Friday, August 21, 2009

Who are P2i? P2i was founded in 2004 as a commercial spin-out of the Defence Science and Technology Laboratory; the centre of scientific excellence fo

Applied to Performance
Textiles (Footwear)


Introduction.

The global footwear market is huge with a market value
estimated to be $200 billion pa. The US market for athletic
footwear (of which performance footwear is only a part) is valued
at $10 billion pa, of which around $3 billion is running shoes.
The European market (dominated by the UK, Germany, Italy,
France and Spain) accounts for around €7.5 billion pa

Many different materials are used when manufacturing
shoes from polymers to natural and synthetic fibres, leather,
suede, plastics and metals – all of which perform differently
in different environments. The materials themselves can
be of little relevance as the performance of the product
relies heavily on how the materials are combined and how
the product is constructed. Although the performance of
the materials is often quoted, the performance of the end
product can often be very different.
Whilst most naturally occurring fibres are inherently
hydrophilic, certain materials can display a degree of
hydrophobicity due to oils naturally present in the material
e.g. leathers. Synthetic fibres are often wetted by water and
so the fully constructed product may display a variety of
responses to the interaction with water.

For footwear, protection from the elements usually translates
in to the ability to resist water.

The degree of resistance required will vary depending on the
application and environment associated with the intended
use. Despite these initial thoughts, when the product is
worn other observations become apparent:

• Performance of the materials is very different from the
performance of the footwear due to mechanism of use,
construction criteria and methodology e.g. material
selection and size / position of seams.

• While the shoe needs to protect the wearer from water
outside the shoe (rain, puddles, wet grass etc), the
heat and sweat generated inside the shoe also need to
escape. Translated, there is a need to not only protect the
wearer from the external threat but also the internal threat;
if not, the wearer will suffer from ‘over-protection’.
• As the level of protection is increased e.g. from a sandal
to a fully water-proof Wellington boot, the heat burden
increases. This is due to an unavoidable compromise; the
greater the protection, the greater the heat burden and
vice versa.

• Whether the footwear in question is absorbing water from
the outside elements or the internal microclimate, the
shoe will increase in weight and therefore increase the
energy expenditure during movement.

• Materials which permit air to flow through them will
generally feel more comfortable than those that prevent
air-flow (for all but extreme conditions) due to the benefits
of enhanced evaporative cooling (although sometimes
wind-proofness is a desired effect).

It is therefore clear that a revolutionary technology for the
footwear industry would need to be applied to the fully
constructed shoe so all materials are adequately modified.
It would also need to display high levels of liquid resistance,
without changing the desired air-flows of the product and so
minimising the heat burden.

The patented ion-mask™ nano-coating from P2i Ltd
(WO 98/58117) has been commercialised to provide cost
effective turn-key processing facilities to carry out plasma
enhancement of footwear to produce high water resistance
that retains the desired levels of air-flow, by preventing
‘over-protection’.

Numerous benefits can now be realised using this simple
approach, allowing all footwear products to be enhanced
cost effectively using the highly environmentally-friendly
process of plasma enhancement and conferring design
bespoke benefits.

Introduction

The global footwear market is huge with a market value
estimated to be $200 billion pa. The US market for athletic
footwear (of which performance footwear is only a part) is valued
at $10 billion pa, of which around $3 billion is running shoes.
The European market (dominated by the UK, Germany, Italy,
France and Spain) accounts for around €7.5 billion pa.

Technical Background.


Many chosen materials, in products all around us, are selected
for either their bulk physical properties or ease of processing.
However, their resulting surface properties can be far from ideal
for their intended use. Plasma processing allows the surface
properties, typically nanometres in thickness, to be optimised
without affecting the bulk properties and allowing the product
to perform at a much higher level in its intended application and
often opening up new applications altogether.

Plasma processing is a widely accepted technique
for altering the surface properties of complex objects,
regardless of composition, without altering the bulk
properties. Chemical tailoring of the solid surface through
retention of starting chemical functional groups can be
obtained by modulation of the plasma power. Constructed
items with complex shapes or deep orifices can be
easily treated due to the penetrative nature of the
plasma process and its non-discrimination between
different materials.


