Impact Penetration Testing for Textiles Part 1
Impact Permeation tests assess the resistance of fabrics to the permeation of water by impact. The test was designed to predict the probable rain permeation resistance of a fabric and most procedures still include this language in the scope. The test has also been followed by the medical industry as an assessment of liquid barrier performance for protective apparel and drapes.
A test sample is mounted firmly, face-up on an angled surface. A pre-weighed sheet of blotter paper is mounted behind the sample. An amount of water is sprayed against the face of the sample. The blotter paper is then re-weighed to discover water permeation . The raise in mass of the blotter paper shows the mass of water that passed through the test sample. Lower test results show less permeation and superior water repellency of the fabric.
There are several varieties of this test, all based on the AATCC test procedure actually issued in 1945. Perhaps most eminently for the present environment, the impact permeation test is one of several used to assess Level 1-3 barrier materials for medical personal protective appliance. Anyone evolving, producing, or checking surgical gowns, isolation gowns, other protective apparel, surgical drapes, or drape accessories must understand how to select the correct test procedure.
ANSI/AAMI PB70, Liquid barrier performance and categorization of protective apparel and drapes designed for use in health care facilities, figures the requirements for protective apparel and drapes.
AATCC TM42, Test Procedure for Water Resistance: Impact Permeation is a required test for materials categorized as Level 1-3; however, it must be executed with a substitute blotter paper. The blotter paper specifications are incorporated in the AAMI PB70 standard.
The latest version of AAMI PB70 also permits WSP (Worldwide Strategic Partners) 80.3 as an alternate for AATCC TM42. WSP 80.3 has since been replaced by NWSP (Nonwovens Standard Procedure) 80.3. The blotter paper stated in these procedure is close but not exactly the same as that described in AAMI PB70. Different versions of NWSP 80.3 define different mass per unit area, while the AAMI standard registers no value for this property. Since no year is mentioned, one can presume that the most recent version of NWSP 80.3 should be used.
Although the AAMI standard shows that the procedures are equivalent, there are small dissimilarities that could influence results for some materials. All reports should show which impact permeation test was executed. A total comparison of the AATCC and NWSP procedures is incorporated below.
The blotter has been a source of puzzlement and vexation. The blotter paper conventionally used for AATCC TM42 should NOT be used for testing and categorization of barrier performance according to AAMI PB70. As mentioned above, the blotter paper described in the AAMI and NWSP standards are not quiet the similar. A complete clarification of the differences is included below.
For practical purposes, EDANA (the publisher of NWSP 80.3) prescribes Ahlstrom grade 989 blotter paper, while showing that other papers may also be appropriate. Note that not all properties stated in AAMI PB70 or NWSP 80.3 are listed on data sheets given by the blotter paper manufacturer and not all properties listed meet the specifications exactly. For instance, one data sheet shows a objective absorbent capacity of 512.0%, with a minimum of 434.0% and a maximum of 590.0%; AAMI PB70 requires an absorbent capacity of 480% ±30% (450% – 510%); NWSP 80.3 requires an absorbent capacity of ≥ 480%.
For AAMI PB70 Level 1-3, execute AATCC TM42-2017e as written, with the exception of the blotter paper. Use blotter paper meeting the specifications listed in AAMI PB70, section 220.127.116.11. For borderline results on nonwoven fabrics, it may be advantageous to use a Type II tester to lower the vibrations during testing.
As a substitute, perform NWSP 80.3.R1 (19) as written. Use blotter paper matching the specifications listed in NWSP 80.3.R1. Be assured to show the version of the procedure used as there are notable differences in the blotter paper specified in earlier versions.
Carry out AATCC TM42 or NWSP 80.3 to meet AAMI PB70 requirements; do not execute both tests.
Use the sampling plan showed in AAMI PB70 whether testing with AATCC TM42 or NWSP 80.3. This will normally require more samples than called for in the test procedures. In most cases, 15-20 samples per element is suitable. If fewer samples are examined on account of limited sample size or agreement among all parties, this should be mentioned in the test report.
While AATCC TM42 and NWSP 80.3 are designed for testing unstitched fabric, AAMI PB70 also needs testing of seams and attachment points as these are the most probable point of failure for water resistance. Test each applicable element of the protective apparel or drape independently.
Center seams widthwise so they run along the length of the sample. Center points of attachments on the sample (see Fig. 1). Check multi-layer products as they are used in the final product—incorporate all layers in the right order, outermost layer on top. Specific instructions on crucial zones for testing is added in AAMI PB70.
Execute further tests (AATCC TM127, ASTM F1671, ASTM F1670) as required, depending on intended AAMI PB70 categorization level.
* For AAMI PB70 Level 1-3, perform AATCC TM42-2017e as written, with the exception of the blotter paper. Use blotter paper matching the specifications listed in AAMI PB70, section 18.104.22.168.
* As a substitute, execute NWSP 80.3.R1 (19) as written. Use blotter paper matching the specifications listed in NWSP 80.3.R1.
* In most cases, 15-20 samples per element is appropriate.
* Test each applicable element(base material, seam, attachment, etc.) of the protective apparel or drape independently.
* Execute further tests (AATCC TM127, ASTM F1671, ASTM F1670) as required, depending on intended AAMI PB70 categorization level.