All samples were air-dried to constant weight and subsequently oven-dried at 105 ± 2˚C to determine moisture content ([3]-type procedure). Dried samples were milled and sieved to a particle size of 1 - 2 mm for proximate, ultimate and calorific determinations. For carbonisation tests whole pieces (≈3 - 5 cm) were used to better represent actual kiln behaviour.

Carbonisation was conducted in a controlled laboratory kiln following established procedures for charcoal production (slow pyrolysis). A slow heating ramp (<1˚C min⁻¹) was applied until the target temperature of 500 - 600˚C was reached, then held for 3 - 4 hours to ensure complete carbonisation. These temperatures and time ranges are commonly used for high-quality charcoal production and reflect recommendations from FAO [4] and recent comparative kiln studies. Kiln atmosphere was oxygen-limited; gas outlet was vented, and gases were condensed where appropriate. Replicate carbonisation runs (n = 3) were done for each material to assess repeatability.

Proximate analysis (moisture, volatile matter, ash, fixed carbon) was performed using standard methods analogous to those used for solid fuels and charcoal: moisture by oven drying (ASTM [3], volatile matter by loss-on-ignition at 950˚C [5], and ash by combustion at 575 ± 25˚C [6]. Fixed carbon was calculated by difference (100% − moisture − volatile matter − ash). These methods are widely used in biomass and charcoal characterisation and give directly comparable metrics across studies.

Elemental composition (C, H, N, S, O by difference) was measured on powdered charcoal using an elemental analyser that is CHNS-O analyser, following procedures in ASTM [3] for C/H/N. Sulfur was quantified to estimate potential SOx emissions upon combustion. For engineered wood specimens (MDF, particleboard, OSB), particular attention was given to nitrogen and sulfur because adhesives and additives can increase N and S levels and influence emissions.

Gross calorific (higher heating) value was determined using an adiabatic bomb calorimeter following [7] procedures: each sample pellet (~1 g) was combusted in an oxygen atmosphere and the temperature rise recorded; corrections for fuse wire and ignition were applied. Each sample was measured in triplicate and the mean reported. Calibration was done using a certified reference material (benzoic acid) before measurement.

All measurements were performed in at least triplicate. Results are reported as mean ± standard deviation. Statistical differences between species were evaluated using one-way ANOVA followed by Tukey’s HSD post-hoc test where appropriate (α = 0.05). Where non-normality was detected, non-parametric tests (Kruskal-Wallis) were used.

Carbonisation gases and condensates were handled in a fume hood or vented to a safe location. Residual ash and spent samples were disposed of following institutional hazardous-waste procedures when containing elevated heavy metals or additives.

The calorific value of the raw samples ranged from 17.30 MJ/kg to 18.40 MJ/kg, which is consistent with reported values for untreated wood and engineered wood composites ([8][9]). Makore recorded the highest pre-carbonisation calorific value (18.40 MJ/kg), followed by coconut wood (18.26 MJ/kg). Among the engineered wood products, plywood (17.90 MJ/kg) and OSB (17.67 MJ/kg) exhibited slightly higher energy content than MDF (17.30 MJ/kg), aligning with typical ranges for veneer-based and reconstituted boards ([10][11]). The standard deviations across duplicate measurements were low (0.055 - 0.166), indicating good repeatability and consistent fuel properties, consistent with findings for controlled biomass thermochemical characterisation [12].

Carbonisation resulted in a substantial increase in calorific values across all samples, rising into the range of 23.25 - 25.29 MJ/kg, which corresponds to expected values for high-quality charcoal ([13][14]). OSB recorded the highest calorific value after carbonisation (25.29 MJ/kg), followed by plywood (24.72 MJ/kg), MDF (23.52 MJ/kg), and Makore (23.25 MJ/kg). These values fall within the typical post-carbonisation energy levels reported for both natural hardwoods and engineered biomass feedstocks ([15][16]). The relatively higher calorific values observed in engineered wood samples are consistent with documented carbonisation behaviour of resin-bonded composites [17].

Comparison of the before and after carbonisation values showed calorific value increases of 26.36% (Makore), 35.90% (MDF), 38.11% (Plywood), and 43.12% (OSB). Increases of this magnitude align with previously reported improvement ranges (25% - 45%) observed in biomass carbonisation studies ([12][14]). The engineered boards exhibited the highest proportional gains in energy content, a trend supported by literature indicating that thermosetting resins contribute additional fixed carbon during pyrolysis, resulting in enhanced calorific value ([10][18]). Although Makore had the highest initial calorific value among the raw samples, its proportional increase after carbonisation was the lowest, a behaviour consistent with dense hardwoods that already possess high baseline lignin and carbon content ([8][15]).

