Combustion and thermal characteristics of Korean wood species

Abstract

This study examined the combustion and thermal characteristics of domestic wood species in Korea. Wood was tested using a cone calorimeter according to the KS F ISO 5660-1 (2003) standard. The combustion properties of the wood were measured in terms of the heat release rate (HRR), total heat released (THR), mass lose rate (MLR), and ignition time (time to ignition; TTI). An optical microscope was used to determine the anatomical characteristics of wood. Also, the thermal properties were measured using thermogravimetric analysis (TGA) to determine the thermal stability of wood. The results of this experiment could be useful for fundamentals of guiding the combustion properties and thermal stability when using wood for various applications.

Full Article

Combustion and Thermal Characteristics of Korean Wood Species

Hyun Jeong Seo,^a,b Jung-Eun Park,^a and Dong Won Son ^a,*

This study examined the combustion and thermal characteristics of domestic wood species in Korea. Wood was tested using a cone calorimeter according to the KS F ISO 5660-1 (2003) standard. The combustion properties of the wood were measured in terms of the heat release rate (HRR), total heat released (THR), mass lose rate (MLR), and ignition time (time to ignition; TTI). An optical microscope was used to determine the anatomical characteristics of wood. Also, the thermal properties were measured using thermogravimetric analysis (TGA) to determine the thermal stability of wood. The results of this experiment could be useful for fundamentals of guiding the combustion properties and thermal stability when using wood for various applications.

Keywords: Combustion properties; Domestic wood; Cone calorimeter; Heat release rate; Mass loss rate; Thermogravimetric analysis

Contact information: a: Department of Wood Processing, Korea Forest Research Institute, Seoul 130-712, Korea; b: Forest Product & Biotechnology, College of Forest Science, Kookmin University, Seoul 02707, Republic of Korea; *Corresponding author: dongwon12@korea.kr

INTRODUCTION

Wood has various beneficial properties, e.g., it is environmentally friendly, sustainable, renewable, and mechanically strong. It is widely used for construction and furniture materials. The demand for wood applications in residential and commercial building construction has increased in recent years. However, when used as a construction material, wood is limited because of its flammability (Grexa and Lübke 2001; Lee et al. 2011; Seo et al. 2013, 2015; Lowden and Hull 2013).

Wood is composed of three main components (cellulose 22% to 29%, hemicellulose approximately 40%, and lignin 28% to 35%); these components are organic materials. All three components begin thermal decomposition at a temperature of approximately 200 °C. The temperature range for generating volatilized gases from the thermal decomposition temperature for the respective components is as follows: cellulose 250 to 400 °C, hemicellulose 200 to 300 °C, and lignin 280 to 500 °C (Yang et al. 2006; Chung and Spearpoint 2007; Lowden and Hull 2013; Son and Kang 2014). The complex chemical reactions during thermal decomposition processes form char, accompanying the changes in the heat and weight of materials. Lignin in wood is an amorphous polyphenolic plant constituent; its chemical structure (aromatic ring) is able to give a very high char yield, which can still reach 35% to 38% at 900 °C. Also, Hosoya et al. (2006) and Garcia-Perez et al. (2008) reported that lignin has the best heat-resistance (Hosoya et al. 2006; Garcia-Perez et al. 2008; Pelasz-Samaniego et al. 2014; Xing and Li 2014). When the heat source is applied to the wood, it produces a variety of combustion gases. The flammable gases are induced to ignition on the surface of wood by adding air. Another important characteristic in the combustion process for wood is the heat release rate (HRR). The HRR data efficiently assesses the relative heat contribution of materials according to the conditions of the material, such as thick, thin, untreated, or treated, under fire exposure (Delichatsios et al. 2003; White and Dietenberger 2010; Lowden and Hull 2013; Rabaçal et al. 2013).

In case of fire, the combustion and thermal properties of wood applied in buildings can be evaluated by applying elements such as the heat release rate, ignition time, and propagation velocity on the materials surface (KS F ISO 5660-1 2003); Gratkowski et al. 2006; Mouritz et al. 2006; White and Dietenberger 2010; Lee et al. 2011; Rabaçal et al. 2013). Heat release rate (HRR), total heat released (THR), and time to ignition (TTI) can be measured using a cone calorimeter, which can measure the heat release rate by utilizing the principle that oxygen is consumed during the burning times (KS F ISO 5660-1 2003). Thus, a cone calorimeter was used to measure various combustion characteristics for six domestic wood species (Red pine, Japanese larch, Japanese cedar, Manchurian Ash, Korean fir, and Giant dogwood) used for building construction in Korea.

