Test of packaging materialPurpose of testing packaging material1. Selection of packaging material2. Comparison of two or more different packaging materials3. As an aid in designing of package4. Assure quality and conform specificationIn overall we test packaging material to see its whether it has the required functions.

1. Tensile Strength:It is a measure of films resistance to being pulled apart at a constant rate of speed.Maximum load that a material can support without fracture when being stretched, divided by the original cross-sectional area of the material. Tensile strengths have dimensions of force per unit area and in the English system of measurement are commonly expressed in units of pounds per square inch, often abbreviated to psi. When stresses less than the tensile strength are removed, a material returns are either completely or partially to its original shape and size. As the stress reaches the value of the tensile strength, however, a material, if ductile, that has already begun to flow plasticity rapidly forms a constricted region called a neck, where it then fractures. Tensile properties are an important and common way to compare physical properties of diverse materials, from steel to plastic. In the narrower realm of flexible films, these tests provide measurement of attributes we can see and feel: strength, stiffness, and resistance to stretching. The tensile strength of polypropylene increases significantly by the orientation process. Resin selection and orientation method are the primary variables that influence tensile values. Therefore, tensile properties are almost entirely defined by product design itself. Small variations in tensiles will inevitably result due to normal process variation, but the performance effect is insignificant.Test principlesEach end of a film specimen, of specific width and measured thickness, is held by a clamp or grip. One grip is stationary, while the other is pulled away from the first at a pre-selected velocity. The machine continuously measures the changing distance between the grips and the force exerted on them as they pull the film apart. The test is completed when the sample breaks.Today, most machines run automatically after the operator selects settings, loads the specimen, and initiates the test. Most are also equipped with microprocessors that perform the calculations and automatically display all the resulting values. But, the test concepts are best understood by studying load-extension curves like the ones shown in Graph 1. These are actual machine direction (MD) and transverse direction (TD) load-extension curves for a typical, tender-oriented, 75 gauges OPP. In Graph 1, load is plotted as a function of extension, and the tensile tester software calculates the following properties that are noted in Table 4.

Graph 1: Typical OPP load-extension curvesTable 4: Tensile values from Graph 1Results

SampleDescriptionThickness (mil)UltimateStrength (kspi)Modulus (kpsi)Elongation (%)

1MD pull.7518.9343174

2TC pull.7539.368745

Table 4 values are software-generated results based on the following equations.Ultimate Tensile Strength (psi) =Max Load (lbf)=Max Load (lbf)

Initial cross-sectional area1 in x .00075 in

Modulus (psi) = At any point on the elastic region tangent line (Stress Strain) =Load (lbf)Extension (in)=Load (lbf)Extension (in)

Initial cross-sectional areaInitial grip separation.00075 in22 in

Elongation (%) =Extension at failure x 100=Extension at failure x 100

Initial grip separation2 in

Test conditions like pull speed, initial grip separation, full-scale load, and sample width will affect the results. Tensile properties can change with small changes in temperature; so it is important to conduct tests in a controlled environment. Standard laboratory temperature is 72F (22C) 2F (1C).Other factors affecting the tensile strength are the composition of material, method of processing, type of packaging material, their physical properties and Machinability.Tensile strength is a most important value for materials used in applications such as heavy-duty bags. A large value for elongation is an index of toughness, since it indicates a material will absorb a large amount of energy before breaking.

An instrument called Good Brand Tensile Tester is used for this purpose. The specimen is clamped between jaws and pulling force is applied. The force at which the specimen breaks is noted as kg/15mm. Elongation is a strength property. It is measured by the same instrument on a calibrated scale (having a pointer) and the result is expressed as:% Elongation = (reading100) / (2 inch)A schematic diagram of the instrument is given below:

Dynamic Tensile StrengthThis measures the energy required to break a specimen of specified dimension by subjecting it to an impact stress. The paper is clamped in a sigmoid shape. A pendulum is released to cut the paper. This test is important for construction of multiwall paper bags as it gives an index to the capacity of the sample to absorb impact shock.InstrumentVan der Korput Baarn Tensile Tester is used for this purpose. The specimen is clamped between jaws in sigmoid shape. The pendulum is released and the impact (kg.cm) as registered on the scale is noted.

