Unbleached Pulp Research Articles

Effect of fiber drying on properties of lignin containing cellulose nanocrystals and nanofibrils produced through maleic acid hydrolysis

The effect of fiber drying on the properties of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) produced using concentrated maleic acid hydrolysis of a never dried unbleached mixed hardwood kraft pulp was evaluated. Two drying conditions, i.e., air drying and heat drying at 105 °C were employed. It was found that drying (both air and heat) enhanced acid hydrolysis to result in slightly improved LCNC yields and less entangled LCNF. This is perhaps due to the fact that drying modified the cellulose supermolecular structure to become more susceptible to acid hydrolysis and the enhanced hydrolysis severity at the fiber surface when using dried fibers. Drying substantially improved LCNC crystallinity and LCNF suspension viscoelastic behavior. The present study quantitatively elucidated the effect of pulp drying (either air or heat) on producing cellulose nanomaterials and has practical importance because commercial market pulp (heat dried) is most likely to be used commercially.

Mechanical fabrication of high-strength and redispersible wood nanofibers from unbleached groundwood pulp

In the past, the direct production of lignin-containing nanofibers from wood materials has been very limited, and nanoscale fibers (nanocelluloses) have been mainly isolated from chemically delignified, bleached cellulose pulp. In this study, we have introduced a newly adapted, heat-intensified disc nanogrinding process for the enhanced nanofibrillation of wood nanofibers (WNF) with a high lignin content (27.4 wt%). The WNF produced this way have many unique and intriguing properties in their naturally occurring form, for example, being able to be dispersed in ethanol and having ethanol solution viscosities higher than water solution viscosities. When WNF nanopapers were formed with ethanol, the properties of the nanofibers were recoverable without a notable decrease in the viscosity or mechanical strength after redispersing them in water. The preservation of lignin in the WNF was noticed as an increase in the water contact angles (89°), the rapid removal of water in the fabrication of the nanopapers, and the enhanced strength of the nanopapers when subjected to high pressure and heat. The nanopapers fabricated from the WNF were mechanically stable, having an elastic modulus of 6.2 GPa, a maximum stress of 103.4 MPa, and a maximum strain of 3.5%. Throughout the study, characteristics of the WNF were compared to those of the delignified and bleached reference cellulose nanofibers. We envision that the exciting characteristics of the WNF and their lower cost of production compared to that of bleached cellulose nanofibers may offer new opportunities for nanocellulose and biocomposite research.

Definition of optimal parameters for supercritical carbonation treatment of vegetable fiber-cement composites at a very early age

This paper presents a study of cellulose pulp fiber-cement composites subjected to supercritical carbonation at a very early age. The raw materials used for the creation of cementitious composite mixes include: Portland cement, limestone filler, and cellulose pulp. Composites were produced by a slurry vacuum dewatering process and subjected to curing conditions which studied the effect of supercritical carbonation concentration (0% and close to 100% of CO2), the effect of cellulosic pulp (unbleached or bleached), and durability. All samples were subjected to mechanical, physical, and microstructural tests. The initial period of thermal curing (varying from 24h to 48h) and exposure time to carbonation (from 1h to 2h), did not have a statistically significant effect on the mechanical performance of the composites. However, the flexural test results of carbonated composites reinforced with bleached pulp showed a statistically significant improvement when compared to unbleached pulp reinforcement (24% increased average modulus of rupture). Thus, for cementitious composites cured with supercritical carbonation, the use of bleached cellulosic pulp, 24h of thermal hydration and 1h in an environmental chamber provided the optimal curing conditions and the most desirable properties in this study.

The Use of Oil Palm Empty Fruit Bunches (OPEFB) Fibers as Partial Replacement for Imported Recycled Fibers

Papermaking in Malaysia is basically based on recycled (secondary) fibers which are sourced from various parts of the world with prices depending on the quality of the fibers procured. The costs of paper production could possibly be reduced by using local fibers as partial replacement provided that the strength requirements are not compromised; and one such type is the oil palm fibers which are obtained as the by-product of the palm oil industry. This paper reports the use of the oil palm empty fruit bunch (OPEFB) fiber as a partial substitute in the production of corrugating medium. Both unbleached and totally chlorine free (TCF) bleached OPEFB pulps were mixed in different ratios with high quality recycled pulps which had been mechanically and chemically treated. Burst strength results indicate as high as 70% recycled pulp can be replaced by OPEFB pulps yet still having strength properties that are comparable with the industrial produced corrugating medium. Although the effect of bleached pulp is significant at high addition levels of more than 70%, the cost-energy balance will not be effective to use these bleached fibers, and furthermore the utilization of unbleached pulps also gave the same desired results. The use of the underutilized OPEFB fibers for replacement of imported recycled fibers without compromising the paper strength qualities could help the Malaysian paper industry in their quest for finding fiber alternatives.

