Impregnation of radiata pine wood by vacuum treatment II: effect of pre-steaming on wood structure and resin content

Radiata pine sapwood and heartwood were dried using high-temperature, conventional-temperature, and air drying schedules with and without pre-steaming. They were then impregnated by vacuum treatment with double-distilled water, toluidine blue, and fluorescein dye. For sapwood, there were only minor differences in uptake between drying methods and when pre-steaming was used. Using microscopy, the primary flow pathways in sapwood were found to be the resin canal network and ray parenchyma cells, which provided conduction without large resistance. In heartwood, uptake was strongly influenced by pre-steaming the green lumber. After pre-steaming heart-wood, there was an increase in uptake from all surfaces but especially from the radial surfaces. Lower extractive contents, disruption of epithelial and ray parenchyma cells, and alteration of the condition of bordered pits were also associated with pre-steaming. It was therefore possible to classify flow paths in radiata pine heartwood five ways, according to uptake values and wood anatomical features.This research was presented in part at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998.     

Studies on pre-treatment by compression for wood drying III: the reduction of moisture content,the recovery rate,and mechanical properties of wood compressed at different moisture content conditions

As a follow-up report, the pre-treatment by compression for wood drying was systematically studied in terms of the reduction of moisture content (MC), the recovery rate (RR), and mechanical properties of wood compressed at different MC conditions. The results showed that MC after compression on water-saturated wood determined the critical value of MC before compression which were about 84 and 105% at a compression ratio of 60 and 40% for Poplar and Chinese fir, respectively. Beyond the critical value, MC after compression remained constantly at about 84% and decreased slightly from 105% for Poplar and Chinese fir, respectively. The MC reduction decreased with the decrease of MC before compression. The MC reduction was rather effective when the MC before compression was higher than the critical value and was recommended to pre-treat for the effectiveness of MC reduction. In addition, after the recovery, the wood volume and mechanical properties were well retained for the wood compressed at all MC conditions which were above fiber saturation point (FSP) before and after compression. Therefore, the pre-treatment by compression is viable in terms of the RR and mechanical properties at rather broad MC conditions above FSP. Moreover, the compression force needed for treatment was almost same at these MC conditions.     

STUDY ON THE EFFECT OF WOOD MOISTURE CONTENT ON PERMEABILITY IN THE HYGROSCOPIC RANGE

Woodpermeabilityhascloserrelationshipwiththemanyfiledsofwoodworkingandusing,woodfluidpermeabi1-ityisrelatedtoinprocessingsuchaswooddrying;fireretartenttreatmen;pup1ingandpaper;woodpreservation.Theflowoffluidinwoodincludestwokindsoftransportprocess.Oneispenetrationfromwoodoutsidetoinside,suchas'woodpreservationandfireretartenttreatment,anotherisdiffusionfromwoodinsidetooutside'suchaswooddrying,Infact,woodpermeabilityinfulenceddirectlythequalityofwoodwaterheattreatment,Forthisreasontheresearchin…     

Methods for the determination of wood properties,Kraft pulp yield and wood fibre dimensions on small wood samples.

A trial set-up with methods for sampling, treatment and analysis of small wood chips are presented in this paper, to determine important wood and fibre properties, like basic density, dry density, volume swelling of wood, Kraft pulp yield, fibre length, fibre coarseness, fibre width, lumen width and fibre wall thickness. The required time for one sample is about 1.5 man-hour, but this requires relatively larger series and trained personnel. Acceptable measurement accuracy is achieved when the volume of the wood sample is at least 1.5 ml, except that of wood volume swelling. To gain acceptable measurement accuracy for volume swelling, the wood volume should be increased to at least 3 ml, and preferably more than 5–6 ml per sample. The level of pulp yield and wood density do not show a significant effect on the measurement accuracy for fibre cross-section dimensions. Fibre coarseness, on the other hand, has a significant influence on these accuracies. A double measurement of fibre coarseness will improve the accuracy to an acceptable level. The method presented here may, together with information about trees and growth locations, form the basis for greater insight into the mechanisms involved in development of wood and fibre properties in trees, which in turn may provide better control and utilisation of wood for pulp and paper production.Abbreviations CWD cell wall density in dry wood=1500 kg/m³ - Ww dry weight of wood (kg) - Vmax green (wet) volume of wood (m³) - Vmin dry volume of wood (m³) - BD basic wood density (kg/m³) - DD dry wood density (kg/m³) - VS maximum volume swelling of wood (%) - Wp dry weight of pulp (kg) - PY pulp yield (%) - C fibre coarseness, the average weight of a unit length of fibre (g/m) - CL average chip length (mm) - CWT average cell wall thickness (m) - FW average fibre width (m) - l average native fibre length in solid wood - L chip length - lc average fibre length in wood chip (mm) - Lc length-weighted fibre length in wood chip (mm) - lw native average fibre length in wood (mm) - Lw native length-weighted fibre length in wood (mm) - LW average lumen width (m) - llw average native fibre length, length weighted, in wood - X average fibre length in chip - Xlw average fibre length, length weighted, in chip     

