Fiber length, coarseness and strength is the three basic properties of paper fibers, and paper performance has a close relationship with the physical properties of paper and printing performance, the absorption and porosity of the paper sheet has a greater impact.

Here we are going to discuss the effects of fiber properties on paper properties by six points:

• The effect of fiber length and coarseness on paper uniformity
• The effect of fiber length and thickness on paper breakage resistance
• The effect of fiber length and coarseness on paper tightness
• The effect of fiber properties on tensile strength
• The effect of fiber properties on paper tearing
• The effect of fiber length and strength on paper folding strength

The effect of fiber length and coarseness on paper uniformity

Seth has done a series of studies with unpunched chemical pulp, and for unbleached sulfate pulp, as the fiber length decreases, the more uniform the sheet is. This leads to the conclusion that the shorter the fiber, the better the formation. For the coarseness of the fiber, there is a similar conclusion, that is, the finer the fiber, the better the evenness, the more favorable to the formation. Long fiber sheet forming is poor, mainly due to the flocculation of long fibers in the sheeting process, while short fibers are easy to flow, good water filtration, the formation of a more uniform sheet.

The effect of fiber length and thickness on paper breakage resistance

Breakage can be calculated by tensile index, breaking strain, fiber length and fiber roughness. Among them, the length of the fiber on the paper breaking degree of great effect, the longer the fiber, the better the combination, the greater the breaking degree. Studies have shown that the greater the fiber thickness, the greater the thickness of the loosening, the lower the breaking strength.

Since breaking strength is a comprehensive parameter effectd by tensile strength and elongation, and all these strength indicators are effectd by fiber length. The reason for increasing the fiber length to improve the breaking strength is the increase of the mutual contact between the fibers.

The effect of fiber length and coarseness on paper tightness

When fiber length and coarseness are both low, the fibers tend to form a more compact network system. As the fiber length decreases, the tightness of the resulting paper sheet increases. A similar conclusion was reached for fiber coarseness. That is, the tightness of the paper with the increase in fiber thickness and decline, the main factors affecting fiber coarseness, fine fibrillation, wrinkling during drying and pulp content of fine fibers. The impact of fiber coarseness on paper tightness may be caused by the impact of fiber coarseness on the wet flexibility of the fiber, because

The greater the coarseness of the fibers of its mixed flexibility is relatively small, and therefore in the paper forming, the interweaving area between the fibers and the bonding force is relatively small, so that the tightness of the paper is also smaller.

The effect of fiber properties on tensile strength

Tensile strength increases with increasing fiber length, as longer fibers provide more bonding points, while longer fibers themselves have higher strength. It is conducive to uniform stress distribution. At a certain sheet tightness, tensile strength increases with the increase in fiber length, but when the length exceeds a certain value, tensile strength does not further increase, this is because when the fiber reaches a certain length, there are a considerable number of bond points, pulling out the fiber than pulling off the fiber is difficult, then the tensile strength is mainly controlled by the fiber strength, no longer with the increase in fiber length and change.

In different pulping revolutions, by different fiber thickness of the pulp copied paper, its tensile strength with the increase in fiber thickness gradually reduced, because the tensile strength of paper depends mainly on Ding inter-fiber bonding force. With the increase in fiber coarseness, the specific surface area decreases, the tensile strength decreases. By the fiber coarseness of the pulp copied from the paper, the interfiber bonding force is relatively small, and therefore, the tensile strength of the paper is relatively small.

Tensile strength is also affected by fiber strength and fiber combination of two aspects, when the fiber combination is weak, the combination of fiber index as the main determinant, and thus the tensile strength is mainly controlled by the fiber combination; if the fiber combination degree, the combination of the index of the impact is smaller, at this time, the impact of fiber strength is more important.

The effect of fiber properties on paper tearing

Fiber strength, coarseness and sheet tightness remains constant, fracture toughness with the average length of the fiber increases, approximately a linear relationship.

For paper tearing, the main influencing factors for the paper's ability to resist local stress and the ability to disperse local stress size, the greater the fiber thickness of the pulp, the smaller the inter-fiber bond, which on the one hand, causing the paper to disperse the local stress capacity to increase. But on the other hand, the paper resistance to local stress ability to reduce, as to which side is dominant, it is not known, there is still a need for further research. The greater the fiber thickness of the pulp fiber length is relatively larger, and fiber length on the impact of the tearing degree, the greater the visible fiber length, the greater the relative tearing degree of the paper. Due to the combined effect of the above three factors. The tearing degree of the pulp increases with the increase in fiber thickness.

The strength of the fiber on the paper folding degree of effect and the degree of bonding between the fibers is closely related. Some studies have shown that when the fiber is long, there is sufficient combination, the tearing degree and the square of the fiber strength is proportional, if the fiber is shorter, combined with poor, the dependence of the tearing degree on the fiber strength is weakened, because at this time in the tearing part, the fiber is usually pulled out, rather than pulling off.

The effect of fiber length and strength on paper folding resistance

Folding resistance to fiber length has a very high dependence, folding resistance with the increase in fiber length and paper tightness and improve, and the longer the fiber, the better the combination, the more increase. Fiber strength has a great effect on the folding resistance, some research results show that the folding resistance and fiber strength of 6 ~ 8 times proportional to a minimum.

Conclusion

Fiber length, coarseness and strength as the basic properties of the fiber, the formation of the paper sheet has a direct impact. The impact of the three on the formation of paper, both interrelated and mutually influencing, complementary, in the actual production, comprehensive consideration of their impact is necessary.

Fiber length on the paper properties of a wide range of impact, almost all strength properties as well as forming, but the degree of impact is very different. Fiber length for a certain type of paper to have a minimum length pole, less than this limit, to affect the quality of paper, so require fiber length to be greater than this minimum length limit, in order to help improve and improve the quality of paper. Reduced fiber length, in addition to improving the formation of the structural properties of the paper sheet does not have much direct impact, but lead to a decline in mechanical strength, especially on the folding and tearing degree of greater impact, relatively speaking, the impact on the tensile strength is small, because the tensile strength is mainly affected by the combination of fibers. Generally speaking, longer fibers give higher strength to the paper sheet, especially for poorly bonded sheets. When the paper is well bonded, the effect of fiber length becomes less important.

The impact of fiber thickness is ultimately due to the impact of fiber bonding. Thicker fibers have thicker cell walls, fewer fibers per unit mass, and a smaller specific surface area, resulting in a paper sheet that is thick, porous, and rough. Poor uniformity, opacity is small, the tensile strength of the paper is poor, but the tear strength is greater, and therefore suitable for the production of paper requiring thickness and porosity; and coarser fibers are suitable for the production of strength, stiffness, smoothness and opacity of high paper.

Fiber strength of the impact on the strength of the paper page is also closely related to the degree of fiber bonding, the combination of poor paper, its impact is very small, because the paper sheet fracture occurs mainly in the combination of parts, rather than fiber fracture; and the combination of good paper, fiber strength greatly affects the strength of those controlled by fiber fracture nature, the reduction of fiber strength will lead to tensile strength, breakage and folding resistance decreased significantly, especially Fold resistance decreases more seriously. As the vast majority of paper sheets are well bonded, fiber strength directly affects the strength of the paper, so in the process, the loss of fiber strength should be reduced to a minimum.

(Network-秦丽娟, 陈夫山, 王高升. 纤维的性质对纸张性能的影响[J]. 生活用纸, 2004)