The wood species were observed using an optical microscope to confirm the unique anatomical characteristics of each species. An optical microscope is widely used to observe wood specimens because it creates a magnified image of an object and magnifies the image to allow the user to analyze it.

The internal structures of each species were observed using this principle to distinguish any anatomical characteristics of the wood that could affect the combustion characteristics. Also, thermogravimetric analysis (TGA) was used for measuring the thermal stability and other properties, such as mass lose rate and thermal decomposition temperature of the wood species (Yang and Roy 1999; Kim et al. 2014). TGA is measured by adding the specimens to mass changing of the specimens according to the change of temperature rising as a function (Yang and Roy 1999; Kim et al. 2014; Seo et al. 2015). The TGA test was performed to determine the mass loss rate of the different wood species at temperatures ranging from 20 to 800 °C.

The aim of this research was to determine the combustion properties of domestic woods according to KS F ISO 5660-1 (2003), using a cone calorimeter. Also, the purpose of this study is to assess the thermal properties of domestic woods for use in building and furniture materials. TGA was used to determine the thermal behavior.

EXPERIMENTAL

Materials

In this experiment, six kinds of domestic wood species were used: red pine (Pinus densiflora), Japanese larch (Larix kaempferi), Japanese cedar (Cryptomeria japonica), Manchurian ash (Fraxinus mandshurica), Korean fir (Abies koreana), and giant dogwood (Cornus controversa). These wood species are commonly used for building and construction materials in Korea (Lee and Kim 2013). For testing with the cone calorimeter, the wooden specimens were sized at 100 mm 100 mm 10 mm, according to KS F ISO 5660-1 (2003).

Test specimens are presented in Fig. 1, and the physical properties of specimens are shown in Table 1.

Table 1. Density of the Specimens

For optical microscopy, the specimens were produced after visually confirming the third section (transverse section, radial section, tangential section) of the wood. Identified specimens were cut in the form of blocks 5 mm 5 mm 5 mm. The blocks were composed of flakes of size 15 to 20 μm using a sliding microtome to measure each section.

Methods

Optical microscopy

Optical microscopy (Carl Zeiss, DE/Axio Imager M1) was carried out to confirm the anatomical characteristics of the species. The flake woods were stained by safranin, then dehydrated with ethanol, and produced by the permanent preparates. Completed permanent preparates were observed and photographed, confirming the internal structure of the wood.

Cone calorimeter test

The cone calorimeter test was carried out according to KS F ISO 5660-1 (2003). The woods were conditioned to stabilization at 50% and 25 °C prior to testing. The experiments were conducted by placing the woods in the same holder in a horizontal position under the cone heater. The wooden specimens were heated with a heat flux of 50 kW/m². Before the test, wooden specimens were maintained at temperature 252 °C and a relative humidity of 505%. Figure 2 shows the cone calorimeter (Fire Testing Technology Ltd, UK) used in this experiment.

Thermogravimetric analysis (TGA)

The TGA (TA Instruments Inc., 2960 SDT, USA) was carried out to confirm the thermal properties of the wood. The differential thermal (DT) analysis method is a technique similar to differential scanning calorimetry. It has been used to determine the enthalpy change and mass loss of specimens (Yang and Roy 1999; Seo et al. 2015). The thermal degradation of the wood was measured under nitrogen flow in a range of 25 to 800 °C at a heating rate of 20 °C/min. Wood was milled to sizes of 100 to 120 mesh for this experiment.

RESULTS AND DISCUSSION

Combustion Properties

The combustion properties of six kinds of domestic wood species were estimated by cone calorimeter tests. During the experiment, the following parameters were determined: heat release rate (HRR), peak heat release rate (PHRR), total heat release (THR), and mass loss rate (MLR). In addition, CO and CO₂ gas emissions by each specimen were measured to determine the correlation between gas release and burning of the materials.

Heat release rate (HRR)

The HRR is a very important parameter for evaluating the fire characteristics of wood (Grexa and Lübke 2001; Lee et al. 2011). It represents the number of calories released by the surface area of the materials. Also, it is the best indicator of the risk associated with material burnings (Grexa and Lübke 2001; Seo et al. 2015). Figure 3 shows the HRR curves.