Calcium accumulation in the wood of short-rotation cottonwood species: effects on pulp properties

We have found that kraft pulp handsheets, made from a number of hybrid poplar (Populus trichocarpa × Populus deltoides) clones, contain unusual surface deformations caused by vessel element mineral blockages. The blockages were composed mainly of calcium salt deposits that survived chemical pulping and beating processes. Our findings confirm that a natural process of accumulation of calcium salts occurs in certain poplar species. In this article, we describe the implications for the multi-use implementation of these poplars in short-rotation, intensive-culture plantations.     

Comparative study of Kenaf varieties and growing conditions and their effect on kraft pulp quality

Kenaf (Hibiscus cannabinus L.) is an annual plant which produces a very high fiber yield per hectare and has demonstrated to be a suitable material for pulping. The crop conditions influence fiber production, but there is no information about their effect on pulp quality. The aim of this work was to study the effect of kenaf varieties and crop conditions (watering dose and harvesting time) on sulfate pulp quality. The study has been made on bast fiber sulfate pulps due to their high added value. The quality criteria were fiber dimensions, chemical composition and pulp quality. Kenaf variety or crop conditions have significant effect on fiber dimensions, holocellulose content, kappa number and breaking strength. To obtain high fiber yield and good delignified pulps it is recommended to grow the Salvador variety and to employ advance harvesting. Received: 20 January 1999     

A method to determine lumen volume and collapse degree of pulp fibers by using bottleneck effect of mercury porosimetry

On applying mercury porosimetry to wood blocks or paper sheets, the “bottleneck” effect due to pits of fibers occurs and thus lumen volume can be determined from the weight increase due to the remaining mercury. However, in addition to the mercury in the lumen, some mercury drops may also remain in the space between fibers within a paper sheet. The mercury between fibers increased with an increase of basis weight. Thus, a large number of paper sheets of low basis weight, such as 10 g·m⁻², should be used to determine the lumen volume of pulp fibers. Furthermore, in the case of fibers from mechanical pulp with many open cut fibers, mercury can retract from the open lumen such that the bottleneck effect due to pits does not occur. Therefore, the degree to which fibers are cut should also be considered for lumen volume determination. Although quantitative estimation of open cut fibers is difficult, the percentage of open cut fibers is quite low for the long fiber fraction. Thus, the remaining mercury for the long fiber fraction can be adopted as the lumen volume at least for practical purposes. Compared with the original lumen volume of the wood, the volumetric degree of fiber collapse was also estimated. Plausible values of almost 100% for lightly beaten KP and about 85% for slabwood thermomechanical pulp were obtained for the degree of collapse. Part of this report was presented at the 56th Annual Meeting of the Japan Wood Research Society, Akita, August 2006     

Influence of wood moisture content and wood temperature on fungal decay in the field: observations in different micro-climates

In this study, Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) specimens were exposed in double layer field trials at four different exposure sites and under different exposure conditions (in total ten test sets). The material climate of wood in terms of wood moisture content (MC) and wood temperature was automatically monitored over a period of 6 years and compared with the progress of decay. The aim of this study was to highlight the interrelationship between microclimate, material climate, and decay as a basis for the establishment of dose-response functions to be used for service life prediction of wood and wood-based products. Differences in resulting decay dynamics between the test sites as well as between the different types of exposure were quantified and discussed with respect to corresponding microclimatic and material climatic conditions. The time between the beginning of exposure and the first occurrence of visible decay varied between the sites and influenced the total decay development. The fundamental importance of direct decay factors, such as MC and wood temperature, were underlined and basic requirements for establishing dose-response-functions to be used in service life prediction models were derived.     