Determination of uronic acids and neutral carbohydrates in pulp and biomass by hydrolysis, reductive amination and HPAEC-UV

AbstractThe exact quantification of all carbohydrate constituents in wood and pulp is a challenge because of the various glycosidic linkages of the polysaccharides with different stabilities. The individual detector responses for the compounds in the hydrolysates additionally complicate the quantification as pure standards for 4-O-methyl-α-D-glucuronic acid (meGlcA) and related oligosaccharides are not commercially available for calibration. In the present paper, a new analytical procedure is presented, based on the reductive amination of the carbohydrates obtained via acidic and enzymatic hydrolysis of the polysaccharides before quantification by means of high performance anion exchange chromatography (HPAEC) and UV-detection. This approach was suitable for the analysis of neutral carbohydrates and uronic acids obtained via enzymatic hydrolysis from bleached pulps. In the case of unbleached pulps, the enzymatic hydrolysis was not complete and unhydrolyzed nano-scaled and micro-scaled particles remained in the hydrolysates as detected by dynamic light scattering (DLS) measurements. The new HPAEC-UV methodology was also applied to kraft pulps and a sulfite pulp; six different kinds of wood as well as wheat straw and bagasse. All relevant monosaccharides and the dimer of meGlcA and xylose could be detected in the hydrolysates. Accordingly, significantly higher yields of meGlcA were found compared to literature data.

EFFECTS OF TOTAL CHLORINE FREE (TCF) BLEACHING ON THE CHARACTERISTICS OF CHEMI MECHANICAL (CMP) PULP AND PAPER FROM MALAYSIAN DURIAN (DURIO ZIBETHINUS MURR.) RIND

The effects of bleaching process on the characteristics of pulp and paper produced from durian rind under chemi‑mechanical pulping (CMP) method were investigated. All process and characteristic tests were conducted according to Malaysian International Organisation for Standardization (MS ISO) and Technical Association of the Pulp and Paper Industry (TAPPI). Three (3) stages of peroxide (P‑P‑P) bleaching sequence through the Total Chlorine Free (TCF) bleaching process were applied to the unbeaten and unbleached durian rind CMP pulp. Bleached CMP durian rind pulp drainage time (32s) decreased (faster) and CSF freeness level (172.50ml) increased as compared to a control pulp. It was obtained that overall optical (brightness (66.36 %)) and mechanical characteristics (tensile index (38.33 Nm/g), tearing index (7.56 mN.m2/g), bursting index (2.42 kPa.m2/g), and number of folds (43)) of durian rind CMP 60 gsm paper sheet improved as the TCF bleaching process was applied to the unbleached CMP durian rind pulp.

Brightness stability of eucalyptus-dissolving pulps: effect of the bleaching sequence

AbstractThe factors governing the brightness reversion (BR) of dissolving pulps under heat exposure are investigated. Carbonyl (CO) groups were artificially introduced on fully bleached pulp by sodium hypochlorite (NaClO) oxidation. It was demonstrated that the CO groups are responsible for loss of brightness stability (BS). These groups were partly eliminated by an alkaline extraction stage (E), which improved BS. However, an alkaline peroxide stage (P) was more efficient than E to improve BS, but without any additional CO loss. Moreover, an unbleached dissolving pulp was bleached in the laboratory by elemental chlorine free (ECF) and totally chlorine free (TCF) [ozone-based] sequences to the same brightness. The very low CO content was about the same in both cases. The ECF-bleached pulp showed substantially lower BS than the TCF pulp. These results are interpreted such that the chemistry of chromophores in the unbleached pulp also governs BS.In situdetection of phenolic and quinone chromophores in bleached dissolving pulp was performed by electron paramagnetic resonance (EPR) spectroscopy and ultraviolet resonance Raman (UVRR) spectroscopy. The content of these groups was bleaching-sequence-dependent, which may be related to the BS differences.

