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Figure from:Characterization of Manmade and Recycled Cellulosic Fibers for Their Application in Building Materials

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Figure 11: FTIR spectra of RCF samples (4-6) in comparison to microcrystalline cellulose (MC

Figure 11 FTIR spectra of RCF samples (4-6) in comparison to microcrystalline cellulose (MC

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Figure 1: Greencel cellulosic fibers: wood pulp (a) and recycled wastepaper fibers (b) Two kinds of cellulosic fibers, from wood processing (mainly the sulfate beech tree cellulose) and recycling wastepaper, were used. Six cellulosic fibers samples were provided by the company Greencel Ltd. (Hencovce, Slovakia). As shown in Fig. 1, these samples are visually different in color. Samples 1-3 represent white wood pulps (WPs) and samples 4-6 correspond to gray recycled cellulosic fibers (RCFs).
Figure 1: Greencel cellulosic fibers: wood pulp (a) and recycled wastepaper fibers (b) Two kinds of cellulosic fibers, from wood processing (mainly the sulfate beech tree cellulose) and recycling wastepaper, were used. Six cellulosic fibers samples were provided by the company Greencel Ltd. (Hencovce, Slovakia). As shown in Fig. 1, these samples are visually different in color. Samples 1-3 represent white wood pulps (WPs) and samples 4-6 correspond to gray recycled cellulosic fibers (RCFs).
Table 1: Chemical composition of WP (1-3) and RC (4-6) fiber samples The lignin content is very low (< 0.5 percent) in WP samples (1-3) due to the bleaching process which is also related to the white color of the samples. In contrast, lignin is present in a relatively high “a Tab. 1 shows the chemical composition of the studied cellulosic fiber samples. As shown, two se cellulosic fiber samples (WP and RCF) differ in the content of a main component (hollocellulose). first high purity set of samples (1-3) is characterized by a high ho whereas the samples of the second set (4-6) have a lower holocellu relatively large difference in the cellulose content in the samples is also he WP samples (1 and 2) is approximately 81-82 percent, but this subs percent of the WP sample (3) and RCF (samples 4-6). The amount cellulose/hemicellulose ratio ranging between 1.7 to 2.3 what is simi 4.2-4.8) in the two WP samples (1 and 2). ose conten of hemicel ranges from 17-37 percent; the highest content is in sample 3. Four samples s of The ocellulose content > 99 percent, by 18-29 percent. observed. The cellulose portio ance 1s represented by only 47-62 A nin uloses in the sam ples (samples 3-6) have a ar to nanocellulose samples with ypical ratios between 1 and 2.2 [29]. As expected, the cellulose/hemicellulose ra io was relatively high
Table 1: Chemical composition of WP (1-3) and RC (4-6) fiber samples The lignin content is very low (< 0.5 percent) in WP samples (1-3) due to the bleaching process which is also related to the white color of the samples. In contrast, lignin is present in a relatively high “a Tab. 1 shows the chemical composition of the studied cellulosic fiber samples. As shown, two se cellulosic fiber samples (WP and RCF) differ in the content of a main component (hollocellulose). first high purity set of samples (1-3) is characterized by a high ho whereas the samples of the second set (4-6) have a lower holocellu relatively large difference in the cellulose content in the samples is also he WP samples (1 and 2) is approximately 81-82 percent, but this subs percent of the WP sample (3) and RCF (samples 4-6). The amount cellulose/hemicellulose ratio ranging between 1.7 to 2.3 what is simi 4.2-4.8) in the two WP samples (1 and 2). ose conten of hemicel ranges from 17-37 percent; the highest content is in sample 3. Four samples s of The ocellulose content > 99 percent, by 18-29 percent. observed. The cellulose portio ance 1s represented by only 47-62 A nin uloses in the sam ples (samples 3-6) have a ar to nanocellulose samples with ypical ratios between 1 and 2.2 [29]. As expected, the cellulose/hemicellulose ra io was relatively high
Table 2: Properties of Greencel cellulosic fibers (WP: 1-3; RCF: 4-6)
Table 2: Properties of Greencel cellulosic fibers (WP: 1-3; RCF: 4-6)
The bulk density of WP and RCF samples reached their average values ranging from 40 to 80 kg/m’. It is generally known that cellulosic fibers are low bulk density, closed-air polymeric materials in a porous structure. Therefore, the bulk density is always lower than the density. Fig. 3 shows that bulk density increases with decreasing average fiber length in the studied range of variables. The calculated value of the correlation coefficient (0.7663) confirms a moderate dependence between both of the mentioned variables.