Heat treatment of wet wood fiber: A study of the effect of reaction conditions on the formation of furfurals

Abstract

Furan monomers are produced when wood is heated at high temperatures. To understand the process conditions for production of furfural (FF) and hydroxymethylfurfural (HMF) from wood, samples of milled aspen wood were subjected to autohydrolyzis by microwave heating in a sealed Teflon reactor. The experiments were designed to simulate temperature and pressure variables of a fiberboard press and their effect on production of furans from the hemicelluloses that have the potential for promoting self-bonding of the wood fibers. The effect of a Lewis acid catalyst, AlCl₃·6H₂O on the formation of FF and HMF was also studied. The hydrolysates were analyzed for the liberated wood sugars and dehydration products, FF and HMF. The FF and HMF yields under autohydrolyzis conditions increased with increase in severity factor, CS. Under catalyzed hydrolyzis conditions, the FF yield decreased, while the HMF yield increased with increase in severity factor. Under catalyzed hydrolyzis conditions the FF yield decreased presumably due to degradation reactions including resin formation. The increase in HMF yield with increasing severity factor was most likely due to hydrolyzis of glucan from cellulose. These results suggest that FF and resin yields could be enhanced with the addition of a Lewis acid catalyst to the wood particles, but that process variables need to be controlled in order to avoid or minimize degradation of the wood cellulose.     

High-yield pulping of aspen wood: Relation between pulp properties and fibre characteristics by multiple linear regression

Summary High-yield pulps have been obtained by means of steam explosion pulping. This process was carried out as follows: 1) chips soak impregnation (60 °C, 24 h, L/C = 6) in solutions containing 8% Na₂SO₃ and a variable concentration of either Na₂CO₃ or NaHCO₃, ranging from 0 to 2%; 2) cooking at high temperature (190–200 °C) for short time (2-1 min); 3) rapid pressure release. This work shows that mechanical properties were substantially improved when adding a second chemical to the Na₂SO₃ impregnation solution. Moreover, refining energy requirement was significantly reduced. However, the higher chemical charge used made the optical properties drop. In this paper, mathematical models have been proposed in order to accurately predict specific refining energy and paper properties from sulfonate content and pulp yield. In addition, the relative importance of these two parameters has been studied.Thanks are due to the Natural Science and Engineering Council of Canada (NSERC) and Fonds pour la Formation de chercheurs et l'aide à la recherche of Quebec (FCAR) for their financial support.     

Influence of process variables on the properties of pulp and paper sheets obtained by sulphite pulping of olive tree wood

Summary A central composition design was developed to study the influence of process variables (temperature, pulping time, sulphite concentration, anthraquinone concentration and liquid/solid relation) on the properties of pulps (yield, holocellulose, α-cellulose and lignin contents, and brightness) and the paper sheets (stretch, burst index and tear index) obtained from them, in the sulphite pulping of olive tree wood. Equations that reproduce the properties of pulps prepared by sulphite pulping and of paper sheets obtained from it are reported. The proposed equations fit the experimental yield and the holocellulose and α-cellulose contents of the pulps with errors less than 5%, as well as brightness with errors less than 10%. Also, they reproduce the lignin content of the pulps, and the stretch, burst index and tear index of the paper sheets with errors less than 15%. Obtaining pulps with acceptably high yield, holocellulose and α-cellulose contents, and also a high brightness, in addition to low lignin contents, entails operating at a temperature of 193 °C for 143 min, using a sulphite concentration of 19.85%, an anthraquinone concentration of 0.1% and a liquid/solid relation of 6.24. These are also the most suitable conditions for obtaining paper sheets with a high stretch, burst index and tear index. Received 23 April 1998     

Long-term effect of wood and peat ash fertilization on nutrient content in peat and trees on a drained peatland

