Reclaimed rubber composition analysis identifies and quantifies the polymer base, carbon black, inorganic fillers, process oils, and residual curing agents in devulcanized recycled rubber materials. By combining spectroscopic, chromatographic, thermogravimetric, and elemental techniques in accredited third-party laboratories, manufacturers can verify grade conformity with standards such as GB/T 13460, ASTM D5603, and ASTM D297. This article explains the main sample types, testing items, analytical methods, and industrial applications of reclaimed rubber composition analysis.
Technical Overview
Reclaimed rubber (also known as devulcanized or regenerated rubber) is produced by processing waste vulcanized rubber—primarily scrap tires, inner tubes, and industrial rubber scrap—through thermal, mechanical, chemical, or microwave devulcanization. The process partially cleaves sulfur crosslinks and restores thermoplasticity so that the material can be re-compounded, re-blended, and re-vulcanized. Unlike virgin rubber, reclaimed rubber is a complex multi-component mixture containing rubber hydrocarbon, carbon black, inorganic fillers, extender oils, residual crosslinking chemicals, and devulcanization additives.
Because the feedstock originates from mixed waste streams, lot-to-lot variability is inherently high, which makes systematic chemical characterization essential. Composition analysis supports grade classification, incoming material inspection, formulation verification, reverse engineering, and environmental compliance. As an indicative reference, commercial tire-derived reclaimed rubber typically falls within the following ranges:
- Rubber hydrocarbon (NR/SBR/BR blend): approximately 40–55%
- Carbon black: approximately 20–30%
- Ash and inorganic fillers (ZnO, silica, calcium carbonate, clays): approximately 8–15%
- Solvent extract (process oils, softeners, residual organic additives): approximately 10–20%
- Volatile matter: typically below about 1.5–4%, depending on grade
The relevant standards ecosystem includes GB/T 13460 (specification for reclaimed rubber), ASTM D5603 and ASTM D6270 (recovered and reclaimed rubber from scrap tires), ASTM D297 (standard methods for chemical analysis of rubber products), and the ISO 9924 series (compositional analysis of rubber by thermogravimetry).
Testing Samples
Composition analysis can be performed on virtually all commercial grades of reclaimed rubber as well as on finished compounds that contain it. Common sample categories submitted to accredited third-party laboratories include the following:
Tire-Derived Reclaimed Rubber
Whole-tire and tread-derived grades represent the largest volume of reclaimed rubber on the market. The polymer phase is typically a blend of natural rubber, styrene-butadiene rubber, and butadiene rubber, heavily loaded with carbon black, silica, zinc oxide, and aromatic process oils. Analysis focuses on rubber hydrocarbon content, carbon black loading, and ash composition for grade conformity.
Butyl Reclaimed Rubber (IIR)
Recovered from scrap inner tubes, curing bladders, and butyl-based sealing products. Butyl reclaimed rubber retains the low gas permeability and heat resistance of the original polymer, making polymer purity and halobutyl contamination checks important analysis targets.
EPDM Reclaimed Rubber
Produced from scrap EPDM profiles, roofing membranes, and automotive sealing systems. Composition analysis verifies the EPDM content, ethylene-propylene ratio indicators, peroxide or sulfur cure residues, and polyolefin contamination from mixed collection streams.
Nitrile (NBR) and Other Oil-Resistant Reclaimed Rubbers
Derived from oil seals, hoses, and fuel-contact components. Acrylonitrile content estimation, plasticizer identification, and oil-resistance verification are the key analytical objectives for these specialty grades.
Natural Rubber-Based Reclaimed Rubber
Sourced from latex products, NR inner tubes, and natural rubber factory scrap. Analysis emphasizes rubber hydrocarbon purity, protein and ash residues, and the detection of synthetic rubber adulteration.
Chloroprene (CR) and Specialty Reclaimed Rubbers
Recovered from neoprene-based cable jackets, belts, and weatherstripping. Chlorine content, filler identification, and cure system characterization are typically required.
Fine-Particle and Powdered Reclaimed Rubber
Micronized or spray-dried reclaimed powders used as modifiers in thermoplastics, asphalt, and low-cost compounds. In addition to composition, particle-associated additive migration and surface treatment identification may be examined.
Finished Compounds Containing Reclaimed Rubber
Vulcanized or unvulcanized products in which the reclaimed rubber blend ratio must be quantified, either for supplier verification, cost audits, or product failure investigations.
Testing Items
The core scope of a reclaimed rubber composition analysis typically covers the following items:
- Polymer identification and quantification: NR, IR, SBR, BR, IIR, EPDM, NBR, CR, and their blends
- Rubber hydrocarbon content, the primary grade classification parameter
- Carbon black content and approximate carbon black class estimation
- Ash content and inorganic filler identification: ZnO, SiO2, CaCO3, clays, talc, titanium dioxide
- Volatile matter and moisture content
- Solvent extract content (acetone and chloroform extracts), covering process oils, softeners, resins, and soluble organic additives
- Total sulfur, free sulfur, and residual curing agent assessment
- Metallic element determination: Zn, Ca, Mg, Al, Fe, Si, Ti
- Heavy metal screening for environmental compliance: Pb, Cd, Hg, Cr, As, and related restricted substances
- Additive identification: accelerators, antioxidants, antiozonants, and processing aids
- Full deformulation (formulation reverse engineering) with a complete percentage breakdown report
Composition testing is frequently bundled with supplementary physical properties—Mooney viscosity ML(1+4) at 100 °C, tensile strength, elongation at break, hardness, and density—to provide a complete material qualification package.
