MODIFIED STARCHES AS A MEAN OF INCREASING THE DRY STRENGTH OF TISSUE PAPERS

Application of agents to increase the dry strength is one of the ways of improving the physical-mechanical properties of papers. In the presented article, we are dealing with the application of modified starches to the pulp mass in order to increase the strength parameters of hygienic papers. In laboratory experiments, 8 types of agents were tested, which differed in charge level, molecular weight and cross-linker level. Strength parameters, porosity and water absorption were evaluated during the laboratory tests. The most important strength parameter in the production of tissue papers is the tensile strength, the most suitable parameters for the production of tissue papers were achieved when applying the product ECO 2777. By monitoring the influence of the dose of starch, it was found that the optimal dose is 3 kg per ton of absolutely dry pulp, when there is an increase in the tensile strength by 18%, the burst strength by 41% and while maintaining the required values of stiffness, porosity and water absorption

Effect of Water Absorption on the Mechanical Properties of Silane-Treated Wood Flour Polypropylene Composites

The behavior of the wood flour-polypropylene composites prepared with various contents of untreated and silane-treated wood flour by immersion in water was studied, as well as the effect of the water absorbed by the samples on their mechanical properties. The highest degree of water absorption was observed for the composites containing 30 – 50 mass% alkali pre-treated wood flour. For the materials with 50 mass% untreated, silane-treated and alkali pre-treated wood flour, the water absorption measured was 8.76%, 7.84% and 13.91%, respectively, after 15 days immersion in water. The value of the thickness swelling calculated for the samples prepared with 50 mass% silane-treated wood flour – polypropylene was the lowest – 1.29%. It was proved that the absorption of water molecules results in change of the tensile profile of the thermoplastic polypropylene composites filled with hygroscopic filler.

Effect of wood flour content on the properties of flat pressed wood plastic composites

This study focused on the effect of wood flour content on some mechanical and physical properties of flat pressed wood plastic composites (WPC). The results revealed changes in the wood flour content affected the density of flat pressed WPC. Moreover, as exposure time increased, water absorption values were increased. The changes in the wood flour content considerably affected the mechanical properties of WPC. The decrease in the flexural strength reached up to 58%, while it was 61% for tensile strength. However, modulus of elasticity increased with increasing wood flour content. Meanwhile, the decrease was inevitable for screw withdrawal strength, where the increase in wood flour content resulted in a reduction of up to 50%. It was clearly determined that wood flour content above 60% evidently affects the physical and mechanical properties of flat pressed WPC, which should be considered in the utilization areas where high mechanical properties are critical.

The effects of expoxidized soybean oil on the mechanical, water absorption thermal stability and melting processing properties of wood plastic composites

To promote the environmentally friendly properties of wood plastic composites (WPC) fabricated via a polyvinyl chloride resin matrix, the effects of different amounts (0, 5, 15, 25, and 35 phr) of expoxidized soybean oil (ESO) on mechanical strengths, thermal stability, melting processing properties, and water absorption of the composite samples were studied. The results show that the tensile strength of WPC decreased. However, the elongation at break, water absorption and thickness swelling rates increased, especially for ESO addition amounts beyond 15 phr. The flexural strength and modulus of WPC followed an upward trend initially (at 5 phr ESO), then switching to a downward trend. The initial thermal stability at the first thermal decomposition stage and the melting processing temperature of the composites ewere effectively improved with the increase of ESO level. Compared to the samples without added ESO, the maximum thermal decomposition temperature (Tmax1 and Tmax2) values of the composites increased by 31°C and 8°C, respectively, while the melting processing temperature of the composites significantly decreased by 24°C corresponding to an added level of 35 phr. In summary, the WPC samples with 5-15 phr ESO addition not only effectively retained their the mechanical strengths and water absorption stability, but also improved their the thermal stability and melting processing properties.

Comparison of capillary flow porometry and mercury intrusion porosimetry in determination pore size distribution of papers

Capillary flow porometry and mercury intrusion porosimetry achieved a good agreement in determining the pore size distribution in papers for the top layers of corrugated board. Differences in the papers composition as well as structure can be easily detected by changes in the measured parameters, thus allowing a better understanding their behaviour at processing and use. Water absorption is mainly dependent on the diameter of the large pore and to a lesser extent from the diameter of medium pore, surface free energy of paper and the swelling ability of recycled and bleached pulp fibres.

