Testing for Coated TextilesSubmmited to: Dr Munir Ashraf Submitted by: Muhammad Jehanzeb Tariq (11-145)Section: C (Textile chemistry) 8th semester

Introduction

Testing for coated textiles depend upon the type of coating material, the end use of the article etc. There are a number of tests for coated textiles including those which are also used for conventional textiles like breaking strength, tear strength etc. The test standards used are mainly ASTM and BS. The major testing for coated textiles are Coating adhesion, resistance to water permeability and assessing wearing and ageing etc. A few tests are being discussed below which are purely for coated textiles:

Tests for Durabiity:

1. Degree of Fusion (BS 3424, ASTM D 4005-81)

Coatings like PVC are applied in dispersion form which on curing, fuse to form a continuous film. In order to evaluate the durability of coaing degree of fusion is very important. It is evaluated by imersing a test specimen of 40 × 25 mm2 in acetone for 15 min at 20 ˚C (BS) or for 30 min at 23 ˚C (ASTM) and then coating is examined, if there is no cracking sample is said to be good fusion. For rubberised material xylol is used instead of acetone for 2 hours at 27 ˚C. The sample is to be cured good if there is no tackiness or detachment from base fabric.

2. Coating Adhesion (BS 3424, ASTM D-751)

This test is performed within two mechanisms i.e. either by dynamic method or dead weight method. According to BS tset specimens of 75 × 200 mm with length along the width of the fabric are cut, if coating is thick it is manually stripped to 50 mm and specimen width is trimmed to 50 mm. In dynamic method, the separated plies of fabric are clamped in autographic strength testing machine with constant rate of traverse. Coating is separated for 100 mm by setting traverse jaw in motion. The adhesion strength is calculated by load required to separate coating layer.

The dead weight test apparatus consists of a top fixed grip and a bottom free grip, capable of accepting dead loads of 200 g units. The test specimens are attached to the grips and weight is loaded on the jaw of lower grip until coating separates. This load is recorded. In case of thin coating two specimens are bonded face to face by an adhesive system leaving 50 mm free. At the adhesion line layer of fabric and two layers of coating are undressed manually. The adhesion strength is determined by the same dynamic mechanism as described above.

3. Accelerated Ageing (BS 3424, ISO 7016)

Accelerated ageing test is carried by two methods: Oven method and Oxygen pressure method. In oven method specimen undergoes heating at 70 ˚C or 100 ˚C for 168 hours and is observed for ageing effects like softening, stiffening and sticking. In oxygen

method test specimen is hanged in a stainless steel pressure chamber at elevated conditions of 2000 kN/m2 and 70 ˚C for 24 hours. For vinyl coated fabrics estimation of plasticizer is important and is evaluated by ASTM D- 1203 which includes the use of activated carbon under defined conditions. For elastomer coated fabrics ozone cracking test is carried out by ASTM D3041in which specimen under strain is exposed to ozone atmosphere at 40 ˚C.

Tests for Performance:

1. Flexibility-Flat loop method (IS 7016-7)

Rectangular strip of 600 ×100 mm is cut and a loop is formed by superimposing the ends of strip and placed on a horizontal plane with superimposed ends held under a steel bar. The height of loop is measured. The lower the loop height, higher will be the flexibility and vice versa.

2. Resistance to water penetration (ASTM D 751, BS 3424)

In Mullen type hydrostatic tester a specimen undergoes a hydraulic pressure on the underside. Steadily increasing pressure is applied on the specimen and the pressure is noted when water first appears through the specimen. Alternatively a specified pressure is applied on specimen for 5 minutes and appearance of water is noted.

3. Air pemeabiltiy (BS 3424)

The air permeabiltiy is determined by sucking air through test specimen. The specimen is held between two flanges having an orfice of 25 mm diameter and air is sucked through it by a vacuum pump. The rate of air flow is adjusted by valves, bypass valves. The rate of flow of air through specimen is measured by an appropriate ratometer.

4. Low temperatue bend test (ASTM D 2136)

This test is for evaluation of flexing behavior of coated textile at low temperature. Three test specimen of 25 × 100 mm are cut and placed between pair of glass plates after conditioning and is kept at low temperature. The sample is then mounted on a platform tilted at 60˚. Sample is folded to 180˚ through a free weight release mechanism and is examined for cracks and damages.