Polymers have
found wide utility in detergent and cleaning formulations for past 25 years and
the largest volume has been simply poly(carboxylates). The word poly-
meaning "many"; and meros meaning "part". A polymer is a large molecule (macromolecule) composed of repeating
structural units (a monomer). Polymerization refers to the process of combining many
small molecules known as monomers into a covalently bonded chain. These
subunits are typically connected by covalent chemical bonds. A heteropolymer
or copolymer is a polymer derived from two (or more) monomeric species,
as opposed to a homopolymer where only one monomer is used. The physical
properties of a polymer are strongly dependent on the size or length of the
polymer chain. Because of the extraordinary range of properties of polymeric
materials, they play an essential and ubiquitous (universal/ global) role in
everyday life. There
are several types of polymers used in detergents and cleaning products. In
general, Examples of polymers used in the detergents and cleaning products
include polycarboxylates, vinyl pyrrolidone and polyvinyl pyrrolidone.
By looking beyond
poly(carboxylates), polymers suppliers are increasing performance options by
several methods. One is to create water soluble polymers with increased
hydrophobicity (aggregate in aqueous solution and exclude water
molecules), which can improve
the soil removing capacity of the polymer by interacting with nonionic
surfactants by various mechanisms. Another is to substitute sulfonic
acid groups for carboxylic acid groups. By adjusting the amount and type of the
sulfonic acid, the polymers show improvements such as increase water hardness
ion tolerance, improved surfactant compatibility, improved film substantivity
and antistatic behavior. A third means is to select a different polymer
backbone, such as a biodegradable polysaccharide or amino acid. By utilizing a
wider selection of reactive functionalities, polymers with improved performance
and multifunctional behavior can be created. Polymeric builders in the form of
anionic polycarboxylates based on acrylic acid account for more than 90% of all
polymers used in detergents. The main function of polymers is of acting as anti-soil
redeposition agent. Apart from this, polymers help in part replacement of
builders like STPP and also inhibit unwanted hydrolysis which results in loss
of active substance.
1.
Soil release benefits: Soil release polymers provide a
barrier to the fabric, which is removed during the wash, together with the
soil. Graft copolymers in laundry detergent compositions can provide soil
release benefits especially of oily soil from cotton fabrics, during the wash. Graft or grafted copolymers contain side chains that have a different composition or
configuration than the main chain. Graft
copolymers providing soil release benefits in laundry detergent compositions
contain backbone units derived from an ethylenically unsaturated monomer,
hydrophilic uncharged side chains, and cationically chargeable or charged side
chains containing a tertiary or quaternary nitrogen atom.
Such
soil release polymers typically comprise an oligomeric or polymeric ester
"backbone". Soil release polymers are generally very effective on
polyester or other synthetic fabrics where the grease, oil or similar
hydrophobic stains spread out and form a attached film and thereby are not
easily removed in an aqueous laundering process.
The
improved release of soil from synthetic fabrics such as polyester has been
successfully achieved, especially with the so-called PET/POET type of polymer,
the effective release of soils, especially oily soils, from cotton has proved
much more difficult.
Function and benefits:
Soil release is a
general term describing the susceptibility of fabrics to the action of cleaning
agents. Soil release agents are materials that modify the fabric surface to
minimize subsequent soiling. Soil release polymers are specific soil release
agents that have been developed, following the introduction of synthetic fibres
into fabrics. Polyester fibre in particular presented a major new soil release
problem, because polyester is a hydrophobic fibre, readily and tenaciously
absorbing oil, making removal of oily stains far more difficult.
Example:
Sorez 100
(polyethylene glycol polyester copolymer) from ISP, Repel-O-Tex SRP-6
(polyethylene glycol polyester) from Rhodia and Texcare SRN 170 from Clariant.
Mechanism:
The mechanism of action for many soil release polymers is that a polymeric
layer is deposited on the fibres and modifies their surface so that subsequent
soiling is deposited on and adheres to the polymeric layer rather than the
fibres themselves. Removal of the soil during the next wash is thus greatly
facilitated. Alternatively some polymers may assist release of soil directly
from the fibres. In
liquid detergents the polymers used to form a layer over remaining soils and
stain particles, lifting them out of the fabrics.