Oxidative and reductive bleaching of deinked pulp

Deinked pulps for hygienic paper production were bleached with hydrogen peroxide and sodium dithionite in single and two-stage bleaching. The brightness gain of high brightness deinked pulp in the peroxide stage was 5.7% ISO and of low brightness 4.4% ISO. In sodium dithionite stage, the brightness gain of high brightness deinked pulp was 4.0% ISO and of low brightness deinked pulp 3.8% ISO. The two-stage oxidative-reductive bleaching sequence resulted in an increase of brightness by 9.7% ISO for high brightness deinked pulp and by 9.1% ISO for low brightness deinked pulp. Brightness gain in the two-stage reductive-oxidative bleaching sequence was 6.7% ISO for high brightness deinked pulp and 5.6% ISO for low brightness deinked pulp. The coordinate b* value and yellowness of deinked pulps decreased in sodium dithionite bleaching stage more than in hydrogen peroxide stage. The two-stage oxidative-reductive bleaching sequence is more preferred than reductive-oxidative sequence regardless of the fibre composition. The tensile index and the tensile energy absorption index of deinked pulps slightly decreased after single-stage and two-stage bleaching sequences, their reduction in the peroxide stage was greater than in the dithionite stage. The fibre strength and fibre length characteristics of deinked pulps decreased after bleaching, while fibre bonding ability increased. The water absorption and bulk softness increased after bleaching, the increase was higher after peroxide stage than dithionite stage.

Blending impact of hardwood pulps with softwood pulp on tissue paper properties

The influence of proportions of bleached birch, eucalyptus, beech kraft pulps as well as the bleached aspen chemi-thermomechanical pulp (BCTMP) in the mixture with bleached pine kraft pulp on tissue paper properties was compared. Increase of bleached beech kraft pulp and aspen BCTMP proportion in a mixture with bleached pine kraft pulp leads to significant rise of porosity ε as well as bulk. The water absorption after immersion increased significantly with increase of aspen BCTMP content in the mixture while other hardwood pulps in the mixture had only moderate impact. Increasing of bleached beech and eucalyptus kraft pulps content in the mixture continually increased initial water absorption. As a result of blending of bleached birch kraft pulp with bleached pine kraft pulp, bulk softness improved and the tensile index increased slightly. The increased content of bleached birch and beech kraft pulp in the mixture increased the brightness while the addition of aspen BCTMP and bleached eucalyptus kraft pulp increased of coordinate b* value. Mixed pulps with properties suitable for different types of hygienic products were selected.

Relationship between structural parameters and water absorption of bleached softwood and hardwood kraft pulps

The influence of porosity, relative bonded area and air permeability on water absorption of unbeaten and beaten bleached kraft pulps from different wood species used for tissue paper production was investigated. The water absorption was determined by four different methods such as absorption of water after immersion, initial water absorption, water absorption capacity and saturation rate with water. Linear dependences between water absorption parameters and the structural parameters of individual pulps as well as all tested pulps were obtained. The correlation coefficients obtained within individual bleached kraft pulps were from 0.95 to 1.00 and within the whole group of pulps were from 0.86 to 0.98. Relative bonded area and air permeability were found to be the most suitable parameters for predicting of initial water absorption and saturation rate with water.

Effect of addition of deinked pulp to bleached kraft pulp on tissue paper properties

The influence of addition of deinked pulps with low and high brightness to bleached eucalyptus and pine kraft pulps on functional tissue paper properties was studied. Deinked pulps with low and high brightness had some different functional properties. Deinked pulp with high brightness has higher bulk, porosity, water absorption after immersion, initial water absorption, bulk softness as well as brightness. On the contrary, the difference in relative bonded area and porosity e between deinked pulps with low and high brightness was moderate. The mixed pulps laboratory pulp sheets from bleached eucalyptus kraft pulp or bleached pine kraft pulp with addition of 20, 40 and 80% of deinked pulp with low brightness or deinked pulp with high brightness were prepared. The addition of the deinked pulp with high or low brightness to bleached kraft pulp leads to increasing of bulk, bulk softness as well as high water absorption after immersion and initial water absorption. The tensile index rapidly decreased by the addition of deinked pulps with high brightness to bleached eucalyptus and pine kraft pulps. Similarly, the addition of deinked pulp with low brightness to bleached pine kraft pulp led to rapid decreasing of tensile index. On contrary, with the addition of deinked pulp with low brightness to eucalyptus kraft pulp, the decreasing of tensile index was less pronounced. Mixed pulp from bleached eucalyptus kraft pulp with a small content of deinked pulp with low brightness with functional properties suitable for production of tissue papers was found as optimal.