Accumulation of sugar from pulp and xylitol from xylose by pyruvate decarboxylase-negative white-rot fungus Phlebia sp. MG-60

Phlebia sp. MG-60 is a white-rot fungus that produces ethanol with high efficiency from lignocellulosic biomass without additional enzymes. Through engineering of this powerful metabolic pathway for fermentation in Phlebia sp. MG-60, chemical compounds other than ethanol could be produced. Here, we demonstrate sugar accumulation from unbleached hardwood kraft pulp and conversion of xylose to xylitol by pyruvate decarboxylase (pdc)-negative Phlebia sp. MG-60. We isolated Phlebia sp. strain MG-60-P2 from protoplasts to unify the protoplast phenotypes of the regenerated strains. Homologous recombination achieved a stable pdc-knockout line, designated KO77. The KO77 line produced traces of ethanol, but accumulated xylitol from xylose or glucose from unbleached hardwood kraft pulp. These metabolic changes in the pdc-knockout strain reflect the potential of metabolic engineering in Phlebia sp. MG-60 for direct production of chemical compounds from lignocellulosic biomass.

The effect of pre-treatment on the production of lignocellulosic nanofibers and their application as a reinforcing agent in paper

In this work, three different lignocellulosic nanofibers (LCNF) were produced from unbleached wheat straw soda pulp by using different pre-treatments: mechanical, enzymatic, and TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl) oxy radical]-mediated oxidation processes. The different LCNF were characterized and studied by their chemical composition (FTIR), crystal structure (XRD), thermal degradation behaviour (TGA), morphological (TEM), and their reinforcement effect on papermaking slurries. The pre-treatment used to obtain LCNF showed significant differences on the nanofibrillation yield (37–95%), carboxyl content (74–362 µmol g−1), cationic demand (428–1116 µeq g−1), and on its dimensions (7–14 nm), thermal stability, and structure. Regarding application as reinforcement on papermaking slurries, LCNF obtained by TEMPO-mediated oxidation produced a greater reinforcing effect than the other LCNF. Nevertheless, the obtained LCNF from mechanical process produce a similar increase in the mechanical properties of the papersheets due to its high length, compared with LCNF obtained by TEMPO-mediated oxidation.

Integrated production of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) using an easily recyclable di-carboxylic acid

Here we demonstrate di-carboxylic acid hydrolysis for the integrated production of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) using two unbleached mixed hardwood chemical pulps of lignin contents of 3.9 and 17.2%. Acid hydrolysis experiments used maleic acid solution of 60wt% concentration at 120°C for 120min under ambient pressure. Yields of LCNC were low of less than 6% under this set of conditions. The higher lignin content sample produced LCNC with greater height (diameter) of 25nm but similar length of approximately 230nm to that from the lower lignin content fibers (height of 20nm). Interestingly, the higher lignin content sample resulted in LCNF with smaller height (diameter) of 7nm but longer length of >1μm, or greater aspect ratio than the LCNF from the lower lignin fibers of height 10nm and length <1μm. Lignin protected cellulose from esterification which resulted in LCNC and LCNF that was less carboxylated compared to those lignin-free CNC and CNF and therefore had lower charges. However, lignin is more hydrophobic and thermally stable than carbohydrates therefore LCNC and LCNF are favorable for composite applications.

INVESTIGATION AND ANALYSIS OF RECYCLING POTENTIAL OF FILTERING COMPOSITES BASED ON CELLULOSIC FIBRES RESULTED FROM THE INDUSTRIAL FILTRATION PROCESS OF ALIMENTARY LIQUIDS

&lt;p&gt;In this paper are presented some aspects related to recycling of material recovered from the waste fibrous filter composites, when obtaining some board grades with technical applications. Based on obtained results can be appreciated that the fibrous material from the waste filtering composites can be recovered in certain proportions to obtain of gypsum board grade used in building industry. It is emphasized that the quantity of fibrous material from waste filtering composites can be increased above 25%, maintaining of the same level of strength characteristics, both by utilization of dry strength agent and some quantity of virgin fibers (unbleached Kraft softwood pulp, TMP, pulp, etc.).&lt;/p&gt;

Mechanisms of the inhibition of enzymatic hydrolysis of waste pulp fibers by calcium carbonate and the influence of nonionic surfactant for mitigation.

Recycled paper mills produce large quantities of fibrous rejects and fines which are usually sent to landfills as solid waste. These cellulosic materials can be enzymatically hydrolyzed into sugars for the production of biofuels and biomaterials. Paper mill wastes also contain large amounts of calcium carbonate which inhibits cellulase activity. The calcium carbonate (30%, w/w) decreased 40-60% of sugar yield of unbleached softwood kraft pulp. The prime mechanisms for this are by pH variation, competitive and non-productive binding, and aggregation effect. Addition of acetic acid (pH adjustment) increased the sugar production from 19 to 22g/L of paper mill waste fibers. Strong affinity of enzyme-calcium carbonate decreased free enzyme in solution and hindered sugar production. Electrostatic and hydrogen bond interactions are mainly possible mechanism of enzyme-calcium carbonate adsorption. The application of the nonionic surfactant Tween 80 alleviated the non-productive binding of enzyme with the higher affinity on calcium carbonate. Dissociated calcium ion also inhibited the hydrolysis by aggregation of enzyme.

