THIN LIGNOCELLULOSIC LINERS BASED OF SPRUCE SHAVINGS

The article is devoted to determining the basic physical and mechanical properties of sheet materials up to 1.5 mm thick based on wood shavings and PVAc glue with a high proportion of water, pressed under high pressure up to 25 MPa and a temperature of around 190°C, so that the softening of lignin caused by the generated steam, allow to create a compact and non-crumbling surface. In order to characterize the physical-mechanical properties of the new wood-based sheet material with minimum thickness and characteristic elasticity, tests according to the CEPI (Confederation of European Paper Industries) standards were adopted. Procedures for tensile strength according to ISO 1924-2 (2008), Burst strength according to ISO 2758 (2014), puncture according to ASTM D781-68 (1973), water absorption according to ISO 5637 (1989) and porosity according to TAPPI Test method T460 were applied

Technology of Particleboard’s Preparation by Cold Pressing after Hot Mat Compression

The article describes a method of preparing particleboards (PB) from fresh and recycled chips by a new technology of cold pressing after hot compression of the mat according to PCT/SK2023/000007 (ÚPV SR, 13.06.2023) using polyvinyl acetate (PVAc) glue. For comparison, the experiment was also carried out using urea formaldehyde (UF) glue and their mutual combination. The new method shortens hot pressing, or causes reduction of pressing temperatures, while the prepared PB released from pressure no longer spring and cure over time. The curing kinetics of both PVAc and UF adhesives were described by monitoring the flexural strength and modulus of elasticity of PB as a function of time after release of pressure.
Modeling of the PB pressing process based on PVAc glue, which consists of overheating the pressed cross-section of the board to 90°C and its subsequent cooling to a temperature when the board is already stable, i.e. below a temperature of 70°C, was carried out using of a hot and cold press, while the pressing cycle lasted 140 s. Shortening the pressing cycle to 100 s was achieved by applying the glue to the chips already preheated to 92°C. Laboratory tests have confirmed that the mechanical properties of PB are in accordance with the requirements of EN 312/3 for chipboards for interior conditions, including furniture, for use in dry environments.

Water retention of beech shavings heat-treated at lower temperatures

Water retention after 2 hours and 24 hours of soaking in water was determined for beech shavings subjected to heat treatment at temperatures of 120°C, 140°C and 160°C for 2 hours, 4 hours, 6 hours and 8 hours in order to reduce the equilibrium moisture content (EMC) of the wood shavings for use in wood based composites. EMC was determined after 14 days of air conditioning at 23°C and 55% relative humidity. The measured values were compared with the sample dried at 103°C. Water retention was determined after 15 min of centrifugation at 1400 rev.min-1 for a more objective assessment of the wood’s ability to retain water in the cell lumens. The results showed that heat treatment reduces the EMC of beech shavings heat-treated at 160°C for 8 hours in the given conditions from 8.7% to 6.19%. The reduction of EMC at lower temperature was not sufficient enough, especially in the shorter treatment duration of up to 6 hours. In parallel, the reduction of water retention from 65.53% to 47.79% was caused by heat treatment for 8 hours at 160°C.

Chemical processing of waste wood based agglomerates Part I: Evaluation of properties of fluting liners made of semichemical pulp obtained by a mildly alkaline sulphur-free cooking process

The article describes the method of evaluation and preparation of fluting liners produced from semichemical pulp of waste wood particle boards (PB) and oriented strand boards (OSB) and after the combination with old corrugated cardboards (OCC) to improve strength properties. The semichemical pulp was obtained by a mildly alkaline boiling process from two fractions of waste PB and OSB. Properties as thickness, bulk density, gurley, tensile strength, tensile index, breaking length, burst index, CMT30 and SCT were monitored on lab sheets 127 g.m-2 and 170 g.m-2. Values of pH and residual NaOH and Na2CO3 were determined in batch leachate.

Possibilities of removing condensate from a heat recovery unit utilizable in paper industry

Methods, processes and equipments currently used for heat recovery systems are very diverse in different branches of industry including paper industry. A very important process applied in heat recovery units is condensate removal from the heat recovery units because of optimization of the heat recovery process and extending the working life of heat recovery units. Using of heat recovery units with condensate removal in paper industry fits the innovation trends and means heat energy saving that can be realized by increase of heat recovery efficiency. Heat recovery system with condensate removal should be installed near a drying cover of a paper machine due to reduction of heat loss and pipeline length. Integration of designed spiral heat recovery unit with condensate removal into the existing dryer section of paper machine in a paper mill will lead to decrease of heat consumption and increase heat recovery efficiency up to 91.7 %.