Testing Methods
Infrared Spectroscopy for Polymer Identification
Fourier-transform infrared spectroscopy (FTIR) performed on polymer films or pyrolysates in accordance with ASTM D3677 and GB/T 7764 is the primary screening technique for identifying the rubber base. Characteristic absorption bands distinguish natural rubber, SBR, butyl, EPDM, nitrile, and chloroprene phases, including their blends.
Thermogravimetric Analysis (TGA)
TGA per ASTM D6370, ISO 9924-1, and GB/T 14837 provides a single-run compositional profile: volatiles and moisture evolve at low temperature, oils and polymer decompose under nitrogen, carbon black oxidizes under an air or oxygen atmosphere, and the inorganic residue remains as ash. The distinctive decomposition steps of natural rubber and SBR under controlled conditions even allow estimation of blend ratios in tire-derived grades.
Classical Gravimetric Chemical Analysis
The reference procedures of ASTM D297 remain the backbone of quantitative composition analysis. Solvent extraction per ISO 1407 and GB/T 3516 quantifies extractable organic matter; carbon black is determined by pyrolytic or nitric acid digestion methods covered by ISO 1408; and ash content is measured by controlled incineration per ISO 247 and GB/T 4498.
Elemental and Inorganic Analysis
- ICP-OES, ICP-MS, or AAS for zinc, calcium, and trace heavy metals
- CHNS elemental analysis for total sulfur, nitrogen, and carbon content
- X-ray fluorescence (XRF) for rapid screening of inorganic fillers and restricted substances
- X-ray diffraction (XRD) for identification of crystalline fillers and zinc oxide residues
Chromatographic and Microscopic Techniques
Gas chromatography–mass spectrometry (GC-MS) of solvent extracts identifies individual softeners, accelerators, antioxidants such as amine and phenolic derivatives, and supports polycyclic aromatic hydrocarbon (PAH) screening of aromatic oils. Pyrolysis-GC/MS refines polymer and copolymer identification in difficult multi-rubber blends. Scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) characterizes filler morphology, dispersion, and elemental distribution.
Applications
Reclaimed rubber composition analysis is applied across the full value chain of rubber recycling and product manufacturing:
- Grade classification and factory quality control against the acceptance criteria of GB/T 13460, including rubber hydrocarbon content, ash, and volatile matter limits
- Incoming material inspection by manufacturers of tires, conveyor belts, hoses, footwear outsoles, molded goods, mats, and extruded profiles that purchase reclaimed rubber
- Deformulation and competitive benchmarking to support new compound development, cost reduction, and material substitution studies
- Devulcanization process optimization, tracking residual sulfur and crosslink fragments across different temperature, pressure, and chemical agent conditions
- Blend ratio quantification of reclaimed rubber in finished products for supplier audits and cost verification
- Environmental and regulatory compliance screening, including heavy metal and PAH checks aligned with RoHS-type and REACH-type requirements
- Trade inspection, certification documentation, and technical dispute resolution between buyers and sellers
- Failure analysis of products in which unknown or off-specification reclaimed rubber may have contributed to performance problems
FAQ
What is the difference between reclaimed rubber and vulcanized rubber crumb?
Vulcanized rubber crumb or powder is simply ground waste rubber whose crosslinked network is intact; it cannot flow or be re-vulcanized on its own. Reclaimed rubber has undergone devulcanization, which partially breaks sulfur crosslinks and restores plasticity so it can be processed and re-crosslinked like a conventional rubber ingredient. Composition analysis distinguishes the two by examining crosslink residue chemistry in combination with processing-related extract profiles.
Why is rubber hydrocarbon content such an important grading parameter?
Rubber hydrocarbon content reflects the effective polymer content available for re-vulcanization and directly correlates with mechanical performance and blending value. Higher hydrocarbon content means less filler and ash dilution, allowing the compounder to use the reclaimed rubber at higher loadings without unacceptable property loss. It is therefore a central acceptance criterion in specifications such as GB/T 13460.
Can the blend ratio of reclaimed rubber in a finished product be determined?
Yes. By combining TGA decomposition step analysis, FTIR polymer fingerprinting, and extract composition comparison against reference samples, laboratories can estimate the proportion of reclaimed rubber in a compound, typically with reasonable accuracy when reference materials are supplied.
How much sample is required and what is the typical turnaround time?
A representative sample of approximately 100–200 grams is generally sufficient for a full compositional workup, including replicate gravimetric determinations. Standard composition analysis is usually completed within five to ten working days; full deformulation projects involving multiple cross-confirmation techniques may require two to three weeks.
Is TGA alone sufficient for a complete composition analysis?
TGA provides a fast and reproducible breakdown of volatiles, oil, polymer, carbon black, and ash, but it cannot identify individual polymer types, specific additives, or filler identities. A complete characterization combines TGA with FTIR or pyrolysis-GC/MS for the organic phase, GC-MS for extractables, and ICP-OES, XRF, or SEM-EDS for the inorganic phase. Accredited third-party laboratories design the test plan according to the information the client needs.