Characteristics of Local Anisotropy Fields of Paper Structure and Deformation Properties

The results of a comparative assessment of the physical and mechanical characteristics of moisture-resistant packaging paper made of bleached softwood and hardwood pulp are presented. Non-destructive and destructive methods have been used to measure 60 g/m2 paper samples measuring 120×120 mm, divided into squares of 15×15 mm. The fields of characteristics in local areas have been obtained. In addition to the thickness lookthrough heterogeneity, the parameters of the local degree of anisotropy and the angle of orientation of the fibers have been determined using non-destructive total internal reflection IR-spectroscopy. Physical and mechanical properties have been determined during tensile testing of short-length samples. It has been revealed that floccules and gullies in a sheet of paper, visually expressed in the heterogeneity of the lookthrough, make a decisive contribution to the presence of local heterogeneity of anisotropy and the variation in the deformation and strength characteristics of the paper. The variation in the lookthrough heterogeneity measured in individual sections exceeds 11 % with a thickness variation of no more than 3 %. The coefficient of variation of deformation characteristics is several times greater than the coefficient of variation for the sample thickness and depends on the deformation area in which the parameters are measured. Analysis of experimental data and their statistical processing has made it possible to obtain a visual representation of the distribution of local characteristics of the structure, as well as deformation and strength properties. According to the distribution histograms and fields of local anisotropy of the structure and deformation properties of the paper, a very high variation in the structure parameters and the predominance of areas with reduced anisotropy compared to areas with high anisotropy have been established. A correspondence has been found between the fields of local strength characteristics: maximum strength, elongation to maximum load, and fracture work. It has been shown that the variation of mechanical characteristics increases with the transition from the elastic deformation zone and is maximum for parameters that integrally describe deformation and strength properties, such as fracture work.