The bulk density of WP and RCF samples reached their average values ranging from 40 to 80 kg/m’. It is generally known that cellulosic fibers are low bulk density, closed-air polymeric materials in a porous structure. Therefore, the bulk density is always lower than the density. Fig. 3 shows that bulk density increases with decreasing average fiber length in the studied range of variables. The calculated value of the correlation coefficient (0.7663) confirms a moderate dependence between both of the mentioned variables.
3.2.2 Dimensions and Morphology Study
3.2.2 Dimensions and Morphology Study
As shown in Tab. 2, the same values of the average width of the fibers in the samples (bleached wood pulp) were found (approximately 21-22 um), but the RCF samples are thicker (approximately 29-31 pm). The cause of this phenomenon is probably related to inorganic impurities. The heterogeneity in the fiber sizes is also reflected by the aspect ratio of the studied fiber samples. L/D ratio is in the range of 18.8-30.
As shown in Tab. 2, the same values of the average width of the fibers in the samples (bleached wood pulp) were found (approximately 21-22 um), but the RCF samples are thicker (approximately 29-31 pm). The cause of this phenomenon is probably related to inorganic impurities. The heterogeneity in the fiber sizes is also reflected by the aspect ratio of the studied fiber samples. L/D ratio is in the range of 18.8-30.
Figure 5: SEM micrographs of cellulosic fiber samples: WP (1-3) and RC (4-6); magnification = 1500x
Figure 5: SEM micrographs of cellulosic fiber samples: WP (1-3) and RC (4-6); magnification = 1500x
Table 3: Specific surface area and pores characteristics of Greencel cellulosic fibers (WP: 1-3; RCF: 4-6)
Table 3: Specific surface area and pores characteristics of Greencel cellulosic fibers (WP: 1-3; RCF: 4-6)
Figure 7: XRD diffractograms of WP fiber samples (1-3)
Figure 7: XRD diffractograms of WP fiber samples (1-3)
Table 4: Crystallinity index and crystallite size of Greencel cellulosic fibers (WP: 1-3; RCF: 4-6) 3.2.5 Degree of Cellulose Polymerization and Polydispersity Index
Table 4: Crystallinity index and crystallite size of Greencel cellulosic fibers (WP: 1-3; RCF: 4-6) 3.2.5 Degree of Cellulose Polymerization and Polydispersity Index
Table 5: Comparison of the values of the weight-average molecular weight (Mw), number-averag« molecular weight (Mn), polydispersity index (PDI) and degree of cellulose polymerization (DP) of WI and RCF samples Figure 9: Cellulose weight-molecular mass distribution of WP (a) and RCF (b) samples
Table 5: Comparison of the values of the weight-average molecular weight (Mw), number-averag« molecular weight (Mn), polydispersity index (PDI) and degree of cellulose polymerization (DP) of WI and RCF samples Figure 9: Cellulose weight-molecular mass distribution of WP (a) and RCF (b) samples
Figure 10: FTIR spectra of WP samples (1-3) in comparison to microcrystalline cellulose (MC)
Figure 10: FTIR spectra of WP samples (1-3) in comparison to microcrystalline cellulose (MC)
Thermal analysis provides information on the thermal stability of a material as well as heat release during simultaneous heating. The mass loss curves (TG), DTG and DSC curves of the six tested cellulosic fiber samples in an inert atmosphere of nitrogen are shown in Figs. 12-14. Tab. 5 summarizes the parameter values obtained from DSC analysis. As seen in Figs. 12-14, the thermal decomposition process of cellulosic fiber samples can be divided into three stages. As is known, the decomposition of cellulosic samples is a complex process involving a series of consecutive reactions. There were some difficulties in characterizing the decomposition behavior of substances forming cellulosic fiber samples and recognizing the progress of individual degradation actions occurring during their heating as a result of the complexity of its microstructure [25]. We have encountered a similar problem in the thermal degradation studying of organic compounds present in hemp hurds samples [52]. While only slight differences were observed between the samples in DTG curves during the course of the degradation (Figs. 13(a) and 13(b)), significant differences were found in the