Introduction to plasma processing.


Carrying out reactions in the gas phase is highly desirable
as the reactive species have a high level of mobility and
a greater chance of reacting. Plasma chemistry is the
production of an ionised gas and over the last 30 years
has become popular for surface modification and the
deposition of polymer films.

A plasma (or electrical discharge) is a partially ionised gas,
often referred to as the fourth state of matter - the other
three states being solid, liquid and gas - and changes
between them are possible through a change in energy.
The term plasma was first used by Langmuir in 1929 to
describe the state which makes up the vast majority of
the known universe, mainly in the form of stars. A plasma
consists of many reactive media including electrons,
positive and negative ions, radicals, neutrals, metastables
and electromagnetic radiation, all of which are capable of
participating in or initiating reactions. In order to be termed
a plasma, there must be an equal number of positive and
negative species present, although local perturbations
from neutrality occur, the overall charge must be neutral.

The type of plasma concerned with here are low
temperature, non-equilibrium plasmas, meaning that
the electrons, ions, neutrals and radiation are all at
different temperatures.

The hottest part of the plasma are the electrons, but due
to their tiny mass these do not heat up the items being
processed significantly and can indeed be modulated to
give only very small increases in temperature. These types
of plasma are termed glow discharges and are used to
carry out non-thermally activated reactions.

The glow discharge is initiated by passing radio frequency
around or through a low-pressure gas or vapour. This
creates a number of reactive molecules, some of which
can alter the material surface or polymerise to form an
ultra-thin polymer film. By choosing the required power,
and carefully selecting the starting chemical, surface
functional groups can be grafted to the material to give rise
to a wide range of properties offering numerous additional
benefits to the unprocessed material or product.
Due to the gaseous phase processing and relatively
low degree of ionisation, neutral molecules will readily
permeate what appears to the eye as a complex 3D
structure. By careful control of other plasma parameters
such as pressure flow rate and power, the plasma can
access all nooks and crannies with ease and build up the
desired effect through molecular bonding to the product.

Focus on Footwear


Conventionally, when trying to render footwear highly water
resistant, one of three approaches is taken:

• Use inherently highly water resistant material, eliminate
stitching and form as a single section. The most
common example of this is a Wellington boot.

• Apply durable water repellents (DWR) to the fabric used
in the shoe construction or as a wash-in treatment for
the footwear.

• Redesign the shoe to minimise stitching and permeable
materials and include a highly water resistant material
in the form of a physical barrier to water penetration
(usually in the form of a continuous film or membrane).
It is also likely that a DWR will be used on the outer
material to provide a degree of liquid repellence.
Although all these techniques are perfectly adequate
for niche applications, none of them provides a suitable
process across the full product range.

The first description in this list describes a Wellington boot
which is commonly accepted as ‘waterproof’ since there
is no physical way for water to pass through the boot as
the material is impermeable to water (other than at a force
equivalent to its burst strength) and there are no holes in
the boot, except for where the foot enters.
Common materials used in footwear manufacture are
inherently water wetting and so DWRs are applied to increase
the level of resistance. The DWRs are applied to the fabric in
roll format where a complex chemical formulation is pad dry
cured to the fabric at around 160°C.

This formulation is generally specific to the chemical nature
of the material it is being applied to. On completion, the
desired shapes for shoe construction will be punched out and
stitched into the upper before being lasted onto the insole.
It appears that few DWRs actually display an adequate level
of protection under dynamic testing, Figure 1.

Focus on Footwear.

The ion-mask™ enhanced shoe fabric displays high levels of resistance to water ingress under flexing and even after
100,000 flexes, no water penetration has occurred.

Contrary, the untreated shoe fabric and the DWR fabric
for shoes show water penetration almost immediately. In
addition it is important that the water resistance effect can
be maintained following mechanical abrasion.
Figure 2 displays the high level of water repellency shown
by ion-mask™ enhancement, carried out by spray rating
test, following a number of abrasive rubs.

For Further Information please visit website:-
http://www.p2ilabs.com/images/stories/P2iTechnicalPapers/footwear%20and%20textile%20tech%20paper%206695-0808.pdf

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