مجله صنایع چوب و کاغذ ایران
سال سیزدهم شماره 1 (بهار 1401)

In this study, the strengthening of cross-laminated timber (CLT) with glass fiber reinforced polymer (GFRP) on the lateral resistance (LR) of the single shear lap joints was investigated. Poplar (Populus alba) layers were used to construct the three-layer CLT. In first step, the effect of GFRP strengthening of CLT panel with three layers of FRP fastened with a lag screw, concrete screw, wood screw, and steel nail at an end distance of 1 cm on the lateral load capacity was investigated. In second step, the effect of the number of GFRP layers on the LR of the joint assembled with the lag screw with an end distance of 1 cm was investigated. Finally, the main effects of panel strength directions (major and minor axes), fastener types (lag screw, concrete screw, wood screw, and steel nail), and end distances (1and 2 cm) and their interaction on LR were investigated. The results showed that LR was increased by 22 to 53% with reinforcement, which was more considerable in joints with smaller diameter fasteners. By increasing the number of GFRP layers from one to three layers, LR was increased by 27%. By increasing the end distance, changing the fastener types and panel directions, LR was changed 114.7%, 219.6%, and 7%, respectively. The interaction of variables on LR showed that by simultaneously changing the fastener types × end distance, LR changed about 447%, which implied the importance of choosing the proper fastener with sufficient end distance to construct the joints with a metal connector such as brackets.

In this research, at the first stage of the study, the Pectin was reinforced with Polyvinyl Alcohol (PVA), and at the second stage, a combination of PVA reinforced Pectin and Nano Titanium dioxide (TiO2) was used to coat the packaging paper. After the coating process, the mechanical and optical properties of the samples were studied. Results showed that the second stage coating mixture enhanced the mechanical strength parameters of the papers (Tear from 16.55 to 17.85 KPa.m2/g, Tensile from 56.38 to 69.97 Nm/g and, Burst from 2.806 to 4.037 mNm2/g). In the brightness test, the paper samples coated with the first stage mixture showed a brightness decrease, while samples coated with the second stage mixture showed a brightness increase (the minimum brightness was 16.99% and the maximum brightness was 20.09%). On the other hand, the opacity of the papers coated with the second stage mixture was increased (from 97.88% to 98.67%).

There are various mechanical, chemical and thermal methods to improve the properties of wood which Their purpose is to block and reduce the reactivity of hydroxyl groups of cell wall polymers. The aim of this study is to modify the properties of Iranian beech wood ( Fagus orientalis L) via the passage of electricity.Three substances of water, salt solution in two levels and silver nanoparticles in two levels have been used to transfer electricity in wood. The experimental design was a factorial test on the basis of a completely randomized design to analyze the data obtained from the measurement of physical and mechanical properties. The results showed that the passage of electricity improved all the physical and mechanical properties of beech wood. Electric current passing via a 20% salt solution and 200ppm silver nanoparticles increased the Moduli of Rapture of beech wood respectively 25% and 29%. Electric current passing by both cause the Moduli of elasticity became more than fourfold And Anti-Swelling efficiency Based on the volume of beech wood obtained respectively 30% and 35%

In this study, the structural properties and thermal stability of cellulose nanocrystals produced from waste paper were investigated. Acid hydrolysis method was used to produce cellulose nanocrystals. Dimensions of nanoparticles were measured by FE-SEM microscope. To study the chemical structure and degree of crystallinity of nanoparticles, Fourier infrared spectrometry (FT-IR) and X-ray diffraction (XRD) were utilized, respectively. Thermogravimetric analysis (TGA) was performed to evaluate the thermal stability of nanoparticles. The diameter of nanoparticles obtained from virgin wood fibers, recycled fibers from MDF waste and waste paper were 18.94, 25.22 and 24.11 nm, respectively. The results showed a similar structure between nanocelluloses produced from different fibers, but a slight decrease in the thermal stability of nanocelluloses from waste paper was observed. Due to the similarity of the structure and properties of nanocellulose obtained from waste paper as compared to nanocelluloses obtained from other fibers, waste paper can be used as an available and valuable raw material for the production of cellulose nanocrystals.

In this study, the effect of radiofrequency plasma of hexamethyl disiloxane (HMDSO) on the physical properties and hydrophobicity of cellulose nanocrystals (CNC) was examined. Hence, crystallinity index, changes in functional groups, films surface topography, thermal stability (TGA) of pure CNC and plasma modified CNC (mCNC), dispersion in polar and non-polar solvents and static contact angle were investigated. The XRD spectroscopy showed no changes in CNC crystallinity index due to plasma treatment. Partial replacement of hydroxyl groups with Si groups was demonstrated by FTIR spectroscopy. Atomic force microscopy (AFM) images showed that the roughness of the mCNC film surface increased and thermogravimetric analyses (TGA) demonstrated more thermal stability of the mCNC compared to pure CNC. Hydrophobicity improvement of mCNC was also demonstrated by contact angle measurements. Also, the study of dispersion of mCNC in acetone showed that HMDSO plasma treatment is a suitable method to prepare better and more stable dispersion of mCNC in non-polar solvents.