Thermal analysis provides information on the thermal stability of a material as well as heat release during simultaneous heating. The mass loss curves (TG), DTG and DSC curves of the six tested cellulosic fiber samples in an inert atmosphere of nitrogen are shown in Figs. 12-14. Tab. 5 summarizes the parameter values obtained from DSC analysis. As seen in Figs. 12-14, the thermal decomposition process of cellulosic fiber samples can be divided into three stages. As is known, the decomposition of cellulosic samples is a complex process involving a series of consecutive reactions. There were some difficulties in characterizing the decomposition behavior of substances forming cellulosic fiber samples and recognizing the progress of individual degradation actions occurring during their heating as a result of the complexity of its microstructure [25]. We have encountered a similar problem in the thermal degradation studying of organic compounds present in hemp hurds samples [52]. While only slight differences were observed between the samples in DTG curves during the course of the degradation (Figs. 13(a) and 13(b)), significant differences were found in the
DSC curves (Figs. 14(a) and 14(b)). The TG, DSC, and DTG curves of the RC and WP fiber samples, obtained by analysis in a nitrogen atmosphere, s evaporation of physically adsorbed water (mois how a very weak initial endothermic peak between 25 and 27°C, where asmall weight loss (0.55-1.22 wt.%) was recorded. In this temperature range, the ure) from the fiber structure occurs. The moisture content in the samples determined gravimetrically ranged from 1.5 to 2 percent (Tab. 2). Owing to the hygroscopic nature of the fibers, the amount of moisture is highly dependent on the ambient humidity and he manner in which the fibers are handled [53] portion of the bound water in the fibers depends . Hemicelluloses and lignin constituting the major part of he amorphous phase play an important role in the storage of moisture in fibers. As shown in [54], a significantly on the crystallinity degree of the cellulose. In the second stage, the greatest mass loss between 206°C and 400°C was recorded due to the devolatilization process being the main decomposition process of cellulosic fiber samples. It has been widely accepted that the primary thermal decomposition of cellulosic materials occurs between 200°C and 400°C [55]. In this temperature range, the organic components are gradually released. Cellulose decomposition as an endothermic process in an inert atmosphere mostly starts in the amorphous regions [56]. The endothermic peak on the DSC curves (Figs. 14(a) and 14(b)) and one significant peak on the DTG curves (Figs. 13(a) and 13(b)) at a temperature of approximately 350°C is accompanied by a mass loss of 66.71, 78.62, 80.94 wt.% for WP (samples 1-3) and 48.45, 50.85, 56.13 wt.% for RCF (samples 4- 6). This mass loss is a result of the decomposition of the major components of the fibers. As demonstrated in [57], the temperature of the hemicellulose depolymerization ranged between 180°C and 350°C, but the decomposition of the largest portion of hemicelluloses occurred in the narrow temperature range of 180- 200°C. Cleavage of the glycosidic linkage of the cellulose units was observed between 275°C and 350°C [58]. The higher onset temperatures of cellulose decomposition (Tab. 5) indicate its higher thermal
DSC curves (Figs. 14(a) and 14(b)). The TG, DSC, and DTG curves of the RC and WP fiber samples, obtained by analysis in a nitrogen atmosphere, s evaporation of physically adsorbed water (mois how a very weak initial endothermic peak between 25 and 27°C, where asmall weight loss (0.55-1.22 wt.%) was recorded. In this temperature range, the ure) from the fiber structure occurs. The moisture content in the samples determined gravimetrically ranged from 1.5 to 2 percent (Tab. 2). Owing to the hygroscopic nature of the fibers, the amount of moisture is highly dependent on the ambient humidity and he manner in which the fibers are handled [53] portion of the bound water in the fibers depends . Hemicelluloses and lignin constituting the major part of he amorphous phase play an important role in the storage of moisture in fibers. As shown in [54], a significantly on the crystallinity degree of the cellulose. In the second stage, the greatest mass loss between 206°C and 400°C was recorded due to the devolatilization process being the main decomposition process of cellulosic fiber samples. It has been widely accepted that the primary thermal decomposition of cellulosic materials occurs between 200°C and 400°C [55]. In this temperature range, the organic components are gradually released. Cellulose decomposition as an endothermic process in an inert atmosphere mostly starts in the amorphous regions [56]. The endothermic peak on the DSC curves (Figs. 14(a) and 14(b)) and one significant peak on the DTG curves (Figs. 13(a) and 13(b)) at a temperature of approximately 350°C is accompanied by a mass loss of 66.71, 78.62, 80.94 wt.