ABSTRACT

Total and soluble nutrients in peat were studied after ash fertilization on an oligotroph peatland in southeast Norway. Plots 15?m?×?15?m in size were fertilized with 0, 4, 7, and 10 tons ha¹ of wood or peat ash in 1944. Chemical analyses after 18, 35 and 48 years showed a gradual reduction of phosphorus (P) and calcium (Ca) from the 0 to 10?cm surface peat layer. Some of the leached Ca was recovered in the layers 10–20 and 20–40?cm, while hardly any of the lost P was recovered in this way. The amount of potassium (K) in the surface layer declined by 75% over the first 18 years, and remained stable thereafter. Nothing of the lost K was recovered in deeper layers. The pH reflected the Ca levels. Over the years, an increasing proportion of the applied P, K and Ca was retrieved in the trees. Needle analyses indicated that declining tree vigor on plots fertilized with 4 and 7 tons of ash ha^?1 was due to P limitations. After 48 years, the peat content of P and Ca was still significantly higher in fertilized than in control plots, thus demonstrating the long-lasting effect of ash fertilization.     

The effect of lignin on the bending properties and fixation by cooling of wood

To clarify the effects of lignin on the fixation of bending deformation by cooling, cooling set for delignified woods with various lignin residues were investigated to compare with mechanical and dynamic viscoelastic properties. Bending tests showed that steep reductions occurred in the modulus of elasticity and modulus of rupture with delignification during the initial stage of delignification. The dynamic viscoelastic measurements revealed that the peak temperature of tan δ due to micro-Brownian motion of lignin was reduced with delignification, and the peak disappeared in the temperature range of 5°–100°C for the specimens that had lost more than 21% of their weight. On the other hand, no clear change in residual set was found in the range of 0%–15% of weight loss in spite of a marked reduction in lignin content. Subsequently, set decreased steeply for the specimens delignified beyond 15% of weight loss. It was suggested that cooling set is not determined solely by lignin content but is influenced by changes in the quality of lignin due to delignification. Lignin quality affects the balance of the elastic potential to recover from deformation and its viscosity, which is an indication of resistance against flow. Part of this report was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

Evaluating the effect of drier and warmer conditions on water use by Quercus pyrenaica

Under climate change, severe and recurrent droughts can reduce forest production and cause widespread tree dieback. The response of different vegetation types to climate change can vary greatly and, therefore, must be individually assessed. This study was carried out in a Mediterranean oak forest (Quercus pyrenaica) subject to seasonal summer drought. To examine the response of the forest to the climate conditions predicted under climate change, a Soil–Vegetation–Atmosphere Transfer model [SPA, Williams, M., Rastetter, E.B., Fernandes, D.N., Goulden, M.L., Wofsy, S.C., Shaver, G.R., Melillo, J.M., Munger, J.W., Fan, S.M., Nadelhoffer, K.J. 1996. Modelling the soil-plant-atmosphere continuum in a Quercus–Acer stand at Harvard Forest: the regulation of stomatal conductance by light, nitrogen and soil/plant hydraulic properties. Plant, Cell, Environment 19, 911–927] was used. The model was parameterized using mostly local measurements (independent of the verification data) and tested against in situ sap flow measurements obtained during year 2007. The predictions of the model were broadly consistent with the observed dynamics of sap flow (the model explained 71% of the variance in daily transpiration and 75% of half-hourly sap flow), leaf water potentials and soil water content. Once the model had been validated, simulations were carried out under warmer and dryer conditions. Predicted warmer conditions (4 °C) caused a moderate increase in total simulated transpiration. Less frequent precipitation (40% longer dry periods between rainfall events) had very little effect on transpiration. In contrast, transpiration was reduced by 17% when the soil water reserves at the beginning of the summer were lower than in 2007, corresponding to those measured in a very dry year (2005). The reduction was exacerbated when changes in temperature and rainfall were also considered (up to 28% decline in transpiration). The higher atmospheric CO₂ concentrations (712 ppm) simulated together with climate change, did not prevent the decline in tree water use or soil water storage at the end of the summer. All scenarios caused the soil water storage to reach extremely low values at the end of the dry season (a minimum of 25 mm). It is concluded that climate change is likely to have a negative impact on tree water use and soil water resources in the study area, increasing the water deficit by as much as 30%.     

