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GB/T 42697-2023 English PDF (GBT42697-2023)

GB/T 42697-2023 English PDF (GBT42697-2023)

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GB/T 42697-2023: Nonwovens -- Test method for porosity

This document describes a test method for testing the porosity of nonwoven fabrics by using the mass-density method and the true volume method. This document applies to all types of nonwovens except fluffy nonwovens.
GB/T 42697-2023
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 59.080.30
CCS W 04
Nonwovens - Test method for porosity
ISSUED ON: MAY 23, 2023
IMPLEMENTED ON: DECEMBER 1, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Principles ... 5
5 Instruments and equipment ... 5
6 Sampling ... 6
7 Humidity adjustment and test environment ... 7
8 Test steps ... 7
9 Result calculation ... 8
10 Test report ... 10
Nonwovens - Test method for porosity
1 Scope
This document describes a test method for testing the porosity of nonwoven fabrics by using the mass-density method and the true volume method.
This document applies to all types of nonwovens except fluffy nonwovens. 2 Normative references
The following documents contain the provisions which, through normative reference in this document, constitute the essential provisions of this document. For the dated referenced documents, only the versions with the indicated dates are applicable to this document; for the undated referenced documents, only the latest version (including all the amendments) is applicable to this document.
GB/T 6529 Textiles - Standard atmospheres for conditioning and testing
GB/T 24218.1 Textiles - Test methods for nonwovens - Part 1: Determination of mass per unit area
GB/T 24218.2-2009 Textiles - Test methods for nonwovens - Part 2: Determination of thickness
3 Terms and definitions
The following terms and definitions apply to this document.
3.1 true volume
The absolute volume after all internal void is removed.
3.2 apparent volume
The volume obtained by multiplying the thickness and area of the sample. 3.3 porosity
The percentage of nonwoven pore volume to apparent volume.
4 Principles
Method A (mass-density method): For single-component nonwoven fabrics with known fiber density, or multicomponent nonwoven fabrics with known density and content of each fiber, the true volume of the sample is calculated by the measured sample mass and the known fiber density; at the same time, the thickness of the sample is measured under a specified pressure and its apparent volume is calculated; then, the porosity of the sample is calculated by the true volume and apparent volume.
Method B (true volume method): For nonwoven fabrics with unknown fiber density or content, according to the ideal gas law (PV=nRT) of small molecule inert gases under certain conditions, the true volume of the sample can be determined by the measurement of the change in gas volume before and after the sample is placed in the sample chamber; then, the apparent volume is calculated by the thickness of the sample measured under the specified pressure, and finally the true density and porosity of the sample are obtained.
5 Instruments and equipment
5.1 Thickness tester
It shall comply with the requirements of 5.1 in GB/T 24218.2-2009.
5.2 True volume tester
The schematic diagram of the true volume tester is shown in Figure 1, which meets the following requirements:
a) High-purity compressed nitrogen source: It can provide stable high-purity nitrogen (purity reaches 99.999%), and the pressure can be adjusted according to test needs;
b) Sample chamber: It has good air tightness and the volume VC is 3??104 mm3~1.5??106 mm3, accurate to 100 mm3;
c) Air pressure sensor: It is connected to the sample chamber and has an accuracy of 0.01 psi1);
d) Additional chamber: Its volume VA is provided by the instrument manufacturer and accurate to 100 mm3; it can be connected to each other through solenoid valves, and be connected to the sample chamber through a solenoid valve; e) Solenoid valve: It has good air tightness; its opening/closing can be controlled 1) psi is a non-statutory unit of measurement, 1 psi???6.89 kPa.
The sample shall be cut at least 100 mm away from the edge of the cloth; smooth the cloth gently and then take the sample at a uniform area; avoid deforming the sample due to forceful stretching.
7 Conditioning and testing environment
The standard atmosphere for conditioning and testing shall be in accordance with the provisions of GB/T 6529.
8 Test steps
8.1 Thickness test
For conventional nonwoven fabrics, carry out the test according to Method A in GB/T 24218.2-2009. The test pressure is 0.1 kPa. Use a thickness tester to measure the thickness t, accurate to 0.01 mm.
After negotiation between the relevant parties, the thickness can be measured directly with a ruler or measured through other pressure, and the specific methods and parameters shall be noted in the report.
8.2 Method A (mass-density method)
Determine the mass w per unit area of the sample according to GB/T 24218.1. According to the fiber density and content of each component in the sample, calculate the porosity of the sample according to 9.1.
8.3 Method B (true volume method)
8.3.1 Measure the transverse length and longitudinal length of each sample separately, accurate to 1 mm.
8.3.2 Roll the sample into a roll and put it into the sample chamber, close the sample chamber, and open the solenoid valve 2# and the solenoid valve 3# shown in Figure 1; open the nitrogen source and the solenoid valve 1# to allow nitrogen to enter and clean the sample chamber and the additional chamber, and the cleaning time is at least 2 minutes.
8.3.3 Close the solenoid valve 1# and set the air pressure in the sample chamber and additional chamber to zero point.
8.3.4 Close the solenoid valve #2 and the pressure relief valve, and open the solenoid valve #1 to allow high-pressure nitrogen to enter the sample chamber and stabilize the air pressure in the sample chamber to 10 psi (P2).

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