% for WP (samples 1-3) and 48.45, 50.85, 56.13 wt.% for RCF (samples 4- 6). This mass loss is a result of the decomposition of the major components of the fibers. As demonstrated in [57], the temperature of the hemicellulose depolymerization ranged between 180°C and 350°C, but the decomposition of the largest portion of hemicelluloses occurred in the narrow temperature range of 180- 200°C. Cleavage of the glycosidic linkage of the cellulose units was observed between 275°C and 350°C [58]. The higher onset temperatures of cellulose decomposition (Tab. 5) indicate its higher thermal
Table 5: Thermal parameters of cellulosic fiber samples (WP: 1-3; RCF: 4-6) obtained from DSC analysis Lignin degradation simultaneously proceeds with the decomposition of cellulose and hemicelluloses in the first and second temperature range, but its temperature range is broader than for the hollocellulose components. The decomposition of residual lignin starts at 160°C and slowly continues until its completed decomposition at 900°C [59]. stability in comparison to hemicelluloses in accordance with a previous paper [59]. According to work [60], higher cellulose resistance to a thermal treatment is probably due to the presence of a much higher amount of intra- and intermolecular hydrogen bonds between the cellulose chains, which can lead to more ordered and packed regions in the cellulose structure.
Table 5: Thermal parameters of cellulosic fiber samples (WP: 1-3; RCF: 4-6) obtained from DSC analysis Lignin degradation simultaneously proceeds with the decomposition of cellulose and hemicelluloses in the first and second temperature range, but its temperature range is broader than for the hollocellulose components. The decomposition of residual lignin starts at 160°C and slowly continues until its completed decomposition at 900°C [59]. stability in comparison to hemicelluloses in accordance with a previous paper [59]. According to work [60], higher cellulose resistance to a thermal treatment is probably due to the presence of a much higher amount of intra- and intermolecular hydrogen bonds between the cellulose chains, which can lead to more ordered and packed regions in the cellulose structure.
EE The values of the thermal conductivity, volume heat capacity and thermal diffusivity of the WP and RCF samples are introduced in Tab. 2. From a comparison of the thermal conductivities, it follows that nore favorable values have been achieved for the RCF samples (0.0595-0.0634 W/m.K) than for the WP samples (0.0644-0.0674 W/m.K). As is generally known, polymers consisting of monomers of organic compounds have low values of this parameter; the value of 0.062 W/m.K was obtained for the regenerated cellulose fibers (viscose kind) [63]. There are also visible the differences between the volume eat capacity and the thermal diffusivity of the studied samples (Tab. 2). As is known, thermal properties of cellulosic fibers are influenced by many factors. Variables influencing their thermal conductivity are the morphology, molecular structure, porosity, density, crystallinity degree, crystal orientation angle and mobility of molecular chains in amorphous regions [64]. The differences in the source quality of waste saper affect the thermal conductivity of cellulose fibers. Obviously, the effect of the cellulose content, crystallinity and degree of polymerization as well as the porous fiber structure is reflected in thermo ohysical characteristics of the cellulosic fibers, as shown in Figs. 15 and 16. Figure 15: Dependence of volume heat capacity on cellulose content (a) and crystallinity index (b) in Greencel fibers (WP: 1-3; RCF: 4-6)
