Microstructural and chemical effects of wet/dry cycling on pulp fiber-cement composites

The microstructural and chemical mechanisms responsible for pulp fiber-cement composite degradation during wet/dry cycling are being investigated through environmental scanning electron microscopy (ESEM), energy dispersive spectroscopy (EDS), and mechanical testing. Based on these results, a three-part progressive degradation mechanism for cast-in-place kraft pulp fiber-cement composites is proposed, which involves: (1) initial fiber-cement or fiber interlayer debonding, (2) reprecipitation of needle-like or sheath-like ettringite within the void space at the former fiber-cement interface or between the S1 and S2 fiber layers, and (3) fiber mineralization due to reprecipitation of calcium hydroxide filling the spaces within the fiber cell wall structure. This investigation also revealed that kraft pulp fibers exhibit poor resistance to degradation due to their inferior dimensional stability, as compared to thermomechanical pulp (TMP) fibers. TMP fibers contain significant amounts of lignin, which is alkali sensitive. Despite this, TMP fiber-cement composite exhibit improved resistance to degradation during wet/dry cycling. It is proposed that this improvement in durability may be attributed to the presence of lignin in the cell wall restricting fiber dimensional changes during wetting and drying, and hence, minimizing fiber-cement debonding. Additionally, it is proposed that lignin acts as physical barrier to calcium hydroxide formation within the fiber cell wall, minimizing fiber mineralization of TMP fibers.     

Wood fiber surface treatment level effects on selected mechanical properties of wood fiber-cement composites

The objective of this study was to determine the effects of sodium (N) silicate, potassium (K) silicate, and silane (Si) treatment levels on newspaper and unbleached kraft fibers for enhancing selected mechanical properties of wood fiber-cement composites compared to untreated wood fiber-cement composites. Both wood fiber types were treated with selected aqueous solution strengths, air dried, and mixed with water and cement. The bending and compression properties of the specimens were determined after 28 days of hydration. Results of this study indicated that the aqueous chemical treatments of the wood fibers enhanced some of the mechanical properties of wood fiber-cement composites compared to the untreated wood fiber-cement composites. The enhancement depended on chemical treatment and wood fiber type. All three chemical treatments of newspaper fiber enhanced the normalized toughness values compared to the untreated newspaper fiber-cement composites. In addition, higher treatment levels using N silicate with newspaper fiber improved the compressive strength and bending modulus of the composites compared to the untreated newspaper fiber-cement composites. Kraft fiber treated with all three chemicals enhanced the compressive strength, bending modulus and bending strength compared to the untreated kraft fiber-cement composites. However, only silane-treated kraft fiber improved the normalized toughness values compared to the untreated kraft fiber-cement composites. The results of the study indicated that certain chemical treatments react better with different wood fiber types resulting in selected mechanical property enhancements.     

Supplementary cementitious materials for mitigating degradation of kraft pulp fiber-cement composites

Kraft pulp fiber reinforced cement-based materials are being increasingly used where performance after exposure to environmental conditions must be ensured. However, significant losses in mechanical performance due to wet/dry cycling have been observed in these composites, when portland cement is the only cementitious material used in the matrix. In this research program, the effects of partial portland cement replacement with various supplementary cementitious materials were investigated. Binary, ternary, and quaternary blends of silica fume, slag, Class C fly ash, Class F fly ash, metakaolin, and diatomaceous earth/volcanic ash blends were examined for their effect on the degradation of kraft pulp fiber-cement composite mechanical properties (i.e., strength and toughness) during wet/dry cycling. After 25 wet/dry cycles, it was shown that binary composites containing 90% slag, 30% metakaolin, or greater than 30% silica fume did not exhibit any signs of degradation, as measured through mechanical testing and microscopy. Ternary blends containing 70% slag/10% metakaolin or 70% slag/10% silica fume were also effective in preventing degradation. A reduction in calcium hydroxide content and the stability of the alkali content due to supplementary cementitious material addition were shown to be primary mechanisms for improved durability.     

Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

This article focuses on the effect of pulp bleaching and emerging commercial compatibilizers on physical performance of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. Industrially bleached and unbleached hardwood kraft pulp fibers are treated with several additive types, and compounded with PLA to fiber content of 30 wt %. After injection molding, the produced biocomposites are evaluated by their mechanical performance and fiber–matrix adhesion. For selected materials, fiber surface and fiber properties are reflected to composite performance by analyzing the compositions, dimensions, and lignin coverage of original fibers, as well as fiber dispersion and dimensions after melt processing. As a conclusion, unbleached kraft pulp fibers provide significant improvement in physical properties of PLA/pulp fiber composites. Of the screened compatibilizers, epoxidated linseed oil has a clear positive effect on performance when bleached kraft pulp fibers are used. The improvements correspond to enhanced fiber–matrix adhesion and differences in remaining fiber length distributions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47955.     

The Effect of Fiber Surface Lignin on Interfiber Bonding

Abstract

It has been speculated in several studies that lignin would impair interfiber bonding when present on the fiber surface due to the hydrophobic nature of lignin. Several experiments were devised in the present study to compare the internal bond strength and specific bond strength of pulp fibers with different surface lignin concentrations. The pulp samples used included unbleached and fully bleached kraft pulp, CTMP pulp with different middle lamella coverage on the fibers, and fully bleached pulp with lignin adsorbed on the fiber surface. With all of the pulp samples used, the internal bond strength was reduced markedly when lignin was present on the fiber surface; but the relative bonded area was not affected significantly.     

Wood fibers as reinforcing fillers for polyolefins

Wood pulp fibers possess strength and modulus properties which compare favorably with glass fibers when the differences in fiber densities are considered. Softwood pulp fibers with fiber aspect ratios near 100 are readily dispersed into high-density polyethylene or isotactic polypropylene with the aid of carboxyic dispersing agents to form mixtures containing 50 weight-percent wood pulp which can be readily injection molded. The mechanical properties of the molded specimens were similar for all types of pulp including Kraft (bleached and unbleached), mechanical and chemical-mechanical pulps, waste pulps, and reclaim newspapers. Comparisons of the stiffness/weight efficiencies revealed that pulp composites equal or exceed the stiffness of most traditional materials of construction including steel, aluminum, glass-fiber composites, and talefilled polyolefins, while retaining a major material cost advantage. The measured strength values of the pulp composites were less than the theoretically predicted values due to the presence of voids created by the formation of volatiles during processing. Mechanical pulps which were available in dry form were preferred because of lower cost and ease of handling. Wood fibers are non-abrasive so that relatively large concentrations may be incorporated into polyolefins without causing serious machine wear during mixing and fabrication.     

黄麻与聚乙烯醇纤维增强水泥土的弯曲及早期抗裂性能

深层水泥土搅拌桩围护墙具有水泥基材料的特性,包括脆性破坏以及较低的拉伸强度和弯曲强度,且温度应力产生的干燥收缩可能会导致裂缝的产生并引起墙体渗漏和塌陷。本文研究了黄麻纤维和聚乙烯醇(PVA)纤维增强水泥土搅拌桩的弯曲性能和裂后性能,并对纤维改善水泥土早期干缩裂缝的效果进行了对比。结果表明,随着黄麻纤维和PVA纤维含量的增加,第一裂缝弯曲强度和峰值弯曲强度均逐渐增加。纤维对改善水泥土的裂后性能起着至关重要的作用,水泥土残余弯曲强度比、延性指数和韧性随纤维含量增加显著提高。黄麻纤维在韧性方面的表现略好于PVA纤维,在其他裂后指标上两种纤维差距较小。采用数字图像相关方法研究纤维对水泥土早期塑性收缩裂缝的影响,结果表明,水泥土中添加纤维可有效抑制干燥条件下收缩裂缝的形成和扩展,纤维的掺入有效减小了水泥土干缩裂缝的宽度和数量,且纤维含量越多效果越佳。     

Use of wood fibers in thermoplastics. VII. The effect of coupling agents in polyethylene–wood fiber composites

Linear low density polyethylene (LLDPE) was reinforced with different wood fibers, aspen chemithermomechanical pulp (bleached and unbleached), and other commerical wood pulps. Silane coupling agents A-172, A-174, A-1100, and polymethylene polyphenyl isocyanate were used to improve the bonding between the fiber and matrix. LLDPE filled with pretreated wood fiber produced a significant improvement in tensile strength and modulus. Comparison of tensile and impact properties of wood fiber composites with mica and glass fiber composites shows the potential advantage (in terms of material cost and specific properties) of wood fiber as a reinforcement.     