Waste agglomerated wood materials as a secondary raw material for chipboards and fibreboards. Part i. preparation and characterization of wood chips in terms of their reuse

The article describes a method of preparing particles from waste particle boards (chipboards) and oriented strand boards (OSBs). Their reuse is the main target of recycling. Method of their destruction was determined in this work. Agglomerated materials disintegrated after an initial destruction were further processed under specified conditions with regard to the material humidity, type of materials, contained adhesives and given characteristics of final particles – wood chips. Wood particles obtained were characterized by a fractional composition and amount of residual formaldehyde as an important parameter for the reuse of waste materials in production of furniture boards. New chipboards and pulp for production of middle density fiberboards (MDFs) will be provided from such defined particles.

Tackiness reducing of the stickies surfaces by inorganic agents and organic polymers

This paper present the results of application of inorganic minerals and organic polymers for elimination of sticky impurities “macrostickies” in the processing of recovered paper. The impact of individual agents has been monitored on different species of suspensions. On the dark suspension of recycled fibres VL5 with a brightness 53% ISO and an ash content of 17.6%, and the suspension VL1 with a brightness 64% ISO and an ash content of 29.4%. From inorganic minerals, the highest efficiency was achieved in the elimination of macrostickies using bentonite Hydrocol OT. At a dose of 5 kg bentonite.t-1 b.d. recycled fibres efficiency of 65.1% for suspension VL5 and 58.7% for VL1 was achieved. The highest performance of the Acefloc 2550 was achieved from the polymers. When applied to the VL5 suspension, the macrostickies were reduced by 57.1%, and when applied to the VL1 suspension, the macrostickies content dropped by 56.5%.

Waste agglomerated wood materials as a secondary raw material for chipboards and f ibreboards Part II. Preparation and characterisation of wood f ibres in terms of their reuse

The paper describes a process for the preparation of fibre from waste wood particleboards (PB), oriented strand chipboard (OSB) and medium density fibreboard (MDF). The purpose of recycling of agglomerated wood materials is to reuse them for the production of fibrous materials. The agglomerated materials disintegrated after the initial destruction were further processed under the specified conditions with respect to the moisture content, their type, adhesive used, and properties of final particles – wood chips. The obtained wood particles were characterized by the fractional composition of chips. The resulting chips were mechanically defibred with subsequent characterization of fiber obtained for its reuse in the manufacture of MDF. A quantity of formaldehyde released into the water when cooking waste MDF and PB was set up depending on the cooking time. Residual level of formaldehyde is the main chemical load that determines the amount of waste material that can be reused for production of new panels based on ureaformaldehyde adhesives.

Chemical processing of waste wood based agglomerates Part II: Evaluation of properties of fluting liners made of semichemical pulp obtained by an alkaline cooking process

The article describes the method of evaluation and preparation of fluting liners produced from semichemical pulp obtained from waste wood particle boards (PB) and oriented strand boards (OSB). The semichemical pulp was obtained using an alkaline cooking process from a sorted fraction of the 4-8 mm chips. Properties as thickness, bulk density, air resistance of paper sheet, tensile strength, tensile index, breaking length, burst index, CMT30 and SCT were monitored on lab sheets 127 g. m-2 and 170 g. m-2. Values of pH and residual NaOH were determined in the batch leachate.

A multi-stage cascade use of wood composite boards

A multi-stage cascade model was implemented on wood composite boards in four stages: particle boards → 100% recycling → middle density fibreboards → 100% recycling → paper liner. Preparation of composite boards bonded with urea-formaldehyde resin was simulated on plates 400 x 400 mm and final fiber was pulped using semi-production refiners to create the conditions closed to real. Mass changes and losses were observed during a whole simulated life process.
Results confirmed a deterioration of mechanical strength of recycled particle boards, the flexural strength in 13% and internal bond strength in 34% and slight increasing of the modulus of elasticity in static bending in 1.3%. Termomechanical pulping for the fineness in range 13°SR-24°SR (Schopper-Riegler) was chosen as appropriate for a fibrous board preparation from recycled chips, but their mechanical properties are at lowest levels compared to the requirements of standards. A low quality paper liner containing OCC, to improve its strength, was produced in the last stage of cascading.

