Features

Polymeric Delivery Systems for a Sustainable Planet

By Robert Y. Lochhead, Vipul Padman and Lauren LaBeaud, The University of Southern Mississippi | April 2, 2012

Marketers and suppliers patent skin care polymers that are better for consumers and reduce the carbon footprint of products.

Patent searches during the past several months have revealed a trend toward polymeric delivery systems for consumer goods that lead to less waste going to landfills and lower carbon footprints. There has also been a thrust toward using polymers to provide perceptually safer products to the consumer by this industry, which already has an excellent record of consumer safety. This article is devoted to these two megatrends.

The consumer goods sector is driving hard toward providing the products and logistics for a sustainable planet. For example, Kurt Bock, chairman, BASF, stated, “For us, sustainability means aligning economic success with environmental and social responsibility and BASF has openly presented its carbon footprint since 2008.”1 In 2010 Procter & Gamble launched a long-term sustainability vision that included the goals of “having zero consumer or manufacturing waste going to landfills” and “designing products that delight consumers while maximizing the conservation of resources.”2

Unilever has launched a sustainable living plan with the stated goal, “By 2020, we will halve the environmental footprint of our products, help more than one billion people take action to improve their health and well-being, and source 100% of our agricultural raw materials sustainably.”3

SC Johnson pronounced “our sustainability efforts target five key areas. From greener products, to conserving resources, to helping communities, these are the areas where we believe we can make the greatest impact;” meanwhile, Estée Lauder’s Aveda was founded on a drive to ecologically sustainable products.

Reducing Water
One initiative in this direction is to reduce the volume and the water content of products or precursors in order to reduce the carbon number associated with distribution of the product. Emulsions are a preferred mode of delivery for many skin products and the reduction of water content of emulsion would fit right into a sustainability objective. Cognis researchers have disclosed one such emulsion concentrate.4 They combine the water insoluble components (including oils) with nonionic emulsifiers, co-emulsifiers, polyols and water. The stability of the emulsions is optimized by Shinoda’s technique of preparing the emulsion above the phase inversion temperature and then cooling below this temperature to prepare the final emulsion with exceptionally small droplet sizes. In one mode these emulsions are applied to nonwoven substrates to make wipes for application to skin.

But what if the nonwoven could be the product? There would be virtually no waste going to landfills. This is possible, based on a P&G patent for nonwoven filaments that contain active ingredients to deliver materials to skin, hair, dishes, laundry and the like.5 One set of products that could be directed toward these goals is made of fibrous webs of dissolvable fibers that can be quickly and easily dissolvable in the consumer’s hand.6 Moreover, fibers are made of a surfactant, a structuring polymer, plasticizer, an extensional rheology modifier and other additives that confer the desired attributes of the finished article that could eliminate the water from a formulation and printing thereon could radically reduce the amount of packaging material.

In the Glenn et al. patent application, the surfactants are classified into foaming and non-foaming types. Formulators would recognize the foaming type to be similar to shampoos and cleansers, and the non-foaming type to be more like conditioners. The structuring polymer is a water-soluble polymer such as poly(vinyl alcohol), poly(acrylate), PVP, PEO, starch, pullulan or cellulose ethers. The extensional rheology modifiers enable the formation of thin fibers rather than a spray of droplets when the fiber is spun because liquid jets tend to break up into droplets as a result of Plateau-Rayleigh Instability. For the production of sprays, one seeks conditions that favor Plateau-Rayleigh instability, but for the production of fine fibers it is important to try to avoid such instability. Plateau-Rayleigh instability results from perturbations that are always present in a thin liquid tube. Some of the perturbations can grow until they pinch the fiber into drops. The thinner the liquid tube, the more likely it is to be unstable. This is usually demonstrated by controlling the flow of water from a faucet. As the tap is slowly turned down, the liquid stream flowing from the faucet becomes progressively thinner and eventually breaks into drops. If a liquid is viscous or it contains an associating solute or an entangled polymer solution, then the liquid can be spun into much finer filaments, due to the increase in extensional viscosity of the system. Thus the extensional rheology modifiers are required to enable spinning of extremely fine fibers. This is especially important in this case because the dissolution time in the palm of the hand will be faster as the dissolvable fibers in the product become ever finer. Extensional rheology modifiers are usually high molecular weight soluble polymers. In this case it seems that high molecular weight poly(ethylene oxide) is preferred. Very fine fibers can be made via spunbonding, electrospinning, meltblowing or melt fibrillation.