Specific Soil Release Polymers have
been developed to protect the fibres of a polyester containing fabric with a
polymeric film. The presence of this film reduces the affinity of oils and fats
to deposit on the fabric surfaces and makes it easier to remove these stains
during subsequent washing. Soils that are removed during a wash cycle can
redeposit onto the fabric. This undesired effect results in a greying or colour
fading of the textiles. Soil Release Polymers, in particular, several amine
polymers, are used to lift soils from fabrics and keep them in suspension in
the wash water, therefore reducing soil redeposition on synthetic fibres.
2.
Anti-redeposition of soil on
fabrics: Anti-redeposition
agents are detergent
additives used to avoid that dirt redeposits or returns on clothing during the
wash. Anti-redeposition agents are water-soluble and typically
are negatively charged. Carboxymethylcellulose is a polymer derived from
natural cellulose. Unlike cellulose, CMC is highly water-soluble. CMC is used
in some of our laundry detergents at low levels (0.5-1%). It is a dispersion
polymer and helps keeping soil dispersed in the wash water, thereby preventing
it from re-depositing onto the fabrics being laundered. Polyvinyl
pyrrolidone is more
effective with wool and synthetic fabrics. Polyethylene glycol (PEG) and polyvinyl alcohol may also used as anti-redeposition agents.
Role: To prevent soils from resettling
after removal during washing.
Mechanism: Anti-redeposition agents increase
the negative charge on the fabric surface, so that the surface repels soil
particles because these are also negatively charged. Also, polymers prevent the
redeposition of clay sink onto the fabric or hard surface by keeping the
particles suspended in the wash bath. Thus, avoid released dirt to redeposit on
the fabrics during the wash.
Ex. Polycarboxylates,
Hydrophobically modified vinyl pyrrolidone polymers, Carboxy methyl
cellulose (CMC).
a.
CMC
absorbs on to fabric
b.
Polyanions:
For examples, Silicates and phosphates prevent soil re-deposition by stabilizing
the suspended particulate matter.
c.
Polycarboxylates:
Specific group of polyanionic dispersing agents which stabilises the pigments
and perticulates in suspension.
d.
Polyvinylpyrrolidones:
A dye scavenging polymer which absorbs fugitive (quick to disappear) dyes from
wash liquor and prevent re-deposition.
Fig. Example- CMC (carboxy methyl
cellulose) as a antiredeposition agent.
3. Dye
transfer inhibitors:
Help prevent dye from coming off one fabric and getting deposited on other. Dye transfer inhibitor (DTI) are
polymers which are able to entrap the fugitive dyes in the washing liquor. If
a garment loses some of the dye it is coloured with, this will stay in the
washing liquor until it will stick to another garment. This action is called
"colour transfer" and usually happens when garments with different
colours are washed together. DTIs,
usually marketed as "colour care" detergents, are used so that
textiles keep their original colour and whites stay white, even after multiple
washes. In the wash, dye molecules leach (leak/
filter) out of the garments - this is
also called "bleeding" - and the extent to which this happens depends
on newness of the garment, type of fabric, type of dye and washing conditions.
The surfactants in the wash often contribute to this "bleeding"
phenomenon. If such free dye molecules were to redeposit themselves randomly on
other garments, the bright colours would fade. DTI acts as a dye scavenger (searcher/
hunter) preventing dye molecules leaching out of garments from redepositing and
therefore allowing to wash many differently coloured garments together, so they acts as a color protection
agents. PVP K-30, Chromabond S-100 (PVP with betaine functionality) Chromabond
S-400 (PVP with nitrogen oxide functionality) from ISP.
Mechanism
Their function is to bind dyes
which bleed during the washing of colored textiles and so prevent their
redeposition on white or differently colored textiles. DTIs bind irreversibly to free dye molecules in the
wash water and form water-soluble macromolecules. This way, the dyes are
prevented from redepositing onto garments (transfer of dyes from one garment to another in the
wash) and are removed with the spent
wash water.