COMPARISON OF ION EXCHANGE AND DONNAN EQUILIBRIUM MODELS FOR THE PH-DEPENDENT ADSORPTION OF SODIUM AND CALCIUM IONS ONTO KRAFT WOOD PULP FIBERS

ABSTRACT

Management of nonprocess element (NPE) accumulation in pulp washing operations requires equilibrium models that predict the distribution of metals between the wash liquor and the pulp fibers. The overall goal of this study was to assess models for predicting the multi-component adsorption of hydrogen ions (H⁺), sodium ions (Na⁺), and calcium ions (Ca⁺²) onto bleached and unbleached kraft pulp fibers over a pH range of 2.7–11. As part of this study, binary equilibrium constants for hydrogen and metal ion exchange on carboxylate sites in bleached pulp (0.041 meq/g dry pulp) were measured at 25°C, with log K ^Na/Ca = ?1.604 ± 0.119, log K ^H/Ca = 0.633 ± 0.087, and intrinsic dissociation constant pK _io of 3.64 ± 0.46. Ion exchange and Donnan equilibrium models adequately predicted the multi-component equilibrium data for competitive adsorption of H⁺, Na⁺, and Ca⁺² onto bleached kraft wood pulp fibers. The ion exchange model was fully predictive, whereas the Donnan model required that the solution pH be known. At pH 2.7–6, the Donnan model predicted the adsorption of Na⁺ and Ca⁺² onto both bleached and unbleached wood pulp fibers better than the ion exchange model. The ion exchange model assumed that residual carboxylate in the pulp served as the only site for the competitive binding of hydrogen and metal ions. In contrast, the Donnan model assumed a non site-specific distribution of metal ions between charged fiber and external solution phases and a carboxylate site specific adsorption of hydrogen ions. Above pH 6, both models failed to predict that the calcium adsorption on unbleached brownstock pulp increased beyond the carboxylate site capacity, suggesting that other functional groups within the brownstock pulp with intrinsic dissociation constant values higher than carboxylate were providing additional binding sites for calcium.     

The Use of Ozone or Oxygen in The First Bleaching Stage

An ODED or a ZEDED sequence bleached kraft hardwood and softwood pulps to 87 — 89‰ ISO brightness. The bleached yields were similar for a given pulp, whether oxygen or ozone was used in the first stage. The strength properties of the fully bleached pulps were essentially the same as those of the unbleached pulps. The COD and colour values of the effluents after ozone delignification and subsequent extraction were 25‰ and 60‰ lower, respectively, than those of the effluents after an oxygen treatment.     

Radiation grafting of vinyl monomers onto wood pulp cellulose. II

The effect of radiation dose rate and beating time on the mutual radiation grafting of styrene to unbleached and bleached kraft wood pulp was studied. Companion studies on the effect of beating time, peroxidation grafting, and order of monomer addition on the preirradiation graft copolymerization of acrylamide and diethylaminoethyl methacrylate were conducted on bleached wood pulp. The grafting rate of styrene increased with dose rate, but the kinetics suggests a significant diffusional resistance to the observed grafting rate. The per cent graft measured at fixed grafting conditions decreased markedly as pulp beating (effected prior to grafting) was increased. It is suggested that the decrease in grafting with beating is due to an increase in the accessibility and swelling of the beaten fibers. Dimethylaminoethyl methacrylate appeared to inhibit the grafting of acrylamide, and double grafting had to be used to graft both hydrophilic polymers to the pulp. The mechanical properties of high-yield pulp and groundwood were improved by the addition of the grafted pulps. The double grafts appeared to show promise as fibrous beaten additives for dry strength improvement. The styrenegrafted pulps were found not to respond at all to the beating process.     

