Volatile matter content testing is a critical quality control procedure for recycled plastics and reclaimed polymeric materials, quantifying moisture, residual solvents, monomers, and degradation byproducts that can compromise melt processing and final product performance. This article explains the principle, sample types, testing items, standardized methods, and industrial applications of volatile matter content testing for recycled materials, helping recyclers, compounders, and downstream manufacturers verify material quality and compliance with international standards.
Technical Overview
Volatile matter refers to the fraction of a material that is released as vapor when the sample is heated under controlled conditions. In recycled materials, the volatile fraction typically includes absorbed moisture, residual monomers and oligomers, solvents or detergents left over from washing and sorting operations, low-molecular-weight additives, and thermal or oxidative degradation products generated during the material's first service life and subsequent reprocessing.
Compared with virgin resins, recycled materials carry a significantly higher risk of excessive volatile content because of their complex contamination history. High volatile matter in recycled feedstock can lead to a range of processing and quality problems, including bubbles and voids in molded parts, silver streaks, surface defects, foaming during extrusion, hydrolytic molecular weight loss in polyesters and polyamides, mold and die deposits, unpleasant odor, and degraded electrical or mechanical properties.
The fundamental testing principle is gravimetric: a representative sample is weighed, heated at a specified temperature for a defined time (or scanned through a temperature program in thermogravimetric analysis), cooled under controlled conditions, and reweighed. The mass loss, expressed as a percentage of the original mass, is reported as the volatile matter content. Complementary instrumental techniques can further separate moisture from organic volatiles or identify specific volatile organic compounds.
Testing Samples
Recycled Thermoplastics (rPET, rHDPE, rLDPE, rPP)
Post-consumer and post-industrial recycled polyolefins and polyesters supplied as flakes, granules, or regranulated pellets. rPET flakes from bottle recycling are one of the most frequently tested categories, as trace moisture directly affects subsequent polymerization, solid-stating, and fiber or sheet production.
Recycled Engineering Plastics (rABS, rPC, rPA6, rPA66, rPOM)
Shredded or repelletized engineering resins recovered from electronic waste, automotive parts, and industrial scrap. These hygroscopic polymers require careful moisture and volatile screening before injection molding or extrusion.
Recycled PVC Compounds
Pulverized or regranulated PVC from cables, profiles, flooring, and pipes, where volatile matter testing follows well-established procedures originally developed for vinyl chloride polymers.
Recycled Rubber and Elastomers
Crumb rubber, devulcanized rubber, and reclaimed rubber compounds, for which volatile matter content serves as an indicator of processing history, moisture pickup, and thermal degradation.
Recycled Compounds, Masterbatches, and Textile Regranulates
Blended or modified recycled materials in which fillers, pigments, and additives interact with the volatile fraction and must be evaluated before conversion.
Sample handling requirements are strict: samples should be submitted in sealed, airtight packaging to prevent moisture exchange with the environment, sampling should be representative of the whole lot, and typical test portions range from approximately 5 g to 20 g for oven methods and 10 mg to 20 mg for thermogravimetric analysis.
Testing Items
- Total volatile matter content (% by mass, loss on heating at a specified temperature)
- Moisture and water content (loss on drying or Karl Fischer titration)
- Volatile organic compound (VOC) content and composition by headspace gas chromatography
- Volatile fraction distribution across temperature windows by thermogravimetric analysis
- Related compositional screening, including filler and ash content, to fully characterize the recycled feedstock
Testing Methods
Oven Gravimetric Method (Loss on Drying)
The test portion is weighed into a pre-conditioned vessel, heated in a ventilated or vacuum oven at a material-specific temperature, commonly 105 °C ± 2 °C for general thermoplastics or elevated temperatures for high-melting polyesters, then cooled in a desiccator and reweighed. Volatile matter content is calculated as the mass difference relative to the original mass. This approach is consistent with procedures such as ISO 1269 and GB/T 2914 for vinyl chloride polymers and ASTM D6980 for determining water in plastics by loss in weight.
Thermogravimetric Analysis (TGA)
A few milligrams to tens of milligrams of sample are heated at a constant rate under an inert nitrogen atmosphere. The mass loss occurring below the onset of polymer decomposition is attributed to volatiles, while switching to air or oxygen at higher temperatures allows filler and ash determination in the same run. TGA methods are performed in accordance with ISO 11358 for the thermogravimetry of polymers and ASTM E1131 for compositional analysis by thermogravimetry. TGA offers small sample requirements, precise temperature control, and the ability to distinguish the volatile window from the main decomposition region.
Karl Fischer Titration
For hygroscopic recycled polyesters and polyamides where moisture must be controlled to very low levels, coulometric or volumetric Karl Fischer titration according to ISO 15512 provides a water-specific result that is unaffected by other organic volatiles.
Headspace Gas Chromatography–Mass Spectrometry (GC-MS)
When odor, emissions, or migrating substances are of concern, headspace GC-MS identifies and quantifies individual volatile organic compounds released from the recycled material at elevated temperature, supporting root-cause investigation of contamination sources.
Key parameters influencing accuracy include the heating temperature and duration, furnace atmosphere, sample thickness and particle size, cooling and reweighing conditions, and the prevention of moisture reabsorption after heating. Accredited third-party laboratories control these variables and report results with measurement uncertainty and clear method references.
Applications
- Incoming quality control of recycled feedstock at recycling plants, compounders, and converters
- Specification verification between buyers and sellers of recycled resins and regrind
- Process optimization of washing, drying, degassing, and melt filtration stages in recycling lines
- Quality assurance for rPET used in fibers, sheets, strapping, and food-contact applications after regulatory suitability assessment
- Automotive interior components, where volatile content correlates with odor and fogging behavior
- Support for recycled-content certification, eco-labeling, and corporate sustainability reporting
- Research and development comparing different recycling routes, stabilizer packages, and contaminant removal efficiencies
FAQ
What is considered volatile matter in recycled materials?
It is the total mass lost upon heating under specified conditions, generally comprising moisture, residual solvents and detergents, monomers and oligomers, low-molecular-weight additives, and thermal degradation products.
Which heating temperature is used?
The temperature is material dependent. A general oven temperature of 105 °C is widely applied, while high-melting polymers such as PET may be tested at higher temperatures, for example around 150 °C, provided the polymer itself does not decompose. TGA methods define the volatile window instrumentally based on the decomposition onset.
How much sample is needed?
Oven gravimetric methods typically require 5 g to 20 g per determination, while TGA requires only about 10 mg to 20 mg. Duplicate determinations are recommended for lot release decisions.
What volatile content limit is typically specified?
Commercial specifications vary by polymer and application, but recycled materials are commonly required to remain below approximately 0.5 % total volatile matter, and hygroscopic polyesters used in melt processing often demand moisture levels far below this value to prevent hydrolysis. Limits should always be agreed between supplier and customer.
Can the test distinguish moisture from organic volatiles?
The gravimetric oven method reports total volatiles only. Karl Fischer titration provides a water-specific result, and headspace GC-MS identifies individual organic volatiles, so a combination of methods gives a complete picture.
Why do recycled materials show higher volatile content than virgin resins?
Collection, sorting, washing, and multiple heat histories introduce contaminants and degradation products that are absent or minimal in virgin polymers, so systematic volatile matter screening is an essential part of recycled material quality management.
How long does testing take?
Standard oven and TGA determinations are typically completed within one to three working days including conditioning and report issuance, while headspace GC-MS profiling may require additional time for compound identification.