Table 1. (a) Calorific values of samples before carbonization. (b) Calorific Value of samples after carbonization.

Table 2.(a) Ultimate analysis of samples before carbonization. (b) Ultimate analysis of samples after carbonization.

Table 3. (a) Proximate analysis of samples before carbonation. (b) Proximate analysis of samples after carbonation.

Natural wood species such as Makore and Coconut wood typically offer more predictable behaviour during carbonisation because they are primarily composed of cellulose, hemicellulose, lignin and minor extractives. Their caloric values increase from 18.40 MJ/Kg and 18.26 MJ/kg to 23.25 MJ/Kg and 23.39 MJ/Kg, respectively. In contrast, engineered wood products (MDF, particleboard, OSB, Plywood) with calorific values ranging from 17.30 MJ/Kg, 17.67 MJ/Kg, 17.76 MJ/Kg and 17.89 MJ/Kg before carbonisation rose to 23.53 MJ/Kg, 22.43 MJ/Kg, 25.29 MJ/Kg, and 24.71 MJ/Kg, respectively. These products incorporate resins (e.g., urea‑formaldehyde, phenol‑formaldehyde), fillers and adhesives, which can influence ash content, inorganic constituents (N, S, Cl), and emission propensity. Engineered boards pose formaldehyde and other emission risks due to adhesive chemistry [19]. Thus, when interpreting the results showing differences in ash yields, fixed carbon, or emission proxies between natural versus engineered wood species, this difference in feedstock chemistry likely contributes strongly.

The results obtained in this study for the six feedstocks (Makore, MDF, plywood, particleboard, OSB, Coconut wood) can be interpreted in the context of published literature on charcoal/carbonisation of wood and wood‑based materials. Several key themes emerge, such as feedstock composition and engineered versus natural wood, carbonisation method and yield, fuel quality (calorific value, fixed carbon), and emissions or environmental implications.

The yield of charcoal from wood depends on species (wood density, moisture, extractives) and on the carbonisation method (heating rate, final temperature, residence time, oxygen‐limitation) as well as sample size. A recent study from Sri Lanka found that a barrel method produced ~28% yield versus ~21% for pit method across three wood species, attributing differences to improved airflow/temperature control in barrel method [20]. Similarly, the FAO guidance emphasises that species selection (wood density, moisture) and kiln design affect charcoal quality and yield [21]. In this study, the method used which is a slow heating ramp (≈1 ˚C∙min⁻¹) to 500˚C ‑ 600˚C hold for 3 ‑ 4 h under oxygen‐limited conditions, falls within recommended ranges for high‑quality charcoal, and so the results are quite comparable to literature benchmarks. Yet, if the yields vary markedly (for example, engineered boards yielding lower fixed carbon or higher ash), this may be attributed to the added adhesives/fillers and perhaps less efficient carbonisation of non‑homogeneous feedstocks.

High quality charcoal as fuel is characterised by high fixed carbon, low moisture, low volatile matter, low ash content and high calorific value. The effect of species is strong: dense woods with low moisture content yield “heavy charcoal that burns for a long time” [20]. In the findings, the natural wood species (Makore, coconut wood) showed higher fixed carbon and calorific value compared to engineered products. This aligns with the literature: [22] found differences in physical/chemical properties of charcoal derived from different feedstocks. Engineered wood products often yield higher ash content and lower calorific value due to mineral fillers and adhesives [23].

Although this study may not have directly measured emissions (e.g., NOx, SOx, VOCs), it is worth discussing potential emission differences given the nature of feedstocks. Engineered wood feedstocks (with adhesives) may lead to higher emissions of sulfur or nitrogen compounds (from resin decomposition) and possibly higher ash with inorganic residues [24]. Also, from a sustainability viewpoint, the charcoal value chain must consider species selection, sustainable wood sourcing, and forest regeneration [25]. For Ghana, if charcoal production from such wood species is envisaged, it is critical to note that feedstock origin, sustainable harvesting, and kiln efficiency all affect the environmental footprint. Engineered wood residues may pose disposal/use challenges (ash, emissions), while natural wood species may provide cleaner fuels.

