GB/T 24328.3-2020Tissue paper and tissue products - Part 3: Determination of tensile strength, stretch at maximum force and tensile energy absorption (English PDF)

5.1 Tensile-testing apparatus

5.1.1 General

The tensile-testing apparatus shall be in accordance with GB/T 12914. It is capable of stretching a test piece of tissue paper or tissue product of given dimensions, at a constant rate of elongation of (50 ± 2) mm/min, and recording the tensile force as a function of elongation on a strip chart recorder or any electronic device.

The elongation shall be recorded to an accuracy of ±0.1 mm. The measurement of the elongation shall start at a tension of (1.0 ± 0.5) N/m.

The force-measuring system shall measure loads with an accuracy of ±1 % of the reading or ±0.05 N, whichever is greater, and shall be calibrated and verified regularly.

5.1.2 Means for measuring the area of the force-elongation curve

The tensile-testing apparatus shall provide a means for measuring the area between the force-elongation curve and the elongation axis to an accuracy of ±2 % of the true value as determined by numerical integration of the raw data.

Note: Most modern tensile testers are equipped with an electronic or electro-mechanical integrator. The area can also be determined from a graphical output of the data on chart paper using a planimeter.

5.1.3 Clamps

The tensile-testing apparatus shall have two clamps of 15 mm or 50 mm in width. Each clamp shall be designed to grip the test piece firmly along a straight line across the full width of the test piece, without causing any damage or slippage, and shall have means for adjusting the clamping force.

The clamps should preferably grip the test piece between a cylindrical and a flat surface, with the plane of the test piece tangential to the cylindrical surface. be free of creases, kinks, wrinkles, folds or other thickness variations.

For finished products with dimensions or perforations which make cutting of a test piece of 150 mm impossible, cut the longest piece possible. In such cases, a test span length of (50 ± 1) mm shall be used. This deviation from the normal procedure shall be recorded in the test report.

7.3 Number of test pieces

Cut 10 test pieces from one sample and 10 test pieces in the cross direction for the selected specimens, making a total of at least 20 test pieces from each sample.

9.1 General

Calculate and report the results separately for the machine direction and for the cross direction from Formula (1) to Formula (6).

Where: A - the mean stretch at maximum force in %;

epsilon - the mean elongation at maximum force in millimetres (mm); l - the length of the test piece between the clamps, before elongation, in millimetres (mm). Report the result to the first decimal place.

9.5 Tensile energy absorption

Determine the area under the force-elongation curve up to the point of maximum tensile force and calculate the tensile energy absorption from Formula (4): and the mean tensile energy absorption,, from Formula (5):

Where:

Z - the tensile energy absorption by a test piece during the test until maximum force, in joules per square metre (J/m2);

- the mean tensile energy absorption in joules per square metre (J/m2);

E - the work, in millijoules (mJ), equivalent to the area under the force/elongation curve; w - the initial width, in millimetres (mm), of the test piece (standard width is 15 mm or 50 mm); l - the initial test length, in millimetres (mm), of the test piece (standard 100 mm); n - the number of single values of the tensile energy absorption.

Report the mean tensile energy absorption to the first decimal place.

9.6 Tensile energy absorption index

Calculate the tensile energy absorption index, lZ, using Formula (6): […]

A.1 General

A.1.1 The qualified laboratories of the Comparative Testing Service of the Confederation of European Paper Industries (CEPI-CTS) conducted a comparative test on 2 tissue paper products. The data for tensile strength are presented in A.2. The data for stretch at maximum force are presented in A.3.

A.1.2 The repeatability and reproducibility results from the test are reported in Table A.1 to Table A.4.

A.1.3 Precision data for tensile energy absorption is not available at the moment.

A.1.4 The calculations were made according to ISO/TR 24498 and TAPPI T 1200 sp-07.

A.1.5 The repeatability standard deviation reported in Table A.1 and Table A.3 is the "pooled" standard deviation, which means that the standard deviation is calculated as the root-mean-square of the standard deviations of the participating laboratories. This differs from the definition of repeatability in ISO 5725-1.

A.1.6 The repeatability and the reproducibility limits are estimates of the maximum difference of the data, which is obtained from the tests of two similar materials in the similar test environment, under a 95 % confidence interval.

These estimates may not be valid for different materials or different test conditions. Repeatability and reproducibility limits are calculated by multiplying the repeatability and reproducibility standard deviations by 2.77. The repeatability standard deviation and the within-laboratory standard deviation are identical. However, the reproducibility standard deviation is not the same as between-laboratories standard deviation. The reproducibility standard deviation includes both the between-laboratories standard deviation and the standard deviation within a laboratory, viz.: s = shn s = shn + sn

Note: 2.77 = 1.96 sqrt2, provided that the test results have a normal distribution and that the standard deviation, s, is based on a large number of tests. […]