TENSILE  &  MECHANICAL PROPERTIES

Measure strength, toughness, elongation, yield point, elasticity (modulus), break energy.

Strips of film are clamped in the jaws of an Instron computer-controlled universal test instrument and stretched at a constant speed until they break.

​Separate tests are done in the machine and transverse directions (i.e. length and width ways).

The force and extension are graphed and the above properties are calculated.

ASTM Method: D882    Usual Units: as defined by ASTM standards. 

Application: Plastic films and thin sheeting. Maximum force capability 2000N or 200kg force.

TEAR RESISTANCE OF PLASTIC FILMS

Determines the force necessary to propagate a tear.

Rectangular strips of film 25 mm wide and 75 mm long are pre-slit down the middle for 50 mm of their length, leaving 25 mm intact. The slit strip resembles a pair of trousers. The “legs” are clamped in the jaws of a tensile tester and pulled apart, so that it tears in the line started by the slit. The test result is the maximum force registered while tearing.

Separate tests are done in the film’s machine and transverse directions.

​ASTM Method: D1938     Usual Units: N     Application: Plastic films and sheets

PUNCTURE RESISTANCE OF PLASTIC FILMS

Measures the resistance of a film to probe penetration.

The film is held in a clamp with a 100 mm diameter opening. A probe is driven into the film until it ruptures. Puncture force, energy and stretch are recorded.

The standard probe tip diameter is 19 mm, but non-standard probe sizes are also available, including 12.7 mm diameter to simulate fingers, and 1 mm to simulate semi-sharp objects.

ASTM Method: D5748  

Usual Units: as defined by ASTM standards.

Application: Plastic films and sheets

IMPACT RESISTANCE - DART DROP OF PLASTIC FILMS

Determines a film’s resistance to impact from a weighted object falling on it.

 

The film is held in a clamp with a 127mm diameter opening. A dart with a rounded tip of 38mm diameter is loaded with weights and dropped onto the clamped film. Many drops are done, each on a fresh film area, with the dart weight increased or decreased each time according to whether or not the film ruptures. We calculate the Wf result, the theoretical dart weight at which exactly 50% of the drops would result in film rupture.

 

ASTM Method: D1709    Usual Units: grams    Application: Plastic films and sheets

Measures the weight a container can stand before distorting.

 

A bottle, tub or other container is crushed between compression plates. This measures crushing force (in Newtons) - the vertical load the container can withstand before it deforms.

 

ASTM Method: D2659     

Application: Plastic tubs, bottles and containers

The strength of heat seals influences package integrity.

We can also measure peel force of peelable seals.

ASTM Method: F88        Application: Plastic bags, liners, trays, tubs, and containers.

HEAT SEALABILITY TEMPERATURE RANGE

 

A graph of seal strength vs sealing temperature to determine optimum heat sealing temperature.

ASTM Method: F2029     Application: Plastic bags, liners, trays, tubs and containers.

BOND STRENGTH OR PLY ADHESION

The performance of a laminated material designed to function as a single unit depends on bond strength between the layers of materials.

Excessive heat or cold, fats and oils may adversely affect bond strength.

ASTM Method: F904      

Usual Units: as defined by ASTM standards.

Application: Plastic films and sheets

GunnLab Plastics Testing Pty Ltd

PO Box 403, Black Rock

VIC 3193, Australia