In this study, the effect of using nanocellulose prepared from waste paper on the wear rate of friction materials used in car brake pads is investigated. An important part of the formulation of friction materials used in brake pads is reinforcing fibers, which in fact plays the role of the skeleton of the material. Different fibers are used in brake pads, such as iron fibers, rock fibers, glass fibers, etc. One of the most cost-effective fibers used in brake pads is cellulose fibers. Although cellulose fibers reduce the hardness of the pad and this is a grant, but they increase the wear rate. In this research, the possibility of using nanocellulos as alternative to cellulose fibers to improve the wear rate in the brake pad was investigated. The pads, which made by completely industrial method, were subjected to standard tests and their wear rate was measured in the wear and friction test concerning to the amount of mass reduction. The results show a 40% improvement in the wear rate of the brake pads using nanocellulose instead of commercial cellulose.Keywords: Nano cellulose, waste paper, brake pads, wear rate

The aim of the current study was to investigate the effect of using different charges of calcium hydroxide (as an alternative alkali source for sodium hydroxide) in hydrogen peroxide bleaching system of recycled pulp on paper strength properties and chemical oxygen demand (COD) of wastewater. The pulp mixture including recycled 70% newspaper and 30% magazine was deinked using a conventional (chemical) system and then bleached using a conventional hydrogen peroxide system under specified process conditions. The results indicated that the use of calcium hydroxide was relatively effective in enhancing the paper strength properties so that at the usage range of 2-4% calcium hydroxide, no significant reduction was observed in strength properties. On the other hand, with increasing the charge of calcium hydroxide to more than 4%, the strength properties of the paper increased relatively compared to the control sample (conventional peroxide bleaching system including sodium hydroxide alkali). Maximum values of tensile (35.64 Nm/g) and burst (2.98 kPa.m2g-1) indices were determined in experimental run C5 (10% calcium hydroxide) and maximum tear index (6.88 mN. m2g-1) was observed in experimental run C1 (2% calcium hydroxide). The amount of wastewater COD was much less than the control sample when sodium hydroxide was removed completely and replaced by calcium hydroxide in hydrogen peroxide bleaching, so that with increasing calcium hydroxide usage from 2% to 10%, the wastewater COD amount was still less than the control sample. Also, the results of the evaluation of the scale amount in the experimental run included 2% calcium hydroxide in comparison with the control sample indicated that the amount of scale in the bleaching wastewater was 145.24 mg/ml with 2% calcium hydroxide and in the control sample was obtained 32.87 mg/ml.

The layering process has been applied to modify the surface properties of solid materials including cellulosic fibers, in order to increase the amount of additives absorption on the surface of cellulosic fibers. Electrostatic attraction between charged particles and ionized surface of material is the major responsible for this process. Therefore, current research has been conducted to examine the effect of cationic starch degree of substitution (DS), and pH and conductivity of layering medium on zeta potential of recycled fibers. Accordingly, for 8 stage layering, pulp fibers suspension of old corrugated container (OCC) has been successively mixed with solutions of cationic/anionic starch. After each stage, the zeta potential of fibers has been measured. The obtained results showed an increase in zeta potential in fewer assembled layer when low DS of starch was applied. In layering in the pH range of approximately 7.5-10, larger amount of zeta potential has been measured. Additionally, the zeta potential has been increased in low conductivity conditions possibly, due to the more efficient configuration of starch particles around the fibers surface.

Surface treatment of paper and paperboard especially in size press has long history in the industry. Various starches and additives are used to improve the surface quality and surface sizing of the paper. But, application of starch and additives in size press is increasing with the purpose of improving the strength and packaging properties of recycled liner paperboard. Therefore, it is necessary to study the relationship between surface treatment process with additives and its impact rate on enhancement of certain resistance indices. So, in this research, starch with various concentrations (1-8%) and also following reinforcement with 5% nano-fibrillated lignocellulose were applied on the surface of industrially produced recycled liner board containing no additive. Also, viscosity variation was studied as one of the important variables. The results showed the surface treatment resulted in enhancement of all investigated strength properties. But the effect of increase in starch concentration and the amount of absorbed starch was not significant in some cases.

Paper recycling is one of the valuable conventional processes in the worlds. But in this process, some of recycled paper faces reduction in some of mechanical properties. Using different additives such as lignocellulosic nanofibers (LCNF) is one of the main solutions for improving these mechanical properties. In contrast with some other additives, the special physical and chemical structure of LCNF seems to be effective in its distribution in pulp suspension and also its performance. For this purpose, in this study, two mixing methods, conventional mixing (with mechanical stirrer) and intense mixing (with disintegrator) were considered. The results showed that increasing the mixing intensity of this mixture caused better dispersion of LCNF and the tensile index increased from 21 N.m/g in conventional mixing to 30 N.m/g in intensive mixing. In addition, considering the decreasing effect of LCNF application in pulp on its drainability, so after determination of proper mixing method, the effect of applying bentonite-chitosan microparticle system on its drainage was considered. The results indicated that this system could improve the drainage from 132 ml CSF in treatment containing only LCNF to 189 ml CSF in the treatment containing LCNF/ microparticle system with no effect on mechanical properties of final paper or even improving them.