Experimental Analysis of the Pyrolysis Characteristics of Sawdust–PVC Blends: Thermogravimetric Test

The pyrolysis characteristics analysis experiment for sawdust and polyvinyl chloride (PVC) is a thermal analytical study that quantifies how wood sawdust, PVC, and their blends decompose under controlled, oxygen-free heating using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and coupled evolved-gas techniques. This article explains the testing samples, measured parameters, experimental methods, kinetic analysis approach, and practical applications of the results in co-pyrolysis, waste-to-energy conversion, and wood-plastic composite recycling.

Technical Overview

The sawdust–PVC pyrolysis characteristics analysis experiment is designed to determine the decomposition behavior of wood sawdust, PVC, and their binary blends under controlled inert-atmosphere heating. The experiment typically combines thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), and coupled evolved-gas techniques such as TG–FTIR and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). The outputs include decomposition stage temperatures, mass-loss rates, residual char yields, heat-flow behavior, apparent kinetic parameters, and the composition of gaseous and condensable products.

Wood sawdust, a lignocellulosic biomass, decomposes through the sequential degradation of hemicellulose (approximately 220–315 °C), cellulose (approximately 315–400 °C), and lignin, which degrades slowly across a broad range from roughly 160 °C to 900 °C. PVC, in contrast, decomposes in two well-defined stages: an initial dehydrochlorination step between about 200 °C and 360 °C that releases hydrogen chloride (HCl) and accounts for roughly 60–65% of the total mass loss, followed by main-chain scission, cyclization, and aromatization between about 400 °C and 550 °C that generates benzene-rich volatiles and a stable carbonaceous char.

When the two materials are co-pyrolyzed, measurable interactions occur. HCl released from PVC can catalyze cellulose dehydration and promote char formation, shifting the biomass decomposition peak toward lower temperatures, while alkali and alkaline-earth metals naturally present in biomass ash (potassium, calcium, magnesium) can partially capture chlorine as stable inorganic chlorides and suppress HCl emission. Quantifying these synergistic or antagonistic effects is the central scientific objective of the experiment, and the resulting data directly support reactor design, fuel blending optimization, chlorine management, and recycling process development.

Testing Samples

Wood Sawdust Samples

Sawdust from a documented species (for example, pine, fir, poplar, or mixed softwood) is air-dried, milled, and sieved to a particle size below 0.25 mm to minimize heat- and mass-transfer gradients inside the sample. The milled sawdust is then oven-dried at 105 °C for 24 hours and stored in a desiccator prior to testing. Baseline characterization records moisture, volatile matter, ash, fixed carbon, elemental composition, and calorific value so that thermal data can be interpreted against the fuel properties of the specific feedstock.

PVC Samples

Suspension-grade PVC resin powder of documented average polymerization degree is the preferred material for mechanistic studies, because commercial PVC compounds contain plasticizers, stabilizers, and fillers that alter the decomposition profile. The resin is dried to constant mass to remove absorbed moisture. Real-world rigid PVC waste or wood-plastic composite (WPC) scrap can be tested in parallel, but the additive composition should be characterized and reported, since calcium carbonate fillers and heat stabilizers noticeably shift the dehydrochlorination window and char yield.

Sawdust–PVC Blend Samples

Binary blends are prepared at defined mass ratios, commonly 75:25, 50:50, and 25:75, by thorough mechanical mixing or kneading to achieve macroscopic homogeneity. Pure sawdust (100:0) and pure PVC (0:100) are tested under identical conditions as reference samples. The reference curves are essential because they allow the experimentally measured blend curves to be compared with calculated weighted-average curves, which is the standard approach for identifying and quantifying interaction effects between the two components.

Testing Items

The experiment evaluates the following parameters for each sample and blend ratio:

• Thermogravimetric (TG) mass-loss curves and derivative thermogravimetric (DTG) profiles over the full temperature program.
• Characteristic temperatures: initial decomposition (onset) temperature, temperatures of maximum mass-loss rate (DTG peak temperatures), and terminal decomposition temperature.
• Stage-wise mass losses and residual char yields at the final temperature (typically 600–900 °C).
• Maximum mass-loss rates and the temperature span of each decomposition stage.
• Heat-flow behavior from DSC, including endothermic and exothermic events and their approximate enthalpies.
• Apparent kinetic parameters: activation energy, pre-exponential factor, and candidate reaction mechanism as a function of conversion.
• Evolved-gas composition and release profiles: HCl, CO, CO2, CH4, light hydrocarbons, carbonyl compounds, and aromatics such as benzene, toluene, naphthalene, and chlorinated benzenes.
• Synergistic effect indicators, expressed as the deviation between experimental and calculated TG/DTG curves of the blends.
• Baseline fuel characterization: proximate analysis (moisture, volatile matter, ash, fixed carbon), ultimate analysis (C, H, N, S), total chlorine content, and gross calorific value.

