High Density Polyethylene
Low Density Polyethylene
NOTE: The data presented above is a general average. The data may vary according to polymer thickness and fabrication. The recycling symbol with a "7" is used for all other types of polymer, not just polycarbonate.
Clarity refers to both the transparency and haze of the plastic. Transparency and Haze are typically tested using ASTM D1003 standard and expressed in percentage. Plastic that have a high transparency are considered clear or transparent while those with a low transparency are considered opaque. A transparent material but with a high haze will be considered hazy or translucent. The clarity always refers to the material in its natural color without added pigmentation.
The moisture vapor transmission rate (MVTR) or water vapor transmission rate (WVTR) measures the passage of water vapor through a substance. The results vary depending and on the ambient temperature and the relative humidity. A MVTR result without specifying these conditions is meaningless. However, most tests use the ExxonMobil standard of 37.8°C (100°F) and 90% RH. It is usually measured in g/m2/day or g/100in2/day. The lower the result, the better the barrier. In pharmaceutical or alimentation bottling, a good barrier is required so humidity won’t affect the product. That is why product such as milk or juice use HDPE bottles instead of Polycarbonate or PET bottles like water.
The oxygen transmission rate (OTR) or oxygen permeation measures the passage of oxygen through a substance. The results vary depending and on the ambient temperature and the relative humidity. An OTR result without specifying these conditions is meaningless. It is commonly tested using the ASTM D3985 or ISO 15105 standards. Permeability due to diffusion is usually measure in SI unit of mol/(m²·s·Pa) but there are several units of measure used to express the results depending if it is expressed in imperial or SI units and if it has been normalized to thickness and/or pressure or not. When comparing results, it is important to make sure the same conditions and unit of measure are used. The lower the result, the better the barrier. In pharmaceutical or alimentation bottling, a good barrier is required so oxygen won’t affect the product. That is why product such as milk or juice use HDPE bottles instead of Polycarbonate or PET bottles like water.
The heat distortion temperature or heat deflection temperature (HDT, HDTUL or DTUL) is the temperature at which the polymer will bend a specified distance under a specified pressure. It is usually tested following the ASTM D648 standard or ISO 75 standard. The test is made by putting a load of either 0.45 MPA (66 psi) or 1.80 MPA (261 psi) on a specimen and lowering it in a silicone oil bath where the temperature is raised 2°C (35.6°F) until it deflects 0.25mm (0.009in) for ASTM, 0.32mm (0.012in) for ISO flatwise and 0.34mm (0.013in) for ISO edgewise. The dimensions of the specimen used are 5in x 0.5in x 0.25in (127mm x 12.7mm x 6.35mm) for ASTM, 80mm x 10mm x 4mm ( 3.15in x 0.39in x 0.16in) for ISO flatwise and 120mm x 10mm x 4mm ( 4.72in x 0.39in x 0.16in) for ISO edgewise.
The rigidity or stiffness of a polymer is described by an elastic modulus that measures a material ability to bend or be deformed elastically or non-permanently when a specific force is applied. It is measured as a ratio of stress to strain. Specifying how the stress and strain are to be measured, including directions, allow for different types of elastic moduli to be defined. The ones most often used for plastic are Young’s Modulus and Flexural Modulus (ASTM D790). The result is typically expressed in Pa or psi. The higher the result the stiffer the material. This property is also sometime expressed as flexibility, but it is measured the same way. The lower the result the more flexible the polymer is.
Environmental Stress Cracking (ESC) is a form of degradation that breaks the secondary linkage between polymers and is caused by the simultaneous action of stress and chemical. The environmental stress crack resistance (ESCR) is tested by using the ASTM D 543 or ISO 220088-3:2008 standards. The tests verify any changes in weight, appearance or tensile properties of the test specimens versus the control specimen. The results are not measured by a unit of measures but rather a series of observation such as swelling, decomposition, crazing, cracking and/or change in physical properties.
Cold resistance is based on the brittleness temperature of the plastic. It measures the temperature at which the polymer can be brittled by a specific impact condition. It is typically tested using ASTM D746 or ISO 974 standards which require 50% of the tested specimens to show evidence of brittle failure. Brittle failure can be defined by the specimen fracturing in 2 or more pieces, or showing any cracks visible to the unaided eye. The lower the temperature, the better the resistance.
The impact resistance measures the amount of energy needed to notch the plastic of a specific thickness. It is commonly tested using the Izod impact strength test following the ASTM D256 standard or ISO 180 standard. The result can either be expressed by energy lost by unit thickness (ft·lb/in or J/cm) or energy lost per unit cross-sectional area at the notch (ft·lb/in² or J/m²). Most test use the ASTM standard thickness of 3.2mm (0.13in). The higher the result, the better the resistance to impact.