Adsorption Mechanism of Anionic Groups Found in Sulfonated Mulberry Stem Chemi-Mechanical Pulp (SCMP) for Removal of Methylene Blue Dye

The anionic groups (AGs) present in mulberry stem sulfonated chemi-mechanical pulp (SCMP) were studied relative to the adsorption of methylene blue (MB) dye. Adsorption isotherm experiments were carried out for the unbleached pulp, and for pulp that had been subjected to hydrogen peroxide (H2O2) bleaching. AGs present in the pulps appeared to govern the adsorption of MB. MB adsorption kinetics were evaluated for the bleached pulp. The methylene blue adsorption by SCMP, made from mulberry stems, conformed to the Langmuir adsorption model, which is consistent with a monolayer adsorption process. The adsorption thermodynamics showed that the adsorption process was spontaneous and exothermic. A pseudo-second order kinetic model described the adsorption mechanism of MB by the SCMP made from mulberry stems.

Steam explosion pretreatment used to remove hemicellulose to enhance the production of a eucalyptus organosolv dissolving pulp

The steam explosion (SE) pretreatment associated with the organosolv process was investigated to produce dissolving pulp from eucalyptus. Prehydrolysis Kraft (PHK) pulping was also done to produce viscose and acetate grade pulps as reference. The organosolv pulps were delignified in two steps with sodium chlorite. Viscose and acetate grade PHK pulps were bleached by OD0(EH)D1P and OD0(EP)D1PCCE sequences, respectively. Dilute acid-catalyzed (with acid addition) SE pretreatment dissolved more xylan than auto-catalyzed (no acid addition) SE pretreatment. Steam-exploded unbleached organosolv pulps showed lower residual lignin content and screened yield than unbleached organosolv pulps without SE pretreatment. Steam explosion pretreatment helped to decrease lignin content and damaged fiber length of unbleached organosolv pulps. The 1.0% H2SO4 organosolv pulp (organosolv dissolving pulp at bioconversion conditions) showed the highest reactivity. Even showing low viscosity for some applications, in general, the organosolv dissolving pulps produced in this study can be used for making lyocell fibers.

Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids

Here we demonstrate potentially low cost and green productions of high thermally stable and carboxylated cellulose nanocrystals (CNCs) and nanofibrils (CNF) from bleached eucalyptus pulp (BEP) and unbleached mixed hardwood kraft pulp (UMHP) fibers using highly recyclable dicarboxylic solid acids. Typical operating conditions were acid concentrations of 50 - 70 wt% at 100 °C for 60 min and 120 °C (no boiling at atmospheric pressure) for 120 min, for BEP and UMHP, respectively. The resultant CNCs have a higher thermal degradation temperature than their corresponding feed fibers and carboxylic acid group content from 0.2 - 0.4 mmol/g. The low strength (high pKa of 1.0 - 3.0) of organic acids also resulted in CNCs with both longer lengths of approximately 239 - 336 nm and higher crystallinity than CNCs produced using mineral acids. Cellulose loss to sugar was minimal. Fibrous cellulosic solid residue (FCSR) from the dicarboxylic acid hydrolysis was used to produce carboxylated CNFs through subsequent mechanical fibrillation with low energy input.

Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids.

Here we demonstrate potentially low cost and green productions of high thermally stable and carboxylated cellulose nanocrystals (CNCs) and nanofibrils (CNF) from bleached eucalyptus pulp (BEP) and unbleached mixed hardwood kraft pulp (UMHP) fibers using highly recyclable dicarboxylic solid acids. Typical operating conditions were acid concentrations of 50 - 70 wt% at 100 °C for 60 min and 120 °C (no boiling at atmospheric pressure) for 120 min, for BEP and UMHP, respectively. The resultant CNCs have a higher thermal degradation temperature than their corresponding feed fibers and carboxylic acid group content from 0.2 - 0.4 mmol/g. The low strength (high pKa of 1.0 - 3.0) of organic acids also resulted in CNCs with both longer lengths of approximately 239 - 336 nm and higher crystallinity than CNCs produced using mineral acids. Cellulose loss to sugar was minimal. Fibrous cellulosic solid residue (FCSR) from the dicarboxylic acid hydrolysis was used to produce carboxylated CNFs through subsequent mechanical fibrillation with low energy input.