The HRR curve shapes typically show two peaks. Generally, the first peak results from char formation by carbonization in the surface of the wood (Pelasz-Samaniego et al. 2014; Son and Kang 2014). According to a report by Yang et al. (2003), the surface and inner temperature of wood increase with external heat flux. After that, wood pyrolysis begins to increase and char is formed on the surface of wood (Yang et al. 2003). As shown in the graph, the temperature range of the first peak was similar among the all the wood species. It was also similar to the thermal decomposition temperature of hemicellulose in progressing char formation. The second peak of the HRR curve corresponds to the gradual burning of the woods through the char layer. Grexa and Lübke (2001) report that this peak is unique and indicates the heat release rate of all wood. Table 2 shows the results of the cone calorimeter test.

Table 2. Results of Cone Calorimeter Test

The peak of heat release rate (PHRR) value is considered an important parameter that best expresses maximum intensity of HRR (Xu et al. 2015). The confirmed PHRR values of woods were as follows: red pine 201.72 kW/m²; Japanese larch 158.41 kW/m²; Japanese cedar 147.72 kW/m²; Manchurian ash 400.27 kW/m²; Korean fir 128.46 kW/m²; and giant dogwood 296.59 kW/m². The highest PHRR value was obtained for Manchurian ash, possibly because Manchurian ash is composed of a high density compared to other species.

As indicated in the graph, the calories in hardwoods (Manchurian ash and giant dogwood) were higher than in softwoods (red pine, Japanese larch, Japanese cedar, and Korean fir). Also, it was confirmed that the time to ignition was faster for softwoods than hardwoods. Wood is a porous material, so the emitted heat from the flame can be absorbed into the pores and pits of the wood (Evans 1991). Seo et al. (2015) and Kim and Drzal (2009) reported that an endothermic reaction can occur in the pores of the porous materials. It was determined that the pores of hardwoods are bigger than those of softwoods, and on the basis of microphotographic images. Materials with a high specific surface area showed that the heat absorbing reaction occurred between the pores (Fig. 4). Additionally, Lorenzetti et al. (2013) and Chen et al. (2013) reported that external heat can be absorbed into the pores of porous materials and that heat was measured at the time of the thermal analysis of the materials.

In the case of hardwoods, the extractives contained in the pores were thought to affect the time to ignition of the woods. Manchurian ash had the highest density and initial mass, and the residual rate of mass reduction was low compared with other species. This result also meant that a large amount of char formed from the extractives. Xing and Li (2014) reported that the char of hardwoods is harder than that of the softwoods, while Xu et al. (2015) reported that the rate of char differed depending on the species and density of woods. In this experiment, similar results compared with previous studies were confirmed.

Time to ignition (TTI) is an important parameter for evaluating the fire characteristics and flammability of materials (Li 2003; Lee et al. 2011). Figure 5 shows the TTI of the wood species. The TTI of Manchurian ash was the longest. It is proposed that this is because Manchurian ash has wider pores compared to the other species. Romagnosi et al. (2013) reported that the heat absorbing characteristics of the materials is due to pores within the materials.

Fig. 5. TTI of the wood species

The results suggest that the pores in the specimens caused an endothermic reaction, so that time to ignition was delayed on the surface of that species. Among the softwoods, the TTI of Japanese cedar was confirmed to be the shortest. Generally, softwood species possess resin canals containing a variable amount of resin. Hardwood species, however, have oil cells or crystalliferous cells containing crystal and silica (Boonstra et al. 2006; Kim and Kwon 2009). It was determined that the inclusions in the hardwoods affect the TTI of woods so that ignition is delayed compared with softwood.

Total heat release (THR)

The total heat release (THR) is the total amount of heat released during the combustion, emitted from the surface of the materials.

It is important to explain the potential for flame spread when a fire occurs (Grexa and Lübke 2001; Lee et al. 2011; Seo et al. 2015). Figure 6 shows the THR curve after the cone calorimeter test. As shown in the graphs, the THR curves exhibited a tendency similar to the results of HRR, and the highest content was in the Manchurian ash. Because Manchurian ash is wide ring porous, the species has high heat absorption capacity (Chung and Spearpoint 2007; White and Dietenberger 2010). Chung and Spearpoint (2007) reported that the hardwoods had high carbon content and would generate more heat than softwoods. This affected the HRR and THR value. The results of this experiment showed a trend similar to the previous research.