DTI polymers comprise homo- or
copolymers based on vinylic, nitrogenous, preferably heterocyclic monomers. Not all DTIs work for all dyes. Certain
combinations work better than others, depending on the chemical structures of
the dye and the DTI. The most commonly used DTIs in laundry detergents are
Poly(N-vinylpyrrolidone) (PVP) and Poly(vinylpyridine N-oxide) (PVP-NO). DTIs may be added up to 0.5% (w/w)
to powder specialty detergents for delicate and coloured fabrics.
Ex. Polyvinyl pyrrolidone (PVP), Poly(vinylpyridine N-oxide) (PVP-NO).Both are moderately high molecular
weight polymers very soluble in water.
4.
Work at reduced wash temperature: Polymers have the advantages of
being less temperature sensitive than traditional cleaning ingredients so they
can already function very well at reduced wash temperatures
5.
Sequestration/complexation: Removes calcium ion keeping it in
a dissolved state. Ex. Polycarboxylates
are commonly used in detergents as sequestration/complexation
( Sequestration or chelation (holding hardness minerals in solution)). Ex.
Like builders, polymers acts as sequestration agent.
6.
Dispersion agents (Dispersant): Dispersant cause dispersion of
precipitates in the cleaning bath to avoid setting and scaling on surfaces and
fibres. Also, it causes improvement of filming maintenance by soil dispersion,
which minimizes organic components deposition on glass and dishware’s. The
definition of a dispersing agent is a chemical that is added to oil, cement or
another liquid to prevent it from hardening or clumping. A dispersant or a dispersing agent is either a
non-surface active polymer or a surface-active substance added to a suspension,
usually a colloid, to improve the separation of particles and to prevent
settling or clumping.
Ex. Polycarboxylates
Mechanism: Dispersing agents have an
amphiphilic structure. Dispersing is an act to move and separate an agglomerate
particle to smaller particles. Dispersants break the soil and oil particles in
to small droplets, these droplets disperse (dissolve/ separate) in to the
water. A solid material dispersed in a liquid requires an
additive to make the dispersion process easier and more stable – this is the
role of the dispersing agent, or dispersant.
7. Improve
detergency: Hydrophobically
modified vinyl pyrrolidone polymers which are copolymers having a vinyl
pyrrolidone backbone and pendant (hanging) hydrophobic side chains are useful
in laundry detergent compositions to improve detergency on oily and
clay soils and reduced soil redeposition during the wash (antiredeposition).
Ex.
Diquaternium Ethoxy Sulfate is a polymer used in detergent to lift clay soils
out of fabrics. Polyethyleneimine Ethoxylateis a polymer used in detergent to
lift stains and soils out of the fabrics.
8. Inhibition
of crystal growth:
Prevents precipitation of carbonates phosphates or silicates on fabric.
9. Effective
inorganic cleaning agent / dirt repellent.
10. Modify
the rheology (thickness) of the liquid product: Assist reduce slurry viscosity
prior to spray drying
Polymer effects in detergents:
TYPE
|
MOLECULAR WEIGHT
|
EFFECT
|
Acrylic acid/ maleic acid
|
High
|
·
Encrustation inhibitor
·
Reduction of slurry viscosity
·
Antiredeposition agent
|
Acrylic acid/ maleic acid
|
Low
|
·
Reduction of slurry viscosity
·
Dispersing agent
|
Acrylic acid
|
High
|
·
Dispersing agent
|
Acrylic acid
|
Low
|
·
Antiredeposition agent
·
Dispersing agent
|
Graft polymers on polyalkylene
glycol
|
·
Antiredeposition agent
| |
Polyvinylpyrrolidone
|
·
Dye transfer inhibitor (DTI)
| |
Amphiphilic tetraphthalic acid
polyester
|
·
Soil release agent
|
Physicochemical properties of
polycarboxylates
Polymer type
|
Chemical form
|
Molecular weight
|
Viscosity (mPa.s)
|
CCDC (mg CaCo3/g)
|
Acrylic acid/ maleic acid
|
Sodium salt
|
70000
|
2800
|
290
|
Acrylic acid/ maleic acid
|
Low
|
3000
|
100
|
310
|
Acrylic acid
|
High
|
100000
|
1000
|
120
|
Acrylic acid
|
Low
|
8000
|
1000
|
125
|
CCDC= CaCo3 dispersing capacity at
23OC, 1% polymer solution, pH 11