This patent particularly emphasizes spunbond and fibrillation. Spunbond fibers are produced by extruding a “melt” through a series of fine capillaries and the filaments are progressively reduced in diameter. Melt film fibrillation was developed Torobin and by Dale Reneker’s group at the University of Akron and it involves the formation of a small concentric film by extrusion through an annulus. Simultaneously, high velocity air is forced through the annulus and as the film emerges, the air causes it to fibrillate into many small diameter fibers. The fibers are then formed into a nonwoven mat on a conveyor or on a drum.


Figure 1: SEM of melt-fibrillated surfactant-containing fibers. Reproduced from US Patent Application 200120021026.

Figure 2: SEM of spunbond surfactant-containing fibers. Reproduced from US Patent Application 200120021026.
Figure 1 is a scanning electron micrograph, from the patent application, of the melt fibrillation surfactant containing fibers and Figure 2 is a scanning electron micrograph of spunbond surfactant containing fibers. The fibers dissolve quickly when exposed to water and this is demonstrated by the series of micrographs in Figure 3 that show the dissolution process. Examples of this technology include shampoos/body washes prepared from either a spunbond process or a fluid fibrillation process. The formulation ingredients for these two examples are shown in Tables 1 and 2, respectively. With this technology, it is possible to homogeneously mix different fibers or filaments within a single nonwoven mat. Thus, multifunctional products are possible in which one fiber functions initially in the process and another fiber functions separately in a next stage such as a shampoo and conditioner in one product.
















Figure 3: Dissolution of a surfactant-containing fiber in water. Reproduced from US Patent Application 200120021026.




















Table 1: Formulation ingredients for the preparation of surfactant-containing fibers by a spunbond process (US Patent App: 200120021026).

Ingredients: %Wt.
Glycerin 3.2
Polyvinyl alcohol 8.1
Sodium lauroamphoacetate (26% activity) 1.8
Ammonium laureth-3 sulfate (25% activity) 4.9
Ammonium undecyl sulfate (24% activity) 19.9
Ammonium laureth-1 sulfate (70% activity) 8.0
Cationic cellulose 0.5
Citric acid 1.6
Distilled water 22.0


pH: 5.8; Viscosity (cp): 35,400


Table 2: Formulation ingredients for the preparation of a soil dissolvable shampoo by a fluid fibrillation process (US Patent App: 200120021026).

Ingredients: %Wt.
Glycerin 13.5
Polyvinyl alcohol 8.1
Sodium lauroamphoacetate (26% activity) 38.2
Ammonium laureth-3 sulfate (70% activity) 2.9
Ammonium undecyl sulfate (70% activity) 9.8
Ammonium laureth-1 sulfate (70% activity) 9.8
Cationic cellulose 0.5
Citric acid 2.3
Poly(ethylene oxide) 2.0
Distilled water 2.0

pH: 5.8; Viscosity (cp): 35,400

Films
Films formed by combining a water-soluble polymer with a water insoluble polymer can be used as controlled release delivery systems for therapeutics, fragrances, flavorings, colorants or other cosmetic materials.7 The polymers and the functional active agents are prepared in the form of a slurry which is cast into a film. Preferably, the film is cut into pieces such as flakes and the flakes are then incorporated into a liquid vehicle to make the final product. For skin care applications, the functional materials can be surfactants, sunscreens, conditioners, moisturizers, antioxidants, enzymes, antibacterial agents, occlusive agents, exfoliants, lighteners and anti-aging ingredients. In an example of a body wash, the film is formed by mixing PVP and PVP/VA copolymer, a dispersion of poly (ethyl methacrylate) in ethanol and a functional ingredient in ethanol. A film was cast from the resulting polymer solution/slurry and the film was cut into flakes, which were suspended in a body wash formulation that contained sufficient acrylates copolymer to suspend the flakes.

Polymeric Antimicrobials
One aspect of sustainability is mitigating or eradicating the presence of harmful or perceived harmful ingredients. One subject of such perceived concern is the use of antimicrobial ingredients. There is an apparent dilemma here—because antimicrobials must be active biocides against living microorganisms but should not be harmful to humans, animals or plants. It has been argued that polymeric antimicrobials could be designed to be effective against a broad spectrum of harmful microorganism, but the polymeric agent itself would be too big to penetrate the skin and this would add an element of safety to the use of broad-spectrum antibacterials.