Figure 7 shows the test specimens after the cone calorimeter test, with the remaining ash after combustion of wood species respectively. The ash remaining after incineration of red pine, Manchurian ash, Korean fir, and Giant dogwood showed gray color. However, for Japanese larch and Japanese the ash specimens were dark brown. These differences must be attributable to the unique properties of components in wood species. However, addition research will be needed in order to account for ash color based on various chemical components of the wood.

Thermal properties

Thermal properties were measured by thermogravimetric analysis, which was conducted to determine the mass change in wood by the temperature increasing over time (Yang and Roy 1999; Chen et al. 2013; Zhang et al. 2014).

The TGA of an ideal composition was used to analyze substances such as volatile components (water, solvents), polymers, carbon-containing components, and ash (Seo et al. 2013). Figure 8 shows the thermal degradation behaviors.

All wood specimens exhibited degradation of cellulose that began at the temperature range of 200 to 250 °C. A peak in the first range indicated the gasification of moisture in the wood (Almeida et al. 2008; Fujii et al. 2011; Xing and Li 2014). Randriamanantena et al. (2009) reported that the peak in the second range represents a unique thermal decomposition temperature of the species. Thermal decomposition temperatures of the woods by TGA were recorded as 320.31 °C for red pine, 335.47 °C for Japanese larch, 330.73 °C for Japanese cedar, 335.47 °C for Manchurian ash, 344.88 °C for Korean fir, and 364.32 °C for giant dogwood. These findings suggest that the thermal decomposition of cellulose and hemicellulose woods is in progress in earnest starting at temperatures in the range 300 to 400 ^oC (Seo et al. 2013; Zhang et al. 2014).

The effect of heating rate on weight loss rate (DTG) means the starting point of char formation or pyrolysis on the materials. Approximately 41.62 ^oC, red pine starts to form char. In the case of pyrolysis of Japanese larch, it began at approximately 58.17 ^oC. Also, Japanese cedar was 56.79 ^oC, Manchurian ash was 54.89 ^oC, Korean fir was 48.08 ^oC, and giant dogwood was 61.06 ^oC starting pyrolysis respectively. In addition, the peak of curve appears between 300 °C and 360 ^oC in all species. In this temperature range, pyrolysis of red pine proceeded radically. The period of char of the materials to be broken was also in this temperature range.

CONCLUSIONS

In this study, the combustion properties of domestic woods were investigated according to KS F ISO 5660-1 (2003) using a cone calorimeter. Thermal properties were measured by thermogravimetric analysis. The aim of this study was to provide basic information about domestic woods for the database of research for improving fire safety. A tendency was noted that the peak of heat release rate of the hardwood appeared at higher temperature than that of softwood. However, in the thermogravimetric analysis, it showed a similar tendency to the pyrolysis properties of the five kinds of species.

1. A cone calorimeter test was conducted to determine the combustion characteristics of domestic woods. The maximum PHRR was shown to be 400.27 kW/m² for Manchurian ash. The minimum PHRR was confirmed to be 128.46 kW/m² for Korean fir. In the case of THR, the highest value measured was for giant dogwood, at 103.06 MJ/m². The lowest value of THR was confirmed for Korean fir, at 64.81 MJ/m². Based on these results, it was determined that the HRR and THR were associated.
2. The TTI of Manchurian ash was the longest of all the woods, and that of Japanese cedar was confirmed to be the shortest. PHRR, TTI, and THR are all associated with each other, and they are capable of determining the fire hazard and possibility of fire spread.
3. The thermal decomposition temperature of domestic woods measured by TGA are as follows: red pine 320.31 °C, Japanese larch 335.47 °C, Japanese cedar 330.73 °C, Manchurian ash 335.47 °C, Korean fir 344.88 °C, and giant dogwood 364.32 °C.