2. Tear resistanceIt is the force necessary to continue tearing a sample after a nick has been made. This test is very important for all films as well as for paper. High tear values may be needed for machine operations or for package strength. However, low tear values are necessary and useful for easy opening of some package types. Tear strength is reported in grams. A tear tester has a stationary clamp and a movable clamp on a pendulum, means for holding this pendulum in a raised position, then quickly releasing it, and a scale that registers the arc through which the released pendulum swings. Samples of paper or film are clamped into the tester and nicked to start the tear; then the pendulum clamp is released. This tears the sample and the scale registers the arc. As the arc is proportional to the tear strength of the sample, calibration of the arc gives the tear strength.Tear test is of two types edge tearing and internal tearing. Internal tearing is mostly frequently used for measuring the tear resistance of papers and plastic films. The tear resistance depends on the type of packaging material, physical properties, processing method and the condition of testing.An instrument named Tear-ASTM-D-1922 is most widely used for measuring tear resistance.2. Resistance to abrasionThis test is done to measure the ability of a packaging material to withstand surface wear during rubbing and friction. The test consists of abrading the sample with a wheel of standard abrasion pad (abradant) for a definite number of revolutions and finding its volume loss.Volume loss = weight loss/specific gravity.3. Drop testDrop Test: The test simulates actual shocks by dropping the package and its content freely against a rigid plane surface from a predetermined height. For example, a drop test can be conducted so that the package hits the surface diagonally against one corner, as in the picture beside.

Fig: Drop testing of a box

4. Stack load testThe Compression/Stacking Tests: This test is performed to assess the ability of a transport package to withstand compressive forces and to protect its contents during compression. The test may also be used as a stacking test to investigate the performance of i.e. the bottom package in a stack during storage in a warehouse.The test is carried out by stacking the packaged material above one another or by placing a fixed weight above the unit pack for a certain time. It can also be done by compressing a pack from two opposite sides and measuring the pressure applied to break/deform the container.

Fig: compression testing of a wooden box.

This test is generally applicable in case of wooden box, paper box, paperboards, cans and other secondary packaging material. This property is also important for finding the stacking height in a warehouse.

5. Vibration test The Vibration Test: Various forms of transportation vibrations can be simulated in a laboratory through a vibration test. The test-bench can be made to swing and vibrate in almost any direction with a number of frequencies and amplitudes to emulate the transportation being used.Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration testing is accomplished by introducing a forcing function into a structure, usually with some type of shaker. Alternately, a DUT (device under test) is attached to the "table" of a shaker. For relatively low frequency forcing, servo-hydraulic (electro-hydraulic) shakers are used. For higher frequencies, electro-dynamics shakers are used. Generally, one or more "input" or "control" points on the DUT are kept at a specified vibration level. Other "response" points experience maximum vibration level (resonance) or minimum vibration level (anti-resonance).Two typical types of vibration tests performed are random- and sine test. Sine (one-frequency-at-a-time) tests are performed to survey the structural response of the device under test (DUT). A random (all frequencies at once) test is generally considered to more closely replicate a real world environment, such as road inputs to a moving automobile.Most vibration testing is conducted in a single DUT axis at a time, even though most real-world vibration occurs in various axes simultaneously. MIL-STD-810G, released in late 2008, Test Method 527, calls for multiple exciter testing.6. Overall migration testa. Water vapor transmission rateb. Gas transmission rate

Water vapor transmission rate(WVTR)DefinitionWVTR (water vapor transmission rate) is the steady state rate at which water vapor permeates through a film at specified conditions of temperature and relative humidity. Values are expressed in g/100 in2/24 hr in US standard units and g/m2/24 hr in metric (or SI) units. Test conditions vary, but ExxonMobil has standardized to 100F (37.8C) and 90% RH, which is the most common set of conditions reported in North America.Relevance to package performanceA critical function of flexible packaging is to keep dry products dry (potato chips, pretzels, fortune cookies...) and moist products moist (cheese, muffins, chewing gum...). Without protective packaging, products will quickly gain or lose moisture until they are at equilibrium with the environmental relative humidity. At this point, crispy products are soggy, and chewy products are hard and dry.WVTR is the standard measurement by which films are compared for their ability to resist moisture transmission. Lower values indicate better moisture protection. Only values reported at the same temperature and humidity can be compared, because transmission rates are affected by both of these parameters.The order of water vapor resistivity in films of 1 mm is as follows, BOPP > HDPE > cast PP >BPET >LDPE>EVOH at 100F (38C), 90% RH for 1 mil filmWhat affects the WVTR of OPP films ?The most obvious factor that impacts WVTR is thickness: if an OPP of the same product design is twice as thick as another, its WVTR will be half the value. This is so because WVTR is an inherent, bulk film property of OPP.It is common to find variation in the reported WVTR values for same-gauge OPP films produced or measured by different manufacturers. The primary factors causing these differences are:1. Raw material: Homopolymer PP resin differences in average molecular chain length, range of chain lengths, and degree of crystallinity can account for up to a 10% difference in WVTR. Additives and copolymer resin layers can account for differences of up to 30%. 2. Process: Normal differences in process conditions between one orienter and another account for about 5% variation in WVTR values. (WVTR is reduced through orientation, because the crystalline regions of the polymer matrix are aligned. In other words, orientation efficiently "packs" polymer chains, so that larger spaces are minimized. Process conditions affect this "packing," and therefore, WVTR values.) 3. Measurement: The instrument manufacturer, MOCON,states a test precision of :t3% with their PERMATRON-W product line. Therefore, trained operators using this type of instrumentation will generate values from .34 to .36 when testing a 1 mil OPP with a nominal WVTR of .35 g/100 in2/24 hr. Test principlesExxonMobil test cell looks like Figure below. Dry nitrogen gas is swept through a chamber where the test film acts as the membrane separating this dry gas stream from a "wet" nitrogen stream on the other side. The partial pressure difference creates a driving force for the water vapor to permeate through the film to the low pressure side. The barrier of the film determines how much water vapor can transfer, and this is continuously measured by an infrared detector in the outgoing stream of the dry side.

