The correlations among the tests values of bursting, tearing, tensile, tensile × elongation, drop number were studied.
The drop number was supposed as the function of the formula (I).
From the experimental data, the dependency of the drop number on the moisture content to the sack paper was given by the regression curve of the second degree (See Fig. 1).
It was concluded that the correlation between the drop number and bursting strength was not significant from the analysis of the data obtained in the drop tests of 600 sacks and the test values of bursting during past one year (See Fig. 2).
The correlation between the drop number and tearing strength was significant with 5% level of significance, so that the value of tearing test may be one of the measures which indicates the sack strength (See Fig. 3).
The drop number could be correlated to the value of the tensile strength x elongation and moisture content with 0.5% level significance (See Fig. 4).
It was quite clear from the stress-strain curves in the machine and cross directions and directional distribution of modulus of elasticity (See Fig. 5A &5B).
Therefore there was a significant correlationship between drop number and impact strength (See Fig. 6).
The bursting strength, which had not correlationship to drop number, is depend on the various factors, but the relation (5) …… (8) can be assumed as a first approximation. Approximate values of bursting stre.ngth can be computed by Fig. 5A, Fig. 8, Formula (8) and Fig. 9.
There was a significant correlation between bursting strength and ratio of the tensile strength in the machine and cross directions, if the paper are same basis weight and within definite region of tensile strength.