Poplar wood heat treatment: effect of air ventilation rate and initial moisture content on reaction kinetics,physical and mechanical properties

The kinetics of heat treatment as well as its effect on some physical and mechanical properties of poplar wood (Populus alba L.) were analysed in this research. Kinetic tests were performed at different treatment temperatures and two different air ventilation settings [low and high air exchange rate (AER) with the exterior]. The treatment kinetics was studied, starting from the oven-dry condition, according to the mass loss during time. The time–temperature equivalency was checked, the mass loss versus time formalised through a master curve. The analysis clearly showed how the heat treatment at low and high AER presents different degradation kinetics even if similar activation energy values were found. Some physical and mechanical properties of wood after treatments up to a mass loss of 7 and 10 % starting from oven-dry or standard environmental conditions state were also studied. All of the treated samples showed statistically significant differences compared to the untreated one. The treatments performed at 7 or 10 % of dry mass loss showed homogeneous behaviour. The same tendency was observed for the treatments starting at oven-dry or standard environmental conditions with the exception of Young’s modulus, which resulted in smaller reductions in wet starting condition when compared to dry samples.     

Wettability and the hysteresis effect in the sorption of water vapor by wood

Summary The hysteresis effect in the adsorption and desorption of water vapor by wood has been variously explained as a consequence of differences in (1) the availability of bonding sites for sorption on molecular surfaces, (2) the degree of aggregation of a swelling or shrinking cellulosic gel system, and (3) the wettability of submicroscopic capillaries within the cell wall.The wettability hysteresis of 28 tropical woods, calculated as the ratio of cosines of advancing and receding contact angles made by water, has been determined by the inclined plate method.For 13 of these species the availability of complete sorption isotherms permitted analysis by means of the Hailwood-Horrobin model to differentiate between monomolecular and polymolecular sorbed moisture. In the upper range of relative humidities, total sorption hysteresis is primarily the result of hysteresis in polymolecular sorption.Positive relationships found in this study between polymolecular sorption hysteresis and wettability hysteresis are consistent with the Kelvin equation with respect to the effect of varying contact angle and give at least partial support to Zsigmondy's explanation of hysteresis as a phenomenon of capillary condensation.Total sorption hysteresis for all 28 species in the upper range of relative humidities was also positively correlated with wettability hysteresis due to the predominant effect of polymolecular sorption hysteresis. It may be concluded that in the range of relative humidity above 60 percent, hysteresis shown by typical sigmoid isotherms is to a considerable degree a phenomenon of capillary condensation explainable by the Kelvin equation in its complete form including cosine of contact angle.

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Zusammenfassung Die Hysterese bei Adsorption und Desorption von Wasserdampf in Holz wird in der Regel als Folge von Unterschieden bei 1. der Zugänglichkeit von Bindungsstellen für die Sorption an molekulare Schichten, 2. des Aggregatzustandes eines quellenden oder schwindenden Cellulose-Gel-Systems und 3. der Benetzbarkeit der submikroskopischen Kapillaren innerhalb der Zellwand erklärt. Die Benetzbarkeits-Hysterese bei 28 tropischen Holzarten wurde durch das Verfahren mit geneigter Ebene bestimmt durch die Berechnung des Verhältnisses der cos-Werte des vorderen und hinteren Kontaktwinkels von Wasser.Bei 13 der geprüften Holzarten erlaubte das Vorhandensein der vollständigen Sorptionsisothermen eine Analyse mit Hilfe des Hailwood-Horrobin-Modells zur Unterscheidung zwischen monomolekular und polymolekular sorbierter Feuchtigkeit. In den höheren Bereichen der relativen Feuchtigkeit ist die Gesamtsorptionshysterese vorwiegend das Ergebnis der polymolekularen Sorption.Die in dieser Untersuchung gefundenen positiven Zusammenhänge zwischen der Hysterese der polymolekularen Sorption und der Benetzungshysterese stehen in Übereinstimmung mit der Kelvinschen Gleichung hinsichtlich des Einflusses des variierenden Kontaktwinkels und sie unterstützen, zumindest teilweise, die Theorie von Zsigmondy über die Hysterese als einer Erscheinung der Kapillar-Kondensation.Im oberen Bereich der relativen Feuchtigkeiten korrelierte die Gesamt-Sorptionshysterese für alle 28 Holzarten ebenfalls positiv mit der Benetzungshysterese infolge des überwiegenden Einflusses der polymolekularen Sorptionshysterese. Hieraus kann geschlossen werden, daß im Bereich der relativen Feuchtigkeit über 60% die Hysterese, die sich in einem typischen S-förmigen Verlauf der Sorptionsisothermen zeigt, zu einem wesentlichen Grade eine Erscheinung der Kapillarkondensation ist und durch die gesamte Kelvin-Gleichung, einschließlich des cos-Kontaktwinkels, erklärt werden kann.