EE The values of the thermal conductivity, volume heat capacity and thermal diffusivity of the WP and RCF samples are introduced in Tab. 2. From a comparison of the thermal conductivities, it follows that nore favorable values have been achieved for the RCF samples (0.0595-0.0634 W/m.K) than for the WP samples (0.0644-0.0674 W/m.K). As is generally known, polymers consisting of monomers of organic compounds have low values of this parameter; the value of 0.062 W/m.K was obtained for the regenerated cellulose fibers (viscose kind) [63]. There are also visible the differences between the volume eat capacity and the thermal diffusivity of the studied samples (Tab. 2). As is known, thermal properties of cellulosic fibers are influenced by many factors. Variables influencing their thermal conductivity are the morphology, molecular structure, porosity, density, crystallinity degree, crystal orientation angle and mobility of molecular chains in amorphous regions [64]. The differences in the source quality of waste saper affect the thermal conductivity of cellulose fibers. Obviously, the effect of the cellulose content, crystallinity and degree of polymerization as well as the porous fiber structure is reflected in thermo ohysical characteristics of the cellulosic fibers, as shown in Figs. 15 and 16. Figure 15: Dependence of volume heat capacity on cellulose content (a) and crystallinity index (b) in Greencel fibers (WP: 1-3; RCF: 4-6)
Figure 16: Dependence of thermal conductivity on degree of cellulose polymerization and HK total micro pore volume of Greencel fibers (WP: 1-3; RCF: 4-6)
Figure 16: Dependence of thermal conductivity on degree of cellulose polymerization and HK total micro pore volume of Greencel fibers (WP: 1-3; RCF: 4-6)
Table 6: Flexural and compressive strength of 28-day-cured WP and RC fiber-cement mortars Based on the measured values of the of capillary water absorption coefficient of 28-day-cured fiber- cement mortars, mortar sample with RCF (sample 2) reached a lower value of this parameter (0.23 kg/m’min°*) compared to mortar with WP fiber sample 5 (0.26 kg/m*min°*). This result also confirms the
Table 6: Flexural and compressive strength of 28-day-cured WP and RC fiber-cement mortars Based on the measured values of the of capillary water absorption coefficient of 28-day-cured fiber- cement mortars, mortar sample with RCF (sample 2) reached a lower value of this parameter (0.23 kg/m’min°*) compared to mortar with WP fiber sample 5 (0.26 kg/m*min°*). This result also confirms the
Testing the significance of a correlation coefficient based on comparing the calculated absolute and critical value for the linear dependences as shown in Figs. 15(a) and 16(b) showed that the calculated correlation coefficients (0.8764 and 0.9546, respectively) are approximately higher than the critical value of the correlation coefficient (0.8114) for a set of measured values at the selected significance level p = 0.05. There is a very strong dependence among the variables. The value of the correlation coefficient for the dependence of thermal conductivity on the degree of cellulose polymerization as shown in Fig. 16(a) was found to be lower (0.7833) than the critical value of the correlation coefficient but very close to this value. This result is related to a moderate dependence between both variables. The smallest force of statistical dependence expressed by the correlation coefficient (0.3700) was recorded between volume heat capacity and crystallinity index (Fig. 15(a)). Fig. 17 shows a very strong dependence (0.8828) between both variables. The waste paper cellulose fibers of lower quality contribute to a reduction in thermal conductivity values that can positively affect this parameter of fiber composite.
Testing the significance of a correlation coefficient based on comparing the calculated absolute and critical value for the linear dependences as shown in Figs. 15(a) and 16(b) showed that the calculated correlation coefficients (0.8764 and 0.9546, respectively) are approximately higher than the critical value of the correlation coefficient (0.8114) for a set of measured values at the selected significance level p = 0.05. There is a very strong dependence among the variables. The value of the correlation coefficient for the dependence of thermal conductivity on the degree of cellulose polymerization as shown in Fig. 16(a) was found to be lower (0.7833) than the critical value of the correlation coefficient but very close to this value. This result is related to a moderate dependence between both variables. The smallest force of statistical dependence expressed by the correlation coefficient (0.3700) was recorded between volume heat capacity and crystallinity index (Fig. 15(a)). Fig. 17 shows a very strong dependence (0.8828) between both variables. The waste paper cellulose fibers of lower quality contribute to a reduction in thermal conductivity values that can positively affect this parameter of fiber composite.