Figure 3: Cross-section of a WVTR test cellThe test is complete when equilibrium, or steady state, is achieved, which is when the infra-red sensor detects water molecules leaving the dry chamber at a constant rate. The amount of water vapor permeating through the sample per unit time period is not changing. This rate is the sample WVTR and is recorded in units of g-H2O/100 in2/24 hr at 100F (37.8C), 90% RH.

Oxygen transmission rateDefinitionOTR (oxygen transmission rate) is the steady state rate at which oxygen gas permeates through a film at specified conditions of temperature and relative humidity. Value are expressed in cc/100 in2/24 hr in US standard units and cc/m2/24 hr in metric (or SI) units. Standard test conditions are 73F (23C) and 0% RH.Relevance to package performanceThe air we breathe is about 21% oxygen and 79% nitrogen, with very small concentrations of other gases like carbon dioxide and argon. Essential to human and animal life, oxygen gas is also a reactive compound that is a key player in food spoilage. Most of the chemical and biological reactions that create rancid oils, molds, and flavor changes require oxygen in order to occur. So, it is not surprising that food packaging (and some non-food packaging for products where atmospheric oxygen causes harm) has progressed and found ways to reduce oxygen exposure and extend the shelf life of oxygen-sensitive products.There are two methods for reducing product exposure to oxygen via flexible packaging.1. MAP (modified atmosphere packaging) is a process for replacing the air in the headspace of a package with another gas before the final seal is made. This is also called gas flushing. The most common replacement gases are nitrogen or nitrogen/carbon dioxide mixtures. The shelf lives of potato chips, dried fruits, nuts, and shredded cheese are commonly extended by this packaging method. 2. Vacuum packaging is where the atmosphere is drawn out and eliminated, rather than being replaced by another gas. This vacuum forces the flexible material to conform to the product shape. Meats (fresh and processed) and cheeses are commonly packaged this way. Once air has been replaced or eliminated from the package, there must be an adequate oxygen barrier and seal integrity to keep a low oxygen concentration inside the pack. Otherwise, the driving force created by the oxygen partial pressure differences (21% outside the bag and 0-2% inside the bag) will cause an ingress of oxygen and destroy the benefit of removing it in the first place. OTR values are used to compare the relative oxygen barrier capabilities of packaging films. An industry rule-of-thumb is that a material is considered a "high oxygen barrier" if its OTR is less than 1 cc/100 in2/24 hr (15.5 cc/m2/24 hr).Table 10 shows OTR values for common polymer packaging films. Note that the table is divided into two sections. The first contains normalized (1 mil) values for common materials. The second section displays the OTRs for coated or metallized films where the total film thickness is unimportant, because the barrier is primarily coming from the additional layer.Generally asked question: Many customers ask about the carbon dioxide (CO2) and nitrogen (N2) transmission rates through film. ExxonMobil does not perform transmission testing with these gases, but a value range can be estimated from OTR values by using the following relationships. CO2 TR will be 3 to 5 times the OTR value at 73F (23C), 0% RH N2 TR will be .2 to .4 times the OTR value at 73F (23C), 0% RH For example, the OTR of 110 AXT is .40 cc/100 in2/24 hr @ 73F (23C), 0% RH. Therefore, at the same conditions, the CO2 TR is approximately 1.2 - 2.0 cc/100 in2/24 hr and the N2 TR is approximately .08 to .16 cc/100 in2/24 hr.What affects the OTR of filmsGood oxygen barrier is achieved by combining functional layers to create a film with the required barrier, as well as those other properties necessary to produce a serviceable package. For example, EVOH has exceptional OTR properties, but needs moisture barrier and mechanical properties provided by layers that are coextruded or laminated around it.OTR is most affected by the following factors.1. Thickness of barrier layer: Generally, the thicker the oxygen barrier-providing layer, the better the barrier. But there are process and cost limitations that restrict the thicknesses that can be realistically produced or successfully utilized. 2. Copolymer ratio, plasticizer content, and polymerization process: All PVdCs (or EVOHs or PVOHs) are not created equal. Properties are compromised during polymer and product development, so that total performance in target applications is optimized. There can be substantial differences in OTR values depending on the selections made. For example, both ASB-X and AXT are PVdC-coated and sealable, but their OTRs are 4.5 cc/100 in2/24 hr and .40 cc/1 00 in2/24 hr, respectively. ASB-X has the poorer OTR, but a broader seal range than AXT. 3. Base film surface compatibility: The physical and chemical characteristics of the base film surface have a major effect on the OTR after metallization, and to a lesser degree, after coating. This is evidenced by Met PET's exceptional barrier, as well as the difference in OTRs between various metallized OPP products Test PrincipleConceptually, a test cell looks like Figure 4. Dry nitrogen gas is swept through a chamber, where the test film acts as the membrane separating this stream from an oxygen stream on the other side. The partial pressure difference creates a driving force for oxygen molecules to diffuse through the film to the low pressure side. The film barrier determines the rate of oxygen permeation, and this is continuously measured by a MOCON patented coulometric sensor in the outgoing ,stream of the nitrogen side. The standard test conditions are; 73F (23C) and 0% RH.

