than decomposition.

Hot Milling and Oven Method for Rubber

ISO 248 specifies procedures for determining the volatile-matter content of raw and reclaimed rubber using either a hot mill method, in which the sample is sheeted on a heated mill with moisture evaporation, or a controlled oven method. This is essential for reclaimed rubber lots where retained moisture and softener volatiles compromise downstream compounding and vulcanization.

High-Temperature Crucible Method for Recovered Fuels

For solid recovered fuels, EN 15402, ISO 562, and ASTM D3175 prescribe heating the analysis sample in a covered crucible at 900 ± 10 °C for exactly 7 minutes. The covered crucible excludes air so that only pyrolytic volatiles, not combustible material, are lost. Moisture is determined separately and deducted to obtain the dry volatile-matter value used in fuel classification.

Thermogravimetric Analysis (TGA)

ISO 11358 provides the general principles for thermogravimetry of polymers. A few milligrams of recycled material are heated under nitrogen at a programmed rate, typically 10 °C/min to 600 °C, producing a continuous mass-loss curve. TGA differentiates free moisture, low-boiling volatiles, primary polymer degradation, and carbonaceous residue, making it a powerful diagnostic tool for contaminant identification in mixed or unknown recyclates.

Applications

• Incoming inspection and supplier qualification of recycled resin lots before production release
• Validation of drying parameters, such as desiccant dryer temperature and residence time, prior to extrusion or injection molding of hygroscopic recyclates
• Support for recycled-content certification, eco-label verification, and compliance with recycled material specifications such as the GB/T 40006 series
• Root-cause investigation of processing defects including bubbles, silver streaking, foaming, and hydrolytic viscosity loss
• Research and development of washing, degassing, devolatilization, and regranulation processes in recycling lines
• Trade compliance, customs verification, and batch documentation for imported and exported recyclates

FAQ

What is the difference between moisture content and volatile matter?

Moisture refers specifically to water removed at or near 100 °C, whereas volatile matter encompasses all evaporable species, including water, residual monomers, solvents, plasticizers, and degradation products. Some standards report volatile matter including water, while others require a separate moisture determination and report volatile matter on a dry basis.

Why do recycled materials show higher volatile content than virgin resins?

Recycled feedstock carries residues from its first application, such as adhesives, inks, labels, and fillers, along with washing agents, surfactants, moisture absorbed during storage, and low-molecular-weight fragments generated by thermal-oxidative degradation during both service and reprocessing.

How much sample is required for testing?

Gravimetric oven methods typically require 5 to 20 grams of representative material per determination, while TGA requires only 5 to 20 milligrams. Laboratories generally recommend submitting at least 50 to 100 grams to allow replicate determinations and confirmatory testing.

What are typical acceptance limits for recycled plastics?

Commercial specifications for polyolefin regranulates commonly limit total volatiles to the range of 0.1 to 0.5 percent by mass. For condensation polymers such as rPET, melt processing demands far stricter moisture control, often below 0.005 percent, because trace water drives hydrolytic chain scission. Contractual limits should always be agreed between supplier and purchaser based on the intended application.

How are results reported and what precision can be expected?

Results are reported as mass percentage of volatile matter with the conditioning temperature and duration clearly stated. Repeatability and reproducibility limits depend on the governing standard, material homogeneity, and volatile level; homogenous regranulates typically yield replicate agreement within a few hundredths of a percent, while heterogeneous flake streams show wider scatter.