Study On The Relationship Between Fiber Properties And Tearing Strength

The tearing strength is a very important factor of the physical properties of paper, the strength and morphology of fibers have a strong influence on the tearing strength and determine the tearing strength of paper.The effects of three principal fiber properties-length, coarseness and strength-on the tearing strength of paper have been studied. The effects of beating and pressing on the tearing strength of paper also have been investigated. The pulp materials of the experiment are masson pine, reed and straw. At first, sheets of approximately 120g/m2 basis weight prepared were divided into four batches. Sheets from three batches were guillotined into strips approximately 1mm, 2mm, 2.5mm wide respectively, another batch is uncut. The fiber length and coarseness of each pulp sample are determined by Kajaani FS-100 fiber length analyzer. Handsheets of 60 g/m are then made from each pulp over a range of bonding level obtained by varying the wet-pressing pressure during sheetmaking. A method, which allows changing the strength of the fibers in the sheet without affecting other fiber properties or sheet structure, is used to determine the effect of fiber strength on tearing strength. It consists exposing sheets for varying times to vapor of concentrated hydrochloric acid. We compared the coarseness of reed and straw to determine the effect of fiber coarseness on tearing strength. Finally a simply model is constructed.It was found that effect of the weight-average fiber length on the tearing strength was obvious. The correlation coefficient is 0.978 when we studied the effect of the weight-average fiber length on the tear index, but the correlation coefficient is 0.955 in the effect of the numerical-average fiber length on the tear index. At any degree of bonding, tearing strength is higher for the longer fibers. The degree of bonding required to reach a maximum in tearing strength is higher for the shorter fibers. The tear index is increasing with the wet-pressing pressure, the tear index is affected by the weight-average fiber length. The dependence of the weight-average fiber length is reduced at a high degree bonding for the longer fibers, however, even at a high degree of bonding, the tearing strength remains dependent on the fiber length for the shorted fibers. In a poorly bonded sheet of masson pine pulp, tearing strength depends on fiber length. The poorly bonded sheets which is made by straw, the correlated coefficient is 0.853 by investigating the fiber length to the tear index. However, it is only 0.816 in the well-bonded sheets. In a weakly bonded sheet, since more fibers pull out than break in the tearzone, the tearing strength is controlled more by the number of bonds the break along the length of the fibers. Thus tearing strength depends strongly on fiber length. On the other hand, in a well-bonded sheet, more fibers break than pull out in the tear zone, the effect of the fiber length is reduced. The tearing strength is increased with the increased fiber coarseness for the unbeaten pulp of reed and straw, but the tensile strength is decreased with the increased fiber coarseness. In a weakly-bonded sheet of the masson pine pulp, the tear index is approximately proportional to fiber length. In a well-bonded sheet of the masson pine pulp, the tear index is approximately proportional to (fiber length)1.5. For weakly-bonded sheets of masson pine pulp, the tearing strength depends on: T = K BdWRC-1L2.1; with increased bonding, the tearing strength depends on: T=K1 BdWRC-1L1.8+K2 B-2dWRC-1 f1. 5; for highly-bonded sheets, the tearing strength depends on: T~K fn , n>1.5.