Glove material strength and stretch are important factors in a glove’s quality and performance. Medical and cleanroom gloves undergo testing according to ASTM D412 to meet International standards. This ensures you get a glove that is not prone to tear or fail, and has adequate stretch.
What is ASTM D412?
ASTM D412 is one of over 12,000 standards that operate globally under ASTM International. The current version of the standard is D412-06a(2013) Tensile Properties of Vulcanized Rubber and Thermoplastic Elastomers – Tension.
In this standard, glove material is measured for tensile stress (or tension,) tensile strength, yield point and ultimate elongation.
In Test Method A, a die cut “dumbbell” shaped piece of glove material is stretched from either end by a machine at a constant speed until it breaks. The computer on the machine collects the data as the piece is stretched. Once the piece breaks, the sample’s elongation is measured and recorded.
The test is repeated on samples that have been put through the accelerated aging process in heating chambers according to ASTM D573. This test simulates the glove’s physical properties at the end of its shelf life. This is a “worst case” scenario. Many gloves that have been stored properly, in a cool, dry place away from sunlight, heat and humidity, will have better strength and elongation than the “after aging” test results.
Tensile strength is measured in MPa, or megapascals. The minimum tensile strength for latex exam gloves before aging is 18 MPa, and 14 MPa after aging. The minimum tensile strength for nitrile exam gloves is 14 MPa both before and after aging.
The minimum elongation for latex gloves before aging is 650%, and 500% after aging. Nitrile gloves have a minimum elongation of 500% before aging, and 400% after aging.
Typical Performance vs. ASTM Minimums
Most gloves, however, are manufactured with much higher tensile strength and elongation properties than the ASTM minimums. The typical performance of HandPRO® RoyalTouch300™ Nitrile Exam Gloves during its shelf life, for example, is a tensile strength of 28-32 MPa and an ultimate elongation of 520 – 560%.
HandPRO® Cleanroom gloves are also manufactured to exceed ASTM minimums. HandPRO® Series 9100 Clean Class 100 Nitrile Gloves have a typical tensile strength of 27.1 – 31.0 MPa after aging, and a 540-560% ultimate elongation after aging.
Tensile Strength and Elongation in Use
So what do these numbers mean for you when selecting and wearing gloves?
While high tensile strength is preferred, the “highest” number does not necessarily mean “best” performance. Glove manufacturers must carefully balance strength with stretch and comfort. Too high tensile strength will make a glove stiff or difficult to don.
Elongation is important to the performance of the glove. High elongation helps the glove material stretch instead of tear when snagged. A glove with good elongation will stretch and conform to your hand, improving comfort and performance.