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Polyurethanes – What Goes Into PUs?

  • —A PU is made by mixing together the ingredient chemicals (Isocyanate and Polyol) in predetermined proportions, which then react to form the polymer PU.
  • —Uniquely, PUs utilise simultaneous polymerisation and shaping of the part.
  • —The production of consistent end products depends on mixing, in precise ratio, the ingredient chemicals and maintenance of the appropriate processing temperatures. As the liquid Isocyanate and Polyol react to form the PU, the liquid mix becomes increasingly viscous eventually forming a solid mass. The reaction is exothermic and therefore heat is involved.
  • —Other ingredients will be included in the polyol blend, for example the catalyst which controls the rate at which the liquid mixture reacts to become solid.

Success is due to well chosen technology

There are no hard and fast rules for obtaining the optimum PU end product, success is due to good formulation selection with well chosen and appropriate processing parameters, technology and mould geometry. The process by which liquid polymers are converted to elastomeric or glassy solids is fundamental to the manufacture of PU products.

Selection of a Polyurethane

  1. —Consider the requirements which the application will demand of the PU with respect to chemical and physical properties.
  2. —Based upon an understanding of what controls these properties select a few candidate PU systems.
  3. —The properties of a PU are largely controlled by the chemical nature of the system and how it is processed so it is prudent to consult specialist suppliers and processors at this stage.

Basic Polyurethane Chemistry

  • —The simplest PU is linear in which the hydroxyl compound and the nitrogen compound each have a functionality of two. This can be represented by the following:

Isocyanate + Polyol = Polyurethane

  • —The isocyanate can react with different chemical groups, so the final properties of the polymer will vary according to the reaction route taken.
  • —Therefore the formulation of a PU must take into account every possible reactive constituent. PUs may have a very widely varying structure depending on the type of isocyanate and the type of reactive hydrogen components present in the formulation.
  • The presence or otherwise of the various groups along the urethane linkage will control the end properties of the polymer.
  • The curing of a PU can be regarded as the formation of a network, also called cross-linking, the extent or degree of cure is often expressed as the crosslink density.
  • The extent of cross linking may vary and will be reflected in the final properties of the PU, ranging from longer, linear chains of flexible elastomers and foams to the rigid, heavily cross linked polymers.

Chemical Structures

isocyanates

polyols

Posted by:
Prem Mehani 
for Pinza Footwear
Email. pmehani@yahoo.com

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Footwear tips for Monsoon

Monsoon, the rainy season, in India is like a festival. After severe heat people are waiting for the rain and when it comes, people can be seen dancing in rain and rejoicing in many ways.

A pleasant weather is not the only thing that monsoon brings for us. It is well equipped with not only the higher chances of fungal and bacterial infections, but also the chances of slipping on wet surfaces.

Last week after a day’s rain in Mumbai my daughter slipped on water covered stairs causing bruises and grounded her for a day. She missed her Mumbai Darshan organised by NMIMS, Mumbai for freshers of the college.

Following on, I thought I’d write about footwear you can use for the coming rain season.

Mentioned below are few tips that will help you in buying right footwear for monsoon and keeping your feet happy and infection free this season.

Flip-Flops made of rubber or materials from PVC are ideal for the rains, because they are washable, dry easily and easy-to-maintain footwear. They are available in a range of designs and colours and are suitable for both girls and guys.

Full Plastic Footwear are low-cost options for rainy season and are widely used in heavy rains. Nowadays they are available in varied style generally looking like stylish leather shoes.

Crocs are a better option for the rains. They are essentially rubber, and their grip is also better, so they won’t slip from your foot when both are wet with rain water. Colourful options with holes on top make them a style statement for monsoon.

With a formal outfit, you can wear sandals with straps as they would be firm on your feet. Go for slip-resistant sandals and check that your wet feet don’t slip even inside the footwear.

Open toes or closed shoes: Open toes or peep toes are available in waterproof material from PVC. They come in colours like red, pink, blue, silver and gold. Flat Ballerinas or closed shoes made from Lycra look great and survive monsoon.

Gum Boots: There is nothing better than rain boots and Gum Boots to protect your feet in heavy rains. This waterproof footwear is usually knee-high, water-proof and are mostly made from rubber or PVC. These boots protect the feet from mud, dirt and water during monsoon.

Avoid

  • Avoid wearing heels in rainy season. But, if you just cannot resist wearing heels then go for slip-resistant sandals of heels not over 2 inches.
  • Avoid wearing leather footwear as much as possible since the material gets easily infected with fungus and bacteria. They have a tendency to support bacteria because of the moisture.Still have passion for leather footwear, look out for Waterproof shoes. The waterproof range of well-known brands is quite stylish and perfect for a rainy day. Formal shoes made of waterproof leather and shoes with foam base that are odor-resistant are a huge hit with office-goers.

Here are some tips while purchasing your footwear for monsoon:

  • While purchasing plastic footwear, make sure that the pair doesn’t have any sharp edges as those could give you shoe bites.
  • For this season particularly, whether you are buying flat sandals or heels, look for footwear with good grip that hold feet in place and do not slip when the feet and shoes are wet.

Don’t

  • During monsoon do not wear sports or canvas shoes as they may attract the growth of bacteria.
  • Don’t keep your shoes and sandals under the bed or inside the shoe rack when it is wet. This gives birth to bacteria’s. Let them dry under the sun to keep away the bacteria’s from breeding in your shoes.

Mentioned below are few tips that will help you keep your feet infection free in Monsoon.

  • Camphor powder is an effective antiseptic. Mix it with talcum powder and apply before wearing shoes and after opening them.
  • Rubbing onion juice between infected toes helps to cure infection faster.
  • If you develop itch due to mud water, wash feet in a mild solution of lime juice and vinegar to reduce the itch.
  • If your wet feet have tendency to cause odour, mix 5 ml of peppermint oil in a tub of lukewarm water with handful of neem leaves and soak your feet for 10 minutes. Dry and spray talcum powder on it. This will help in reducing the perspiration plus relieve you from odour-causing bacteria.
  • Sometimes in this season our nails become soft, brittle and start to clip. You can prevent this by adding a few drops of olive oil and lemon juice to a tablespoon of honey and apply this mixture to the nails before sleeping to treat brittle nails.
  • At the end of a humid rainy day, soak your feet in cold water and salt solution. Scrub, clean and wipe dry.
 
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Posted by on June 24, 2012 in Buying Footwear

 

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