PROPERTIES OF PACKAGING MATERIAL

Contents• Tensile strength• Bursting strength• Tearing resistance• Puncture resistance• Impact strength• Tear strength• Permissibility (GTR, WTR)• shelf life of products, selection and designing

Tensile strength

• Tensile strength is the ability of a material to resist a direct pull. When referring to ultimate tensile strength, it is the maximum stress that can be withstood before breaking. Commonly the tensile strength is expressed in pounds per square inch.

• Typically noted in either pounds per square inch (psi) or megapascals (MPa)

MACHINE USED:• Universal testing machine

calculation• Tensile strength (nominal), max. load kg/cm2 = original min. cross sectional area of specimen

• Tensile strength (at break), max. load at break

kg/cm2 = original min. cross sectional area of specimen

• Breaking factor (nominal), max. load

kg/cm2 = original thickness of specimen

For paper: tensile strength is reported as Kgf/cm

BURSTING STRENGTH• It is the hydrostatic pressure in pounds/inch2 (kg/cm2

• A property of paper or paperboard used in packaging that measures its resistance to rupturing, defined as the hydrostatic pressure needed to burst a paperboard sample when it is applied uniformly across its side

• MACHINE USED:

• Bursting strength tester

Calculation:• Busting Strength(Kg/cm2)= Bust Factor(B.F)*GSM(Gm/m2)/1000

• Burst factor= bursting strength((Gm/m2)• grammage (gm/m2)

Tearing resistance• is a measure of how well a material can withstand the

effects of tearing.• Noted in kilonewtons per meter (kN/m) or pound force per

inch (lbf/in)• MACHINE USED

ELMENDORF TEAR

TESTER

CALCULATION

R= S*C n

R= tear resistance in gramsS- corrected scale readingC= machine capacity in gramsN= Number of sheets in each test

PUNCTURE RESISTANCE1.Puncture resistance is a measure of the maximum force

or energy required to penetrate a material. This type of biaxial stress is seen by packaging films when packing hard protuberances such as pelleted dry foods and frozen vegetables.

• MACHINE USED: puncture resistance tester

CALCULATION

IMPACT SRENGTH• is the capability of the material to withstand a suddenly

applied load and is expressed in terms of energy.• Volume, modulus of elasticity, distribution of forces, and

yield strength affect the impact strength of a material.• MACHINE USED• Izod impact testing machine

calculationThe impact strength is calculated as the ratio of impact absorption to test specimen cross-section

Impact absorption: test specimen cross section

Permissibility • GAS TRANSMISSION RATE:

OTR,” is the steady state rate at which oxygen gas can permeate through a film. 

OTR is expressed as a volume of oxygen that penetrates a given area in a one-day period; cc/m2/24hr…or…cc/100 in2/24hr, measured at a standard temperature of 73°F (23°C), and 0% relative humidity (RH). 

General comparisons of barrier capabilities are as follows:

Relative OxygenBarrier Capability

cc/m2/24hrs cc/100 in2/24hr

High Barrier ~ 1-10 ~ 0.06-0.65

Moderate Transmitter (of O2) ~ 1000 ~ 64.50

High Transmitter (of O2) ~ 10,000 ~ 645.20

Water transmission rate• WVTR), often referred to as “moisture vapour transfer rate” (MVTR), is the

standard indicator of how easily moisture can permeate a packaging film.• Its values expressed as g/m2 and g/100in2 at 38°C and 98% relative humidity.• Increasing WVTR values indicate greater permeability, and lower ability to

keep dry products dry, and moist products moist. 

• Factors affecting WVTR values include…• Thickness• Resin Composition

• Molecular weight distribution• Crystallinity/density• Chain-length and chain-length distribution• Chain orientation

• Polymer blends• Additives• Coatings – PVdC, metalizing• Processing Parameters – BUR, frost-line height, die gap

SHELF LIFE OF PACKAGED FOODS

• Shelf life is the length of time that a commodity may be stored without becoming unfit for use or consumption. The test that determine the shelf life of products are:

1. Moisture content of the products.

2. The moisture content of the product at the which the product becomes unacceptable to the consumer

3. The RH and the temp of the surrounding atmosphere at which the equilibrium moisture content is maintained in the product.