High Stiffness Natural Fiber‐Reinforced Hybrid Polypropylene Composites

Abstract

Natural fibers are potentially a high‐performance non‐abrasive reinforcing fiber source. In this study, pulp fibers [including bleached Kraft pulp (BKP) and thermomechanical pulp (TMP)], hemp, flax, and wood flour were used for reinforcing in polypropylene (PP) composite. The results show that pulp fibers, in particular, TMP‐reinforced PP has the highest tensile strength, possibly because pulp fibers were subjected to less severe shortening during compounding, compared to hemp and flax fiber bundles. Maleic‐anhydride grafted PP (MAPP) with high maleic anhydride groups and high molecular weight was more effective in improving strength properties of PP composite as a compatiblizer. Coupled with 10% glass fiber, 40% TMP reinforced PP had a tensile strength of 70 MPa and a specific tensile strength comparable to glass fiber reinforced PP. Thermomechanical pulp was more effective in reinforcing than BKP. X‐ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used to aid in the analysis. Polypropylene with high impact strength was also used in compounding to improve the low‐impact strength prevalent in natural fiber‐reinforced PP from injection molding.     

Characterization of kraft pulp delignification using sodium dithionite as bleaching agent

Abstract

The delignification of kraft pulp with sodium dithionite was studied to remove lignin content in the pulp. The sodium dithionite dissolves the chromophoric groups and residual lignin present in the pulp. The increase in dosage of sodium dithionite and reaction temperature of delignification has positive effect on kappa reduction of pulp. X ray diffraction was used to determine the crystallinity index of bleached pulp. The crystallinity increased from 83.3% for unbleached pulp to 86.7% after delignification. Fourier transform infrared spectroscopy shows the reduction in hydrogen bonding in bleached pulp and also the conversion of cellulose I to cellulose II. FT-Raman spectra shows that the fluorescence observed in the spectra of unbleached pulp reduced significantly in comparison to the spectra of bleached pulp resulting in removal of residual lignin and chromophoric groups present in the pulp. Scanning electron imaging shows the smoothening of fiber surface after bleaching. The delignification reaction followed first-order kinetics and activation energy is 33.57kJ/mol.     

Infrared Absorption Spectra of Cellulose Pulps of Palm Tree

Palm leaves are used for the production of different cellulose pulps; their properties are investigated, the resulting pulps were bleached by a multistage process, the effects of the addition of solvent during the pulping process on the chemical structure of the pulps are discussed. The strength properties of the paper which is produced from unbleached and bleached pulps increased with increasing cellulose percentage and decreasing lignin content in the pulp. Infrared absorption spectra were recorded for different unbleached and bleached pulp in the frequency range 200–4000 cm^-1 by using the alkali halide disk technique; the factors which affect the experimental technique were calibrated through these studies. The structural units within pulping yield (holocellulose, hemicellulose, cellulose, lignin, and ash) were interpreted within the pulp network structure by the infrared absorption spectra, where different samples of unbleached, bleached soda, and kraft pulps were also elucidated by IR spectra, after preheating at different temperatures and with using different ratios of organic solvents. The addition of organic solvents decreased or increased the crystallinity indices, depending on the type of solvent and the pulping temperature. It was also found that, at the same pulping temperature (155°C) and with the same percent of organic solvents in the pulping liquor, the asymmetry indices also the mean hydrogen bonding strength (A _OH/A_CH) of the unbleached soda pulps (organosolv or nonorganosolv pulping) were less than that of unbleached kraft pulps, except for the pulps obtained by pulping with dioxan at 155°C. The mean hydrogen bond strength of the bleached pulps decreased or increased, depending on the type solvent used and the pulping temperature.     

Production and Characterization of Cellulose Nanofibrils from Different Chemical and Mechanical Pulps

In this study, mechanical fibrillation for the production of cellulose nanofibrils (CNF) from chemical and mechanical pulps with different chemical compositions was studied. To investigate the effect of nanofibrillation on wood pulps by the grinder, the nanofibrils obtained from grinded pulp were characterized with morphology, particle size distribution, apparent viscosity in aqueous solution, degree of crystallinity, and water retention capacity. The results showed that the low lignin-containing unbleached kraft pulp (UKP) exhibited good performance for fibrillation, resulting in CNF with high viscosity, high water retention value, and small particle size. However, the fibrillation of high lignin-containing chemi-thermomechanical pulp was the most inefficient which resulted in heterogeneous materials with relatively low viscosity, low water retention value, and large particle size compared to chemical pulps. Furthermore, bleached softwood pulp from radiata pine was found to be much faster and for easier fibrillation compared to the bleached hardwood pulp from acacia due to the more rigid structure of hardwood fibers.     