Effect of steam explosion on enzymatic hydrolysis of various parts of poplar tree

The effect of steam explosion on enzymatic hydrolysis of various parts of poplar tree (heartwood, sapwood and 1-year coppice) was investigated. These parts were milled, the obtained sawdust was chemically analysed and then steam explosion of 0.7 mm poplar particles at temperature of 205°C was performed. Concentration of monomers obtained after enzymatic hydrolysis was considered as the main indicator for cellulose accessibility. Analysis of high performance liquid chromatography showed that non-treated poplar sawdust does not enable sufficient cellulose accessibility, while excessively high temperature and rapid pressure release resulted in substantial breakdown of polysaccharides and lignin and formation of inhibitors. The concentration of monomers increased gradually in the order of coppice, sapwood and heartwood. Steam exploded heartwood gave the maximum monosaccharides concentration of 90.0 g.L-1 after 72 hours of enzymatic hydrolysis. However, glucose concentration culminated after 48 hours of this hydrolysis. This corresponds to the best holocellulose accessibility for enzymes. The maximum concentration of inhibitors (9.3 g.L-1) was determined for poplar coppice after 24 hours of enzymatic hydrolysis.

Size reduction downcycling of waste wood. Review

The article includes research related to utilization of waste wood which is primarily size reduced due to its voluminity for next processing for lower value added products for about last twenty years. Procedures and results obtained by different authors were considered in one study. In this review a wood waste downcycling was consider as a process of transformation of large size wood products over their lifetime to the new products, where a size reduction is one of the first operations needed to achieve to. Incineration of each way was excluded from the present review, but second-generation biofuels are considered as potential products for the future. Two points of research selection according to origin and according to products made of waste wood was applied in this review. Comparison shown that the most industrially applicable implementation of treated particles obtained from waste wood is intended to the composite materials production as particleboards, fibreboards, cement-bonded and wood-plastics.

Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes Part II. Effect of steam explosion temperature on beech enzymatic hydrolysis

Beech wood is one of the most abundant species and the most harvested hardwood in Slovak Republic. The structure and chemical composition predetermines beech wood for the second generation bioethanol production. Steam explosion of beech wood from industrial treatment was investigated as a suitable pretreatment method. The effect of steam explosion temperature on beech sawdust enzymatic hydrolysis was investigated. Optimum steam explosion temperature at around 180°C was determined based on concentration of monosaccharides in hydrolysates and concentration of enzymatic hydrolysis inhibitors such as formic acid and acetic acid from beech sawdust. This corresponds to creating conditions resulting in good disintegration to the lignocellulosic structure which leads to increased cellulose accessibility. Non-treated beech sawdust does not enable sufficient cellulose accessibility while excessively high temperature results in significant breakdown of monosaccharides and lignin and formation of inhibitors. The concentration of inhibitors was also determined for each studied steam explosion temperature. Based on steam explosion of beech sawdust, the effect of severity factors was investigated to find the optimum conditions of steam explosion pretreatment on cellulose and xylan recovery of beech wood. The obtained optimum steam explosion temperature corresponds to severity factor R0 = 3.36 (180°C, 10 minutes).

Elimination of adhesive impurities of the recovered paper in flotation process

The article presents results of the elimination of sticky impurities from recovered paper in laboratory flotation of three pulp suspensions with different whiteness, obtained directly from the production line before entering flotation. A combination of commercial agents releasing undesirable substances from recovered paper and means for regulation and stabilization of froth and modified micronized bentonit was used. In the flotation purification of pulp suspension with a whiteness of 53%, the combination of Prodeink Extra, Prodeink AS10 and Hydrocol OT reduced the macrostickies content by 58%, the ash content decreased from 18.5% to 4.5%, the whiteness increased from 53% to 56.4% and the residual color content was reduced from 385 ppm to 294 ppm. The pulp suspension with a whiteness of 64% showed a reduction in the content of macrostickies by 66%, a reduction in the ash content by 23.2%, an increase in whiteness by 1.4% and a reduction in the residual color content from 245 ppm to 194 ppm. The pulp suspension with a whiteness of 68.3% showed a decrease in the content of macrostickies by 58.1%, the ash content decreased from 35.7% to 6.3%, the whiteness increased by 1.1% and the content of residual color decreased from 157 ppm to 117 ppm.