REFERENCES CITED

Almeida, A. L. F. S. D., Barreto, D. W., and Calado, V. J. (2008). “Thermal analysis of less common lignocellulose fibers,” J. Therm. Anal. Calorim. 91(2), 405-408. DOI: 10.1007/s10973-007-8606-6

Boonstra, M. J., Rijsdijk, J. F., Sander, C., Kegel, E., Tjeerdsma, B., Militz, H., Van Acker, J., and Stevens, M. (2006). “Microstructure and physical aspects of heat treated wood. Part 1. Softwoods,” Maderas. Ciencia y Tecnología 8(3), 193-208. DOI: 10.4067/S0718-221X2006000300006

Chen, X., Huo, L., Jiao, C., and Li, S. (2013). “TG-FTIR characterization of volatile compounds from flame retardant polyurethane foams materials,” J. Anal. Appl. Pyrol. 100, 186-191. DOI: 10.1016/j.jaap.2012.12.017

Chung, Y. J., and Spearpoint, M. (2007). “Combustion properties of native Korean wood species,” Int. J. Eng. Perform. Fire Codes 9(3), 118-125.

Delichatsios, M., Paroz, B., and Bhargava, A. (2003). “Flammability properties for charring materials,” Fire Safety J. 38(3), 219-228. DOI: 10.1016/S0379-7112(02)00080-2

Evans, P. (1991). “Differentiating “hard” from “soft” woods using Fourier transform infrared and Fourier transform spectroscopy,” Spectrochim. Acta A 47(9-10), 1441-1447. DOI: 10.1016/0584-8539(91)80235-B

Fujii, T., Mochidzuki, K., Kobayashi, S., and Sakoda, A. (2011). “Quick and simple analysis of lignocellulose ingredients by thermogravimetric analysis,” J. Jpn. Soc. Mater. Cycle Waste Manage. 22(5), 293-297. DOI: 10.3985/jjsmcwm.22.293

Garcia-Perez, M., Wang, S., Shen, J., Rhodes, M., Lee, W. J., and Li, C. Z. (2008). “Effects of temperature on the formation of lignin-derived oligomer during the fast pyrolysis of Mallee woody biomass,” Energ. Fuel. 22(3), 2022-2032. DOI: 10.1021/ef7007634

Gratkowski, M. T., Dembsey, N. A., and Beyler, C. L. (2006). “Radiant smoldering ignition of plywood,” Fire Safety J. 41(6), 427-443. DOI: 10.1016/j.firesaf.2006.03.006

Grexa, O., and Lübke, H. (2001). “Flammability parameters of wood tested on a cone calorimeter,” Polym. Degrad. Stabil. 74(3), 427-432. DOI: 10.1016/S0141-3910(01)00181-1

Hosoya, T., Kawamoto, H., and Saka, S. (2006). “Thermal stabilization of levoglucosan in aromatic substances,” Carbohyd. Res. 341(13), 2293-2297. DOI: 10.1016/j.carres.2006.06.014

Kim, S., and Drzal, L. T. (2009). “High latent heat storage and high thermal conductive phase change materials using exfoliated graphite nanoplateles,” Sol. Energ. Mat. Sol. C. 93(1), 136-142. DOI: 10.1016/j.solmat.2008.09.010

Kim, N. H., and Kwon, S. M. (2009). “Appearance pattern of resin canals in Pinus koraiensis and Larix kaemferi,” J. Kor. Wood. Sci. Technol. 34(1), 1-6.

KS F ISO 5660-1 (2003). “Reaction to fire test – Heat release smoke production and mass loss rate – Part 1: Heat release rate (Cone calorimeter method),” Korea Standards.

Lee, J. H., and Kim, D. (2013). “Combustion properties for tree species of major structural components of traditional wooden building,” J. Kor. Soc. Hazard Mitig. 13(3), 17-22. DOI: 10.9798/KOSHAM.2013.10.3.017

Lee, B. H., Kim, H. S., Kim, S., Kim, H. J., Lee, B., Deng, Y., Feng, Q., and Luo, J. (2011). “Evaluating the flammability of wood-based panels and gypsum particleboard using a cone calorimeter,” Constr. Build. Mater. 25(7), 3044-3050. DOI: 10.1016/j/conbuildmat.2011.01.004

Li, B. (2003). “Influence of polymer additives on thermal decomposition and smoke emission of poly(vinyl chloride),” Polym. Degrad. Stab. 82(3), 467-476. DOI: 10.1016/S0141-3910(03)00201-5

Lorenzetti, A., Besco, S., Hrelja, D., Roso, M., Gallo, E., Schartel, B., and Modesti, M. (2013). “Phosphinates and layered silicates in charring polymers: The flame retardancy action in polyurethane foams,” Polym. Degrad. Stabil. 98(11), 2366-2374. DOI: 10.1016/j.polymdegradstab.2013.08.002