Testing Methods

Sample Pretreatment and Baseline Characterization

Moisture, ash, volatile matter, and calorific value of the sawdust are determined according to ISO 18134, ISO 18122, ISO 18123, and ISO 18125, respectively. Ultimate analysis of carbon, hydrogen, and nitrogen follows ISO 16948, while total sulfur and chlorine are measured per ISO 16994. The chlorine content of the PVC component can be verified according to ISO 1158. These baseline data enable a chlorine mass balance across the pyrolysis experiment, which is critical for assessing how much chlorine is released as HCl versus retained in the solid residue.

Thermogravimetric Analysis (TGA/DTG)

Thermogravimetric tests are performed on a simultaneous thermal analyzer in accordance with ISO 11358-1 and ASTM E1131. A representative sample of 5–10 mg is spread as a thin, even layer in an open alumina crucible to limit internal thermal gradients. High-purity nitrogen (99.999% or better) serves as the purge gas at a flow rate of 60–100 mL/min. The furnace temperature is ramped from ambient or 40 °C to 900 °C at multiple heating rates, typically 5, 10, 20, and 40 K/min, because the multi-rate dataset is required for iso-conversional kinetic analysis. Blank runs are executed for buoyancy correction, and each condition is tested at least in duplicate with mass-loss repeatability within approximately 1–2%. Decomposition stages are assigned from DTG minima, and compositional interpretation of the TG curve follows the framework of ASTM E1131.

Differential Scanning Calorimetry (DSC)

Heat flow is recorded either simultaneously on the TGA–DSC instrument or in separate DSC runs following the ISO 11357 series under nitrogen at the same heating rates. DSC identifies endothermic events such as dehydrochlorination and polyene chain melting, and exothermic events associated with cross-linking and char formation. Where reaction heats are of interest, kinetic constants derived from DSC exotherms may be evaluated according to ASTM E698 or ASTM E2890, and short-term thermal stability can be cross-checked per ASTM E2550.

Model-Free Kinetic Analysis

Apparent activation energies are extracted from the multi-rate TG data using iso-conversional methods, including the Kissinger method, the Ozawa–Flynn–Wall (OFW) method, the Kissinger–Akahira–Sunose (KAS) method, and the Friedman differential method. The analysis assumes single-step kinetics of the form dα/dt = A·exp(−Ea/RT)·f(α) over narrow conversion intervals, and activation energy is reported as a function of conversion between 0.05 and 0.90 together with the corresponding coefficient of determination. Coats–Redfern model fitting is then applied to discriminate among candidate mechanism functions and to estimate the pre-exponential factor. Typical results show apparent activation energies of roughly 60–110 kJ/mol for the main sawdust decomposition stage, approximately 80–130 kJ/mol for PVC dehydrochlorination, and approximately 140–210 kJ/mol for the second PVC stage, with blend values that deviate from weighted averages, confirming interaction between the components.

Evolved Gas Analysis (TG–FTIR and Py–GC/MS)

For online gas monitoring, the TGA exhaust is transferred through a heated line and gas cell maintained at 200–280 °C to prevent condensation, and FTIR spectra are collected continuously from 4000 to 500 cm⁻¹. The Gram–Schmidt reconstruct provides the total evolution profile, while characteristic bands identify individual species: HCl near 2880 cm⁻¹, CO2 near 2350 and 670 cm⁻¹, CO near 2180 and 2110 cm⁻¹, CH4 near 3015 cm⁻¹, carbonyl compounds at 1750–1650 cm⁻¹, and aromatic C=C stretching near 1600–1500 cm⁻¹. Flash pyrolysis–GC/MS at 500–600 °C for 10–20 seconds resolves individual organics, including levoglucosan, furfural, and acetic acid from the sawdust, and benzene, toluene, styrene, naphthalene, and chlorobenzenes from the PVC fraction.