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This research is part of a comprehensive study being conducted at the Yale School of Forestry in cooperation with the Office of Naval Research, U.S. Navy, under Contract No. 609(13), Project NR 330-001, Properties of Tropical Woods.     

The effect of elevated temperature exposure on the fracture toughness of solid wood and structural wood composites

Fracture toughness of wood and wood composites has traditionally been characterized by a stress intensity factor, an initiation strain energy release rate (G _init) or a total energy to fracture (G _f). These parameters provide incomplete fracture characterization for these materials because the toughness changes as the crack propagates. Thus, for materials such as wood, oriented strand board (OSB), plywood and laminated veneer lumber (LVL), it is essential to characterize the fracture properties during crack propagation by measuring a full crack resistant or R curve. This study used energy methods during crack propagation to measure full R curves and then compared the fracture properties of wood and various wood-based composites such as, OSB, LVL and plywood. The effect of exposure to elevated temperature on fracture properties of these materials was also studied. The steady-state energy release rate (G _SS) of wood was lower than that of wood composites such as LVL, plywood and OSB. The resin in wood composites provides them with a higher fracture toughness compared to solid lumber. Depending upon the internal structure of the material, the mode of failure also varied. With exposure to elevated temperatures, G _SS for all materials decreased while the failure mode remained the same. The scatter associated with conventional bond strength tests, such as internal bond and bond classification tests, renders any statistical comparison using those tests difficult. In contrast, fracture tests with R curve analysis may provide an improved tool for characterization of bond quality in wood composites.     

Acoustoelastic birefringence effect in wood II: influence of texture anisotropy on the polarization direction of shear wave in wood

Ultrasonic shear waves were propagated through the breadth direction of a wood beam which was subjected to a bending load such that it was in a plane-stress state. The oscillation direction of the shear waves with respect to the wood beam axis was varied by rotating an ultrasonic sensor, and the relationship between the shear wave velocity and the oscillation direction was examined. The results indicate that when the oscillation direction of the shear wave corresponds to the tangential direction of the wood beam, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. When the oscillation of the shear waves occurs in the anisotropic direction of the wood beam instead of in the direction of principal stress, the shear wave velocity exhibits a peak value. In addition, the polarization direction was found to correspond to the direction of anisotropy of the wood beam according to the theory of acoustoelastic birefringence with respect to plane stress. This indicates that when the acoustoelastic birefringence method is applied to stress measurement of wood, it is appropriate to align the oscillation direction of the shear wave with the principal axial direction of anisotropy in order to carry out ultrasonic measurement.     

The influence of pressure sum,fiber blend ratio,and basis weight on wet strength and dispersibility of wood pulp/Lyocell wetlaid/spunlace nonwovens

Wetlaid/spunlace(wetlace) nonwovens with sufficient wet strength in use and disintegration under flow field can be widely used in dispersible moist wipes. To achieve superior properties, wood pulp/Lyocell wetlace nonwovens at different process parameters including pressure sum (sum of each Jet Head pressure), Lyocell blend ratio, and basis weight were prepared. Meanwhile, the effects of these process parameters on the wet strength and dispersibility of materials were investigated. The results show that the wet strength of wood pulp/Lyocell wetlace nonwoven increases as the increase of process parameters. Pressure sum has positive linear relationship with material wet strength and exponential relationship with material dispersibility. When pressure sum is beyond 135 bars, material basis weight has significant influence on the dispersibility. Pressure sum of 210 bars is the key value that Lyocell content affects the material dispersibility. Overall, at the minimum pressure sum of 190 bars, wood pulp/Lyocell (60/40) wetlace nonwoven (80 g m^?2) has dispersion critical value with maximum wet strength.