Pulping and Bleaching of Hydro Distillation Waste of Citronella Grass (Cymbopogon winterianus Jowitt) for Papermaking

This investigation is aimed to explore the pulp and papermaking potential of solid residue left after isolation of essential oil from Cymbopogon winterianus Jowitt using hydro distillation, as well as to evaluate the physical strength properties of pulp and paper produced from it. Soda, soda–AQ (soda–anthraquinone) and kraft pulping of oil isolated C. winterianus were optimized and the corresponding optimum unbleached pulp in each process was subjected to environment friendly ECF (elemental chlorine free) bleaching using D1EpD2 (D = chlorine dioxide in acidic medium; Ep = alkaline extraction with addition of hydrogen peroxide; 1 and 2 = first and second time) sequence. Fibre morphological investigation and fibre classification of bleached pulp from every optimized pulping process were also carried out. Hand sheets of bleached pulps were prepared to evaluate the physical strength properties. All the methods were followed as per standard procedures. The proximate chemical composition of oil isolated C. winterianus revealed 62.70% holocellulose, 37.62% alpha-cellulose, 21.10% pentosans and 24.10% lignin. Kraft pulping at 12% NaOH dose and 20% sulphidity produced unbleached pulp with kappa 18.72, yield 43.68%, brightness 21.36% and viscosity 32.6 cp; while bleached pulp with brightness 83.67% and viscosity 16.7 cp. However, hand sheets prepared from soda–AQ pulping exhibited tensile index 31.5 N m/g, tear index 5.02 m Nm2/g and burst index 2.20 kPam2/g which were superior to kraft pulping. Soda pulp demonstrated inferiority in quality to kraft and soda–AQ pulps. No significant differences were observed in fibre morphology of pulps from different processes while fibre classification revealed maximum useful bleached fibres 55.9% from kraft pulping. This research proved that C. winterianus solid residue left after isolation of essential oil could be a substantial source for pulp and papermaking using conventional pulping processes and ECF bleaching sequence at process conditions described in this work.

Pulping and bleaching of Malaysian oil palm empty fruit bunches

Oil palm empty fruit bunch (EFB) was evaluated as a raw material for papermaking pulp production. The EFB was chopped, screened, and washed before cooking. Preliminary bench-scale trials were carried out using soda and soda-anthraquinone cooking followed by bleaching using elemental chlorine free and totally chlorine free sequences. Pilot-scale soda cooking was carried out in a 2300 L spherical digester using the soda process followed by a three-stage elemental chlorine free bleaching sequence. Unbleached and bleached EFB pulps were tested for physical and optical properties. Comparisons were made between the properties of the EFB pulps and bleached kraft eucalyptus pulp. The EFB unbleached and bleached pulps were acceptable for papermaking.

Influence of cellulose viscosity and residual lignin on water absorption of nanofibril films

The quality of cellulose nanofibril (CNF) films is affected by processing and raw material related factors. The causes of potential excessive cellulose degradation during defibrillation that may directly affect the quality of CNF films may be assessed by cellulose viscosity, which need further investigations. This study aims to investigate the influence of cellulose viscosity and residual lignin of four different hardwood species (Eucalyptus grandis - eucalyptus; Brosimum parinarioides - amapá; Parkia gigantocarpa - faveira; and Cordia goeldiana - freijó ) on water absorption of the subsequent CNF films. Viscosity of the unbleached and bleached pulps was measured by capillary viscosimetry after alkali and bleaching pre-treatments of the raw wood sawdust. Residual lignin was also determined for the bleached pulps. The films were obtained by casting method after pulp nanofibrillation through 10, 20, 30 and 40 passages in a mechanical defibrillator. The amount of water absorbed per film area (g/m2) after water immersion of the CNF films for 60 s was determined and normalized by the thickness. Overall, CNF films obtained from pulps with residual lignin and higher viscosity, and hence lower degradation by the alkali and bleaching pre-treatments, showed lower water absorption. The lowest water absorption of B. parinarioides CNF films may be highlighted. For pulps with lower viscosity, water absorption continuously increased with the increase of passages through the defibrillator, possibly due to combined degradation of pre-treatments and nanofibrillation. This tendency was observed from 10 to 40 passages for eucalyptus CNF films and from 10 to 30 passages for P. gigantocarpa CNF films.

Anionic wood nanofibers produced from unbleached mechanical pulp by highly efficient chemical modification

An easily produced deep eutectic solvent was used as an efficient reaction medium for the chemical modification of lignin-rich groundwood pulp to obtain highly charged anionic wood nanofibers.