Tag Archive for: Polyurethane Soles

The Different Sole Compounds

It is a part of your safety shoe or safety boot that doesn’t get the attention it deserves. Again, a critical component that needs understanding in order to make an informed decision prior to your purchase. All shoes have a sole, which is the bottom of a shoe, the part that comes into full contact with the ground.

Modern Soles can be made from a variety of materials, but most modern safety shoes have soles made from:

  • PU (Polyurethane)
  • TPU (Thermoplastic Polyurethane)
  • Rubber soles

Prior to these compounds – during the 90’s – polyvinyl chloride (PVC) was popular. Today however, it is fairly rare and rather obsolete.

More than 90% of the safety footwear sold and purchased globally will be manufactured out of Polyurethane. Either single density or dual/double density. Dual density has become the global standard due to the fact it offers both a hard-wearing outsole (which takes the impact and pounding of the earth below) and a softer, more cushioned midsole. The midsole, being of a different shore hardness (Shore Hardness is a measure of the resistance a material has to indentation) allows spring and cushioning which provides comfort. Single density doesn’t have this best of both worlds scenario – so has to compromise on either the longevity of a hard wearing outsole or the comfort factor. This ends up either being very hard and inflexible… or not hard wearing enough.

Polyurethane Soles

Polyurethane injected soles in safety footwear; are intrinsically flexible, lightweight, antistatic, oil/acid/petrol & diesel resistant, slip resistant and has a heat resistance of around 90’ degrees to 110’ degrees (on better quality chemicals). Due to the massive quantities sold worldwide, it is the cheapest of the predominantly utilised compounds.

Thermoplastic Polyurethane

Thermoplastic Polyurethane soled product is more specialist; a little less flexible, very lightweight, oil/acid/petrol & diesel resistant, but slightly less slip resistant. It also carries a 90’ degree heat resistant but most importantly, it does have the impressive quality of being cut resistant. A nice feature. Due to its specialist nature – it does carry a price premium.

Rubber Soles

And that brings us to the heavy duty sole offering, which is Rubber. More expensive, heavier, but designed to take on the harshest work environments in construction, engineering and mining. It has a harder compound, offering a superior degree of both cut and puncture resistance, as well as resistance to some harsher chemicals. It also boasts a 300’ degree heat resistant outsole which also makes it non-conductive. Great for applications around both heat, extreme cold and electrical current.

At ProFit Safety Footwear we make use of a range of 5 different anti-static, dual density polyurethane soles – and 4 different heat-resistant and non-conductive rubber soles.

Contact the team today to get advice on the best sole for your purpose – info@profitfootwear.co.za or give us a call on +27 11 892 8030

Polyurethane Injected Soles and Hydrolysis

Our soles are made of PU (Polyurethane soles) in order to be anti-slip, anti-static and oil/acid resistant.

Because PU has organic origins, it is biodegradable over time.

In a society where increasing attention is being focused on protecting our fragile environment, many progressive companies are insisting that, as far as possible, consumables such as safety footwear conform to environmentally sound specifications. The process of biodegradation is slow, taking place over many years, ultimately rendering the polyurethane to a number of benign compounds.

However, to ensure the longevity of the footwear it needs to be stored in the correct conditions. If left in an unventilated area for between 12 and 24 months (or longer), the soles will go through a process called Hydrolysis in which the plasticizer (which makes the soles flexible) leaves the sole, and the soles becomes very soft, then brittle, and begin to crack and break into small pieces.

Hydrolysis is a double decomposition reaction, with water as one of the reactants. Simply put, the oxygen atom in water bonds with the carbon atom of the esters in the polyurethane. This carbon – oxygen bond is unstable, and eventually also breaks down, leading to the gradual disintegration of the polyurethane.

Hydrolysis in safety footwear only becomes a serious issue when four factors combine to create the ideal environment:

  • Water
  • Temperature
  • Darkness
  • Time

Therefore, lengthy storage (longer than two years) in a hot and humid climate is potentially the perfect catalyst for hydrolysis.

New polyurethane formulations and the addition of more sophisticated chemicals significantly retard the process of hydrolysis, but following a few simple steps can almost eliminate it entirely:

  • Rotate stock frequently on a first in, first out basis. Do not keep polyurethane soled footwear on the shelf for longer than a year.
  • Be aware of the climate in which the footwear will be worn.
  • Encourage the wearer to properly aerate the footwear after use.
  • Do not wear polyurethane soled footwear where gumboots would be more suitable.

The effects of Hydrolysis cannot be seen as a fault, but simply a characteristic of the compounds used to create the soles.

However, if warn regularly and the shoes are then in fresh air, warmth and sunlight the product will not experience this process. In fact, the shoes should then last for many years. Boots of 4 to 5 years old are quite commonly seen in good condition when maintained and polished regularly.

We have printed the warning regarding Hydrolysis on the fabric insert inside the box, to make end users aware of it.

Contact the team today to get advice on the perfect fitting safety shoe – info@profitfootwear.co.za or give us a call on +27 11 892 8030