The volatile matter content determination test is a critical quality-control procedure for evaluating the purity, processability, and safety of recycled plastic and rubber materials. By quantifying mass loss under controlled heating conditions, this gravimetric experiment reveals moisture, residual solvents, monomers, and degradation by-products that can compromise downstream processing and product performance. This article explains the technical principles, sample types, testing methods, standards, and practical applications of volatile matter testing for recycled materials.
Technical Overview
Volatile matter refers to the fraction of a material that evaporates or thermally desorbs when the sample is heated under specified conditions, typically expressed as a percentage of the original specimen mass. In virgin polymers, volatile content is usually low and tightly controlled during production. In recycled materials, however, the volatile fraction is often significantly elevated due to absorbed moisture, residual solvents from cleaning processes, unreacted monomers, degradation products generated during repeated thermal histories, printing inks, adhesive residues, label contaminants, and low-molecular-weight additives that migrate out of the polymer matrix.
Excessive volatile matter in recyclate causes a range of processing and quality defects. During extrusion or injection molding, volatiles generate bubbles, voids, silver streaks, and surface roughness in finished parts. Volatiles can also accelerate hydrolytic degradation in condensation polymers such as recycled PET and recycled polyamide, sharply reducing molecular weight and mechanical strength. Furthermore, certain volatile organic compounds released during processing may pose odor, workplace safety, and regulatory compliance concerns, particularly for applications in automotive interiors, packaging, and consumer goods.
The volatile matter determination experiment is therefore a fundamental incoming-inspection and batch-release test for recycled resins. The test is typically performed by accredited third-party laboratories, recyclers, compounders, and end-users following recognized standards such as ISO 1269, ISO 248-1, ASTM D2288, and corresponding national standards including GB/T 2914 and GB/T 24131.
Testing Samples
Recycled Polyolefins
Post-consumer and post-industrial recycled polyethylene (rPE), recycled polypropylene (rPP), and their copolymers are among the most frequently tested materials. These hydrocarbon polymers resist hydrolysis but readily absorb surface moisture from washing lines and may carry volatile contaminants from packaging residues.
Recycled Engineering Resins
Recycled PET, polyamide (rPA), polycarbonate (rPC), ABS (rABS), and polystyrene (rPS) demand particularly strict volatile control. Moisture-driven hydrolysis during melt processing of PET and PA can cause irreversible molecular-weight loss, making accurate volatile and moisture determination essential before extrusion.
Recycled Rubber and Elastomers
Ground tire rubber, reclaimed rubber, and thermoplastic elastomer regrinds are tested for volatile matter to assess the extent of oil, plasticizer, and processing-aid loss, as well as thermal degradation resulting from devulcanization or reclaiming processes.
Flakes, Regrind, and Powder Forms
Unprocessed recyclate forms, including washed bottle flakes, film flake, injection-molding regrind, and cryogenically ground powders, can be tested directly. Because these forms have larger surface areas than pellets, they generally exhibit higher and more variable volatile content, which the test quantifies for process planning.
Testing Items
Depending on the material specification and end-use requirements, the volatile matter experiment may include the following determinations:
- Total volatile matter content at 105 °C, reported as mass-loss percentage
- Moisture content distinguished from other volatiles via Karl Fischer titration
- Volatile organic compound (VOC) emission screening by headspace gas chromatography
- Thermal mass-loss profile across a programmed temperature ramp by thermogravimetric analysis
- Volatiles at application-specific temperatures, for example 160 °C to 230 °C for melt-processing simulation
- Odor-relevant volatile release evaluation for automotive and packaging grades
Testing Methods
Gravimetric Oven-Drying Method
The reference method follows the principle of ISO 1269, GB/T 2914, and ISO 248-1. A representative specimen of approximately 5 g is weighed into a pre-conditioned weighing bottle with a tight lid, and the initial mass is recorded with an analytical balance accurate to 0.1 mg. The sample is then heated in a ventilated oven at 105 °C ± 2 °C for a specified period, commonly 1 hour for plastics and longer durations for rubber materials. After heating, the bottle is transferred to a desiccator, cooled to ambient temperature, and reweighed. The volatile matter content is calculated as the percentage of mass lost relative to the original specimen mass. Duplicate determinations are standard, and results must agree within a defined repeatability limit.
Thermogravimetric Analysis (TGA)
TGA, performed in accordance with ISO 11358 or ASTM E1131, continuously records sample mass while temperature rises at a controlled rate under nitrogen purge. This method distinguishes low-temperature volatiles from thermal degradation of the polymer backbone and provides insight into the compositional profile of the recyclate, including moisture, oil, polymer, and inorganic filler or ash fractions within a single experiment.
Headspace Gas Chromatography
For applications requiring identification rather than simple quantification, headspace GC or GC-MS analysis separates and identifies individual volatile species released from the recycled material at elevated temperature. This technique is valuable for diagnosing contamination sources such as residual cleaning agents, fragrance carryover, or degradation products responsible for odor complaints.
Karl Fischer Titration
Where the specification requires specific water content rather than total volatiles, coulometric or volumetric Karl Fischer titration in accordance with ISO 15512 provides selective moisture determination with detection limits far below those of the gravimetric method, which is especially important for hydrolysis-sensitive resins such as recycled PET and recycled polyamide.
Applications
Volatile matter data from this experiment supports decision-making across the entire recycled-material value chain:
- Incoming quality control at compounders and converters to accept, reject, or re-grade recyclate lots
- Drying-process design, including residence time and temperature settings for desiccant dryers prior to extrusion
- Recycler batch certification and consistency verification between production lots
- Qualification of recyclate for demanding applications such as food-contact packaging layers and automotive interior components
- Research and development of stabilization packages, devolatilization screw designs, and vacuum-assisted extrusion strategies
- Failure analysis of bubble, void, and silver-streak defects traced to excess volatiles in the feedstock
FAQ
What is the typical temperature used in the volatile matter test?
The standard condition is 105 °C ± 2 °C, which removes absorbed water and low-boiling volatiles without significantly degrading most common polymers. For rubber and application-specific simulations, temperatures up to 150 °C or higher may be specified in the relevant test protocol.
How is volatile matter different from moisture content?
Volatile matter is the total mass loss under the test condition and includes moisture plus all other evaporating substances such as solvents, monomers, and oils. Moisture content, determined selectively by Karl Fischer titration, represents only water. The difference between the two values estimates the non-aqueous volatile fraction.
How much sample is required for the test?
A single determination typically uses approximately 5 g of representative material, and laboratories usually require 50 g to 100 g in total to perform duplicate measurements along with reserve specimens.
What volatile level is acceptable for recycled plastics?
Acceptance limits depend on the polymer and application. General-purpose recycled polyolefins are commonly specified below 0.5 percent, while recycled PET intended for melt processing often requires moisture below 0.005 percent to prevent hydrolytic degradation. The applicable purchase specification or product standard should always be consulted.
Can recycled flakes be tested as received without pelletizing?
Yes, flakes, regrind, and powders can be tested directly. Because of their higher surface area, such samples may show slightly higher volatile values than pelletized forms of the same material, so form-to-form comparisons should be interpreted with care.