4. Figure 4: Cross-section of an OTR test cellThe test is complete when equilibrium, or steady state, is achieved; that is, it is complete when the sensor detects a constant amount of oxygen in the nitrogen carrier stream. The rate of oxygen permeating through the sample is not changing. This rate is the sample OTR and is recorded in units of cc/100 in2/24 hr or cc/m2/24 hr at 73F (23C), 0% RH.It is important to discuss the effects of relative humidity on OTR, even though the ASTM standard procedure is at dry conditions. Relative humidity has a dramatic and negative effect on the OTRs of some materials, most notably nylon, EVOH and PVOH. The effect is especially pronounced at RHs over about 70%.Film TypeOTR @ 73F (23C), 0% RH

(cc/100 in2/24 hr)(cc/m2/24 hr)

The following OTRs are bulk material properties displayed at 1 mil. You may divide by the gauge (in mil) in order to approximate OTR at a different thickness.

EVOH* (ethylene vinyl alcohol).005 - .12.08 - 1.9

Biax Nylon-61.2 - 2.518.6 - 39

OPET (oriented polyester)2 - 631 - 93

OPP100 - 1601550 - 2500

Cast PP150 - 2002300 - 3100

HDPE (high density polyethylene)150 - 2002300 - 3100

OPS (oriented polystyrene)280 - 4004350 - 6200

LDPE (low density polyethylene)450 - 5007000 - 8500

7. Optical test-gloss-opacity-haze-light transmission-optical densitya. Gloss:Gloss is a measurement of the relative luster or shininess of a film surface. ExxonMobil uses 45-degree gloss, where the incident light beam strikes the film surface at a 45 degree angle from the perpendicular. A sensor measures the amount of light reflected by the film at a mirror image angle. The gloss value is the ratio of this reflected light to incident light and is reported in gloss units. Theoretically, the range of the gloss scale is 0 to 100.Shininess, brilliance, and sparkle are properties related to a film's gloss value. They can be valuable appearance attributes for packages, labels, or graphic arts items.Precise comparisons of gloss values can only be made when the measurements are performed on samples of the same general type of material, using the same procedure and test angle. In particular, it is not valid to compare the gloss values of transparent films and opaque films.What affects film gloss Gloss is primarily determined by material selection and surface smoothness, which are defined during product and process development. Day-to-day process variations will have an insignificant effect on gloss. Transparent films have two reflecting surfaces. Although rare, this can lead to gloss values that exceed 100.Test principlesExxonMobil uses commercially available gloss meters to measure 45-deg gloss consistent with ASTM procedure D 2457. The simplified diagram in Figure 2 graphically summarizes the test.

Figure 2: Gloss measurementb. OpacityDefinitionOpacity represents a substrate's light blocking ability. It is primarily used as a property of paper and predicts the relative visibility on one side of the paper of the images that exist on the other side. Because white opaque films are replacing paper in some applications, ExxonMobil measures opacity for some white films.There are two common types of opacity measurements, and ExxonMobil uses the one called "89% reflectance backing," also called "contrast ratio." This value is equal to 100 times the ratio of the diffuse reflectance of a film sample backed by a black body (