Dissolved Lignin and Other Aromatic Substances in Thermomechanical Pulp Waters

Abstract

Dissolved aromatic substances in water suspensions of unbleached and peroxide‐bleached spruce thermomechanical pulp (TMP) were isolated by sorption on XAD‐8 resin and fractionated into lignin and oligomeric aromatic substances (OAS). The fractions were characterized by chromatographic (GC and HP‐SEC) and spectrometric (FT‐IR, ¹³C‐NMR, GC‐MS) methods, as well as by GC after direct on‐line pyrolysis and thermally assisted hydrolysis and methylation. The dissolved lignin in unbleached TMP water was structurally similar to spruce milled‐wood lignin (MWL), but its average molar‐mass was lower and the mass distribution more narrow. The oligomeric aromatic substances included phenolic dimers, trimers, and tetramers that were structurally different from those of MWL. After peroxide bleaching the amount of dissolved semipolar (MTBE) extractives and oligomeric aromatic substances was much lower. The amount of dissolved lignin from wood fibers was, on the contrary, much higher. The lignin released from TMP after bleaching was extensively oxidized and had a slightly higher average molar‐mass than lignin released from unbleached TMP.     

Biocatalytic conversion of kraft pulp using cellulase complex of <Emphasis Type="Italic">Penicillium verruculosum</Emphasis>

The efficiency of biocatalysts based on the cellulase complex from the Penicillium verruculosum fungus in the hydrolysis of kraft pulp from soft and hardwood is investigated. The activities of biocatalysts with respect to unbleached and bleached cellulose samples and the dependence of the degree of cellulose conversion on the content of noncellulose components are determined. It is shown that wet kraft pulp exhibits high reactivity in enzymatic hydrolysis with cellulase complex from P. verruculosum and is undoubtedly of interest as a substrate for scaling up biotechnological processes of the bioconversion of renewable plant-derived materials.     

The utilization of thermomechanical pulp fibers in WPC: A review

Thermomechanical pulp (TMP), among other natural fibers, features characteristics that make it a promising candidate for the utilization in polymer composites. This review is providing an overview on the current state of research on TMP reinforced polymer composites. More than 50 references were reviewed. The cited literature is catalogued according to pretreatments, batch or continuous procedures, processing at laboratory or industrial scale, fiber contents, polymer types, coupling agents as well as wood species. The reinforcing potential of TMP utilized in composites is demonstrated. Tensile strength was found to be peaking at a fiber content of around 40 wt %. Fiber morphology is presumed to be an important determinator for composite properties. Specific mechanical energy [kWh/kg] is presented as an indicator suitable to compare the influence of various processes on fiber morphology. Furthermore, the feed‐in and dosing issue that generally accompanies the utilization of cellulosic fibers is described and possible solutions are discussed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45161.     

漆酶对未漂马尾松磨木浆的酶法改性

利用NS51002和NS51003漆酶/介体分别对马尾松未漂磨石磨木浆(GP)进行生物酶处理及后续的H2O2漂白,并对酶处理浆漂白前后的白度和强度性能进行测定。研究结果表明,利用漆酶NS51003处理马尾松未漂GP,可有效提高纸浆的白度及强度性能,而且酶处理后纸浆具有更好的可漂性,并且经过H2O2漂白后的酶处理浆亦具有更高的白度和更好的强度性能;而漆酶NS51002漆酶/介体对纸浆的改性效果甚微。     

Properties of Isoprene Rubber Reinforced with Treated Bleached Kraft Cellulosic Fibers or Rayon Fibers

Abstract

Both native and regenerated (rayon) cellulosic fibers are potential reinforcing elements in rubbers due to their relatively good mechanical properties, suitable aspect ratio, low cost and low density. The properties of the cellulosic fibers can also be changed fairly easily by chemical treatment. The effects of two treatments, mercerization (NaOH-immersion) and benzylation, on the mechanical properties of a rubber-cellulose composite are here reported. The rubber matrix was isoprene and the fiber content 20% by volume (27% by weight). Mercerization of bleached kraft fibers gave a composite with a higher modulus and strength than was attained when untreated kraft fibers were used, whereas benzylation of both kraft fibers and rayon fibers caused a reduction in the strength and stiffness of the rubber composites. This is interpreted as being due to a decrease in the degree of interaction between the cellulose fiber and the matrix due to the benzylation. The effect of these treatments on the mechanical properties of single rayon fibers is also reported.