Synergistic Effect Evaluation

Calculated reference curves for each blend are generated as the mass-weighted average of the pure-component TG curves, and the deviation between the experimental and calculated curves quantifies the interaction effect. Positive deviations indicate suppression of volatilization and enhanced char formation, whereas negative deviations indicate promoted decomposition. A chlorine mass balance, comparing the cumulative HCl evolved with the total chlorine input determined by ISO 16994, estimates the fraction of chlorine fixed by biomass-derived minerals in the solid residue, which is a key parameter for downstream corrosion and emission control.

Applications

• Reactor design data, including temperature programming, residence time, and heat duty requirements, for rotary-kiln and fluidized-bed co-pyrolysis of biomass and plastic waste mixtures.
• Feedstock evaluation for co-pyrolysis liquid fuel production, where PVC-derived hydrogen-rich volatiles can improve the hydrogen-to-carbon ratio of bio-oil while chlorine tracking guides dechlorination strategies such as lime addition or two-stage pyrolysis.
• Corrosion and emission control in waste incineration and gasization plants, where HCl release profiles inform acid-gas cleaning system sizing and support chlorine classification of solid recovered fuels per EN ISO 21640 and EN 15359.
• Recycling process development for wood-plastic composite (WPC) waste and mixed biomass-plastic streams.
• Kinetic databases for process simulation and CFD modeling, enabling scale-up studies from laboratory data to industrial equipment.
• Academic and industrial research on biomass–plastic synergistic pyrolysis mechanisms, chlorine capture chemistry, and char formation pathways.

FAQ

Why does PVC decompose in two distinct stages?

The first stage is dehydrochlorination: labile structural defects in the polymer chain initiate an unzipping elimination reaction that releases HCl between roughly 200 °C and 360 °C, removing most of the chlorine content. The second stage, between about 400 °C and 550 °C, involves scission of the conjugated polyene chains formed in stage one, accompanied by cyclization and aromatization, which produces benzene-rich volatiles and leaves a thermally stable char.

Is there a synergistic effect between sawdust and PVC during co-pyrolysis?

Yes, in most studies. HCl released from PVC can accelerate biomass dehydration and char formation and shift the sawdust DTG peak, while biomass-derived minerals capture part of the chlorine as stable inorganic chlorides. Many blends show reduced apparent activation energies and lower HCl yields relative to additive predictions. The magnitude and direction of the effect depend on blend ratio, heating rate, and ash composition, which is why experimental verification for each specific feedstock combination is necessary.

What heating rates and atmospheres are used?

Tests are conducted under high-purity nitrogen at 60–100 mL/min with heating rates of 5 to 40 K/min from room temperature up to approximately 900 °C. Multiple heating rates are essential for iso-conversional kinetic analysis. Some experimental programs add oxidative runs in air to characterize combustion behavior and burnout of the residual char.

How is HCl release quantified?

Online TG–FTIR continuously tracks HCl evolution through its characteristic absorption band near 2880 cm⁻¹, producing a temperature-resolved release profile. For total quantification, the exhaust can be absorbed in water and analyzed by titration or ion chromatography, and the result is checked against the total chlorine input measured per ISO 16994 to close the chlorine mass balance.

Which standards govern this experiment?

The core thermal analysis standards are ISO 11358-1 and ASTM E1131 for thermogravimetry, ASTM E2550 for thermal stability, and the ISO 11357 series for DSC, with ASTM E698 and ASTM E2890 relevant to DSC-based kinetics. Fuel characterization follows ISO 18122, ISO 18123, ISO 18125, ISO 16948, and ISO 16994 for the biomass fraction, ISO 1158 for PVC chlorine content, and EN ISO 21640 and EN 15359 for solid recovered fuel classification. Work performed in accredited third-party laboratories ensures metrological traceability of the reported data.

How are activation energies calculated from the data?

Iso-conversional methods such as Kissinger, KAS, OFW, and Friedman are applied to TG runs recorded at three or more heating rates, yielding activation energy as a function of conversion without requiring a priori assumption of the reaction mechanism. Coats–Redfern fitting is then used to test candidate mechanism functions and derive the pre-exponential factor, completing the kinetic triplet used in reactor modeling.