Application of Polymers in Detergents:

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.

Role of polymers:

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.

                          Fig. Mechanisms in the dispersion process

 

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 23^OC, 1% polymer solution, pH 11