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How to determine Seam Strength

Seam strength is the strength of seam assembly in a garment. It is a function of the strength ofthe thread used for the seam, type of seam assembly in a garment and type of fabric

used, among other factors.

Failure of seam assembly can occur either by breaking of sewing thread, tearing of the fabric at

the seam, excessive yarn slippage adjacent to the stitches or a combination of the above

mentioned conditions.

How to determine seam strength in laboratory

In a lab CRE type tensile testing machines such as INSTRON is used. Before testing the samples

are prepared.The method is called Grab Test

If the specimens are from manufactured items such as garment then five speicmens are cuthaving a length of 270 mm on either side of the stitch line and a width of 100 mm parallel to the

stitch line.

If the specimens are prepared from fabric then seam strength is measured in warp, weft and bias

directions. In such cases swatches are cut in these three directions.

Also two such swatches from two different rolls are joined by the seam assembly- for which we

want to test the strength- to measure the parameters.

Before testing the material is conditioned to standard temperature.

The specimen is mounted on the tensile tester. It is operated until the sewn seam or fabric

ruptures. The observation is made whether the rupture is caused by Fabric yarn rupture, sewingthread rupture, sewn seam yarn slippage or a combination of two or more of the foregoing. This

will give the seam strength.

Repeat this Grab Test for the fabric specimens from which seam failure test is carried out. The

result will give the base fabric strength.

Seam strength ( for each direction) will be calculated by the formula:

Seam strength ( gms/cm)= ( Individual specimen seam breaking force in gms)/ Width ofspecimen in Jaws i.e. 2.5 cm.

Base fabric breaking strength of the individual specimens are calculated by the formula:

Base fabric strength (gms/cm)= (Base Fabric breaking force in gms of individual testspecimen)/ Width of specimen in jaws i.e. 2.5 cm

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Seam Efficiency= Seam Strength ( Seamed Fabric Strength) x 100)/ Base Fabric Strength

If this seam efficiency ratio falls below 80%, the fabric has been excessively damaged by the

sewing operation.

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Labels:Seam strength,textile testing

Manufacturing Process and Properties of PVA

Polyvinyl Alcohol Fibres

Polyvinyl alcohol (water soluble compound) can be described as a polyhydric, having secondary

alcoholic groups on alternate carbon atoms of an aliphatic macromolecule.

Because of the presence of a large number of hydroxy groups, in its molecular structure, it issoluble in water. This is solublised in water by a treatment with formaldehyde.

Manufacture of Polyvinyl Alcohol

1. Production of acetic acid from acetylene

For this purpose, limestone is calcinated to give quicklime (CaO) which is treated with coke atelevated temperature to form calciium carbide. Acetylene is generated by treating calciumcarbide with water. A part of acetylene is converted into acetic acidby combined hydration and

oxidation.

Synthesis of Vinyl Acetate

The acetic acid formed in the above step is reacted with acetylene in the presence of zinc acetatecatalyst when vinyl acetate is formed.

Polymerisation of Vinyl Acetate

A solution of vinyl acetate in methanol is used for the polymerisation of vinyl acetate in the

presence of a peroxide or azo compound as a catalyst.

Conversion of PVAcetate into PVA

NaOH is added in PV Acetate solution in methanol, when alcoholysis of the acetate groups takes

place.

Spinning

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The precipitated PVA as obtained in the preceding step is pressed and dried. It is then dissolved

in water to give a 15% solution of the polymer. This solution is extruded into a spinning bathcontaining sulphuric acid ( 20%), Glauber's Salt ( 25%), formaldehyde (5%) and water (50%)

Properties

Shrinkage Properties: 10% at 220-230 deg C.

At 220 deg c, It begins to turn yellow and shrinks.

The fiber is inert to animal, vegetable and mineral oils and to most common organic solvents.

It has good resistance to acids under normal conditions, Hot or concentrated mineral acids cause

swelling and shrinkage. Its resistance to alkali is generally good. Strong alkalies cause yellowing

without affecting the tenacity.

Fabrics made from this fibre do not get solied easily. They are easy to wash and quick to dry.They have good crease retention.

Specific Gravity: 1.28

Staple Filament

Tenacity ( GPD)

Dry 3.8-6.2 6.0-8.5

Wet 3.2-5.0 5.0-7.6

Elongation at BreakDry 13-26% 9-22%

Wet 14-27% 10-26%

Elastic Recovery 65-85% 70-90%

Moisture Regain 4.5-5% 3-5%