Hand protection. Aramid and other materials for protective gloves

Gloves with cut protection are necessary for any intensive work with knives and sharp tools, in particular when sharpening knives. To protect the hands from cuts, gloves are used with the most durable types of materials that can withstand loads not only on the cut but also on the puncture, tear, and abrasion. The main materials used for such gloves are aramid, Dyneema fibers, as well as a mixture of these materials with glass fiber and metal threads.

Aramid

The material aramid is a so-called aromatic polyamide  – a long chain of synthetic polyamide, that is, plastics based on linear synthetic molecular compounds containing amide groups −CONH−in the main chain. The properties of polyamide-derived fibers are determined simultaneously by the chemical and physical microstructure. Amide bonds provide high dissociation energy, i.e. chemical bond strength and increased thermal stability.  In total, there are three types of aramid fibers used in the industry: para-aramids (p-aramids), meta-aramids (m-aramids), and polyamide copolymers. 

The world's most famous para-aramids are produced under the brand names Kevlar and Twaron. Commercially produced Kevlar 29, Kevlar 49, and Kevlar fibers have a large elastic modulus and large forces are required to break such a fabric: from 250 to 600 kg per square millimeter. Kevlar has a density of 1400-1500 kg/m3, which is almost 2 times lighter than fiberglass. An important property of this material is that it is practically not subject to burning and melting at high temperatures. Besides, Kevlar fibers are an electrical insulator and are hardened in the cold, allowing the use of fabric products in the most severe climatic conditions. Kevlar is characterized by softness, hygroscopicity, and the ability to air exchange. All these properties are caused by the use of para-aramids as a cord for tires, as well as various ballistic and composite materials. The highest strength allows you to resist bullet impacts and is used in the manufacture of bulletproof vests.

For all its advantages, aramid also has obvious disadvantages: it can not be cleaned with chemical reagents, exposed to sunlight. When wet, the strength of the aramid fiber is reduced by almost 2 times, and when dried, it is not fully restored, besides, aramid ages very quickly and loses its properties within 10 years from the date of manufacture. But the main disadvantage of this material is of course the high price. Therefore, gloves that protect against cuts are most often made not entirely from kevlar, but from fabric reinforced with kevlar threads. Gloves made on the basis of aramid reliably withstand the cutting blow of a knife and not a heavy cutting blow. But, as well as other similar gloves are not able to withstand a piercing blow. And while a thick aramid bulletproof vest can withstand a stab, a thin glove can't.

Dyneema fibers 

Ultra-high molecular weight polyethylene ( HPPE) is a thermoplastic polymer, a structural material used to work in extreme operating conditions. The HPPE molecule consists of long linear chains of polyethylene with relatively weak intermolecular bonds. This distinguishes HPPE from aramid, which has short molecules and strong molecular bonds. In Europe, HPPE fibers are known under the brand name Dyneema, in the United States - Spectra.

HPPE products are obtained by the following processing methods:

Pressing;

Continuous profile pressing, or extrusion

Gel-forming;

Plunger extrusion.

It is with the help of gel-forming that the most durable fibers of the Dyneema and Spectra brands are obtained for cables, slings, for use in ballistic protection, in the field of defense technologies.

In the production process, the plastic mass of HPPE is dissolved in decalin and then squeezed into an aqueous solution, and the resulting gel is pulled out at a temperature of about 100 degrees while removing the solvent. During the forming process, molecules consisting of long linear chains of polyethylene are twisted into fibers, and lose intermolecular bonds. As a result of this process, the orientation of the molecules becomes parallel, and due to the high molecular weight, the fibers become strong, inextensible, neutral to aqueous and chemical solutions, get high wear resistance, UV resistance, and low weight.

When comparing Dyneema fibers with kevlar, the first ones benefit from many characteristics. In particular: in terms of tensile strength, resistance to ultraviolet radiation, and most importantly, resistance to wetting, which significantly reduces the strength qualities of aramid and does not affect the properties of high-modulus polyethylene fiber at all.

It is made of HPPE material that TSPROF gloves are made, which have 5-class cut protection according to the European standard DIN EN 388: 2003.

Mechanical risks and their test methods are defined in DIN EN 388: 2003 according to the following criteria:

1. The abrasion resistance

It is checked by processing the glove with sandpaper under pressure. The number of cycles required to rub a hole in the material serves as a reference. The maximum level is considered to be 8000 cycles.

2. Resistance to cut

It is determined by the rotation of a circular blade that cuts through the glove at a constant speed. After that, a comparison with the sample material serves as a reference and the resulting index. The maximum index is 20.

3. Tear resistance

To test the tear resistance, the glove material is first cut. The force required to break the material serves as a sample. The maximum efficiency level is 75 Newtons.

4. Resistance to puncture

To measure the resistance to puncture, the glove is punched with a nail of a certain size. The force used serves as a sample. The maximum efficiency level is 150 Newtons. This test only tests the strength of the fabric itself, but not the ability of the glove to protect the hand from injury. Gloves can not protect against a stabbing blow and even if the fabric can withstand the pressure, the person's hand will still be injured. 

Synthetic fibers mixed with fiberglass and metal threads

To increase the reliability of gloves from cuts, the technology of mixing aramid or high-molecular polyethylene fibers with glass fiber and metal threads is used. In particular, in such gloves, a base of 55% HPPE (molecular polyethylene), 20% nylon, 15% fiberglass, 10% spandex, with a coating of 100% polyurethane can be used. The gloves can be made in the technology of platinum knitting - a smooth HPPE thread is placed on the inner side of the glove, which is in contact with the skin, which gives additional comfort when working. The 100% polyurethane coating of the palm and fingertips improves grip and extends the life of the gloves. The backside of the gloves is often left without coverage that allows the skin to breathe.

Another technology is the sewing of metal threads into the fabric. Stainless steel, glass fiber, polyester, and polyamide fibers are added to the base of high-molecular polyethylene fiber HPPE. These gloves are made seamlessly and provide comfortable wear and mobility of the hand.

Gloves from cuts are certainly necessary for everyone who works with sharp objects for a long time and, in particular, sharpens knives. Cuts are always a big danger for the sharpener and such gloves are an important element of safety.