Research On Wet-web Strength Of Paper Sheet With The Addition Of Cellulose Nano-fibrillated(CNF)

There is a clear trend in the paper industry towards lower grammages and higher machine speeds to increase productivity while conserving resources and energy.Especially in packaging paper grades,there is a trend to decrease basis weight from 110 to 130 g/m2 down to 70 to 90 g/m2 with machine speed up to 1900 m/min.The strength of paper web determines the successful transfer of paper sheet among the rolls.Particularly,tensile strength of the wet web in the press-to-dryer-section transfer area is only 10?15%of the strength of a dry web,which effect the frequency of wet-web breaks.Thus,the strength of wet web is a key parameter in papermaking process.In this thesis,the effects of cellulose nano-fibrillated(CNF)and cationic cellulose nano-fibrillated(CCNF)on the wet-web strength and the effect of the distribution of CNF were studied with soft bleached kraft pulp.Firstly,the effect of CNF addition on the wet-web strength and pressability of paper sheet during the press process of papermaking was explored.It was found that the tensile energy absorption(TEA)of the sample was increased from 6.32 to 10.93 J/m2 at 50%wet web solid content when 5%CNF was added.The web solid content was decreased from 50.5%to 42.9%when 0%?5%CNF was added under the same drainage and pressing conditions,indicating that the addition of CNF during the paper-making process can retard the pressability of paper sheet.The roles of CCNF as versatile flocculants of wood pulp and fines in pulp slurry for high wet web performance found that the density of paper sheet reached to the highest at 0.26 g/m3,which was 0.05 g/m3 higher than that of the original paper without CCNF addition.The fines retention was increased from 86.9%to 91.3%when the CCNF-3 addition increased to 5%,which was 1.05 times higher than that without CCNF-3 addition.Thus,CCNF can induce significantly flocculation(CCNF-Fines complex)in pulp slurries.The mechanical properties of wet web can also be improved by the addition of CCNF.The study demonstrated that CCNF can act as effective flocculants of fines and form CCNF-Fines complex for improved wet-web strength.CCNF is more beneficial to the wet web performance when it is in higher charge density.To study the influence of different distribution of CNF on the strength performance of paper sheet,and the results showed that CNF(mixture)has the most positive impact on tensile strength of paper sheet.Comparing the XPS experimental data of CNF paper sheet with different distribution showed that the peak of C-O varied drastically,and CNF(mixture)had the highest peak,then CNF(middle),CNF(surface)and when paper sheet without CNF was the lowest one.Therefore,CNF improved the strength of paper sheet mainly by increasing the amount of hydrogen bonds in the paper sheet and CNF(mixture)exists the largest bonded area between fibers and CNF,which keep fiber and CNF bonded together tightly with hydrogen bonds.