This trend is well-documented in biomass thermochemical conversion studies, where calorific values typically increase from 15 - 19 MJ/kg in raw wood to 23 - 30 MJ/kg in charcoal, due to moisture loss, devolatilisation, and enrichment of fixed carbon ([12][14]). Engineered board chars producing lower calorific values or higher ash are consistent with previous studies [23]. The calorific values of the samples studied fell within 22 - 25 MJ/Kg which is within documented values. The most significant outcome of carbonization is the dramatic increase in the calorific value (CV). This is directly related to the concentration of fixed carbon and the removal of non-combustible components like moisture and volatile matter.

The proximate analysis shows the most evident transformation from wood to charcoal. For Moisture and Volatile Matter: The 600˚C temperature is high enough to drive off nearly all moisture and volatile compounds. The resulting charcoal as depicted in the values are near-zero moisture content, increasing its stability and energy density. The volatile matter decreased from over 84% to below 5%, making the charcoal much slower to ignite but capable of a longer, more sustained burn. In relation to the Fixed Carbon (FC): As moisture and volatiles are released, the proportion of fixed carbon in the solid charcoal increases dramatically. This is the primary component responsible for charcoal’s high energy output. MDF, with the highest initial FC, yields charcoal with a very high Fixed Carbon, contributing to its prolonged burn time. The Ash Content: The percentage of ash increased in all samples because the inorganic mineral content concentrated as the organic matter is converted to gas and tar. Particle Board, with its highest initial ash, produced the highest-ash charcoal, reducing its fuel efficiency and potentially leading to more residue during combustion.

The ultimate analysis, focusing on elemental composition, reveals the environmental implications of the carbonization process. Carbon (C): The carbon percentage rose sharply in all samples, confirming the charcoal’s high energy potential. Nitrogen (N) and Sulfur (S): This is where the difference between natural wood and engineered wood becomes critical. The natural Woods: Makore and Coconut Wood, with low initial N and S, produced charcoal that generates minimal NOx and SOx emissions when burned. Whilst engineered Woods: MDF and Particle Board, containing nitrogen and sulfur-rich adhesives (like urea-formaldehyde), will retain these elements in the concentrated charcoal. Upon combustion, this will lead to the release of harmful NOx and SOx gases, as emphasised by [26]. OSB will also have higher emissions than natural wood, though potentially less than Particle Board.

Carbonisation markedly improved the energy density of all biomass samples, transforming them from moderate-energy wood fuels into high-grade charcoal materials suitable for industrial and domestic applications. This trend is well-documented in biomass thermochemical conversion studies, where calorific values typically increase from 15 - 19 MJ/kg in raw wood to 23 - 30 MJ/kg in charcoal, due to moisture loss, devolatilisation, and enrichment of fixed carbon ([12][14]). The calorific values obtained in this study (23.25 - 25.29 MJ/kg) fall within global benchmarks for high-quality charcoal ([13][16]), demonstrating the effectiveness of the carbonisation process.

Engineered wood products (MDF, Plywood, OSB) exhibited significantly greater increases in calorific value than natural Makore wood. This behaviour can be explained by their manufacturing composition. Composite boards contain thermosetting adhesives such as urea-formaldehyde (UF), phenol-formaldehyde (PF), or methylene diphenyl diisocyanate (MDI), which are known to carbonise into aromatic, carbon-rich char structures when heated ([10][11]). These resins contribute additional fixed carbon and enhance char yield compared to solid wood. Their compressed, high-density fibre structures also promote uniform devolatilisation and carbon retention during pyrolysis, contributing to the higher calorific values observed [17]. Consequently, OSB charcoal recorded the highest calorific value (25.29 MJ/kg), consistent with findings that long-strand composites and PF-bonded products exhibit superior thermal stability and carbonisation behaviour [18].

Makore wood, despite having the highest initial calorific value among raw samples, showed the lowest proportional increase after carbonisation. This is typical of dense hardwoods, where the initial fixed carbon content and structural lignin are already relatively high, leaving less room for proportional energy gain during pyrolysis ([8][12]). Nonetheless, its final calorific value of 23.25 MJ/kg remains within high-quality charcoal standards and aligns with reported values for tropical hardwood charcoals (19 - 25 MJ/kg) ([12][15]).

Overall, the results demonstrate that engineered wood waste materials can produce charcoal with calorific values equal to or exceeding those of natural wood species. This observation supports findings in circular bioeconomy research indicating that composite wood wastes—when thermochemically converted—offer substantial potential for sustainable fuel production, waste-to-energy applications, and biomass valorisation ([14][27]). The superior energy performance of OSB and plywood charcoal positions these engineered materials as viable feedstocks for industrial biomass energy systems, provided emissions from resin breakdown are appropriately controlled.