Lowden, L. A., and Hull, T. R. (2013). “Flammability behaviour of wood and a review of the methods for its reduction,” Fire Sci. Rev. 2(4), 1-19. DOI: 10.1186/2193-0414-2-4

Mouritz, A. P., Mathys, Z., and Gibson, A. G. (2006). “Heat release of polymer composites in fire,” Compos. Part A-Appl. S. 37(7), 1040-1054. DOI: 10.1016/j.compositesa.2005.01.030

Pelasz-Samaniego, M. R., Yadama, V., Garcia-Perez, M., Lowell, E., and McDonald, A. G. (2014). “Effect of temperature during wood torrefaction on the formation of lignin liquid intermediates,” J. Anal. Appl. Pyrol. 109, 222-233. DOI: 10.1016/j.jaap.2014.06.008

Rabaçal, M., Fernandes, U., and Costa, M. (2013). “Combustion and emission characteristics of a domestic boiler fired with pellets of pine, industrial wood wastes and peach stones,” J. Ren. Energ. 51, 220-226. DOI: 10.1016/j.renene.2012.09.020

Romagnosi, L., Gascoin, N., EI-Tabach, E., Fedion, I., Bouchez, M., and Steelant, J. (2013). “Pyrolysis in porous media: Part 1. Numerical model and parametric study,” Energy Convers. Manage. 68, 63-73. DOI: 10.1016/j.enconman.2012.12.023

Seo, H. J., Kim, S., Son, D. W., and Park, S. B. (2013). “Review on enhancing flame retardant performance of building materials using carbon nanomaterials,” J. Kor. Soc. Living Environ. 20(4), 514-526.

Seo, H. J., Kim, S., Huh, W., Park, K. W., Lee, D. R., Son, D. W., and Kim, Y. S. (2015). “Enhancing the flame-retardant performance of wood-based materials using carbon-based materials,” J. Therm. Anal. Calorim. 119(3), 1-8. DOI: 10.1007/s10973-015-4553-9

Son, D. W., and Kang, S. (2014). “Combustion properties of woods for indoor use (I),” J. Kor. Wood. Sci. Technol. 42(6), 675-681. DOI: 10.5658/WOOD.2014.42.6.675

White, R. H., and Dietenberger, M. A. (2010). “Fire safety of wood construction,” in: Wood Handbook-Wood as an Engineering Material, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI.

Xing, D., and Li, J. (2014). “Effects of heat treatment on thermal decomposition and combustion performance of Larix spp. wood,” BioResources 9(3), 4274-4287. DOI: 10.15376/biores/9.3.4274-4287

Xu, Q., Chen, L., Harries, K. A., Zhang, F., Liu, Q., and Feng, J. (2015). “Combustion and charring properties of five common constructional wood species from cone calorimeter tests,” Constr. Build. Mater. 96, 416-427. DOI: 10.1016/j.conbuildmat.2015.08.062

Yang, J., and Roy, C. (1999). “Using DTA to quantitatively determine enthalpy change over a wide temperature range by the “mass-difference baseline method,” Thermochim. Acta. 333(2), 131-140. DOI: 10.1016/S0040-6031(99)00106-9

Yang, L., Chen, X., Zhou, X., and Fan, W. (2003). “The pyrolysis and ignition of charring materials under an external heat flux,” Combust. Flame 133(4), 407-413. DOI: 10.1016/S0010-2180(03)00026-9

Yang, H., Yan, R., Chen, H., Zheng, C., Lee, D., and Liang, D. T. (2006). “In-depth investigation of biomass pyrolysis based on three major components: Hemicellulose, cellulose and lignin,” Energ. Fuel. 20(1), 388-393. DOI: 10.1021/ef0580117

Zhang, Z. X., Zhang, J., Lu, B., Xin, Z. X., Kang, C. K., and Kim, J. K. (2014). “Effect of flame retardants on mechanical properties, flammability and foamability of PP/wood–fiber composites,” Compos Part B-Eng. 43(2), 150-158. DOI: 10.1016/j.compositesb.2011.06.020

Article submitted: May 16, 2016; Peer review completed: June 26, 2016; Revised version received: June 30, 2016; Accepted: July 7, 2016; Published: July 21, 2016.

DOI: 10.15376/biores.11.3.7537-7550