A geographically diverse group of researchers have approached this challenge by substituting polyethylenimine with alkaryl groups.8 The expectation is that, in addition to being less able to penetrate the skin, these materials would be more substantive to skin which would provide antimicrobial protection for a longer duration and reduce the amount of these compounds that would be released to the environment. Moreover, functionalization with other functional groups could allow the solubility of the antimicrobial agent to be designed and incorporation of several antimicrobial groups into one polymeric molecule could allow the formulation of “broad-spectrum antimicrobial cocktails” without the worry of the incompatibilities that are encountered when one tries to add more than one antimicrobial compound to a formulation. The polymeric antimicrobial approach is interesting and it is one to be watched as it emerges to, hopefully, make our products even safer than the present exceptionally high level of safety.

In an interesting application, University of Florida researchers have pointed to silanols as antibacterial agents.9 The silanols are identified as trialkylsilanols, siloxanediols and siloxanols. These all contain OH groups attached to a Si atom. It is well known that such a bond is unstable with respect to condensation, which converts it to an Si-O-Si group. The latter group is the backbone of silicones, and this reaction is used to prepare silicones and also to drive sol-gel reactions. One way that the researchers overcome this inherent instability is to attach the silanols to polymers that contain hydroxyl groups to “silylated” polymers that release the silanols by hydrolysis in situ when the silylated polymer is applied to the appropriate substrate, such as topical application to the skin surface. The silylated polymers include polysaccharides, proteins, poly(alkylene glycol(s)), and amine and hydroxyl terminated polymers. It is also interesting that one embodiment is described in which the silanol is attached to filaments of, for example, cotton especially for use as dental floss.

In our previous article (Happi, April, 2011, p. 72), we reported that J&J researchers had correlated the effect of polymers to increase the critical micelle concentration of a surfactant or surfactant mixture was correlated to a reduction in skin irritation. Three more patent applications have now been published that extend the technology to non-crosslinked linear acrylic polymers in relatively low non-ethoxylated anionic surfactant(s), and also for high-clarity, high-foaming cleansers with relatively low surfactant concentrations. 10

Safer Skin Penetration
Kosmotropes were originally defined as substances that enhanced the order of proteins and biological membranes. Chaotropes do exactly the opposite; that is, they disrupt the order of proteins and membranes. Unilever researchers have identified chaotropes as agents to fill the need to enhance the delivery of therapeutic agents to and through the skin without irritation or unpleasant symptoms.11
There is also a need for transdermal delivery of actives in a safe, affordable convenient and environmentally-friendly manner. The preferred chaotrope in this instance is guanidinium chloride, which is claimed to enhance the delivery of agents for skin-lightening, moisturizing, deodorizing, antiperspirancy, acne treatment, wrinkle reduction and especially for self-tanning. The preferred self-tanning agent is dihydroxyacetone. The compositions are exemplified by the formulation here:


Ingredients: %Wt.
Water q.s.
Glycerin 4
Silicone emulsifier (Cyclopentasiloxane
(and) PEG/PPG-18/18 dimethicone)
3
Cross-linked and alkyl-modified
dimethicone blend (Dimethicone/vinyl
dimethicone crosspolymer
(and) cyclopentasiloxane)
1.5
Silicone fluid (Cyclopentasiloxane) 8
Elastomer blend (Cyclomethicone
(and) dimethicone crosspolymer)
5
Dimethicone fluid 1.5
Polyethylene microspheres 4
Guanidinium chloride 2.5
Dihydroxyacetone 2.5

Sourcing from Nature
DuPont has moved toward naturally-derived products by disclosing micronized polyester beads that are synthesized using plant-derived diols. The beads exfoliate skin with the perceived advantage that they are naturally-derived rather than petrochemically-sourced and are less coarse and irritating to skin than the natural kernel powders, that are stated to cause micro-cuts on the skin surface.

We can see the beginning of innovations that will transform the skin products that are offered to the consumer. The trend toward sustainable sourcing of raw materials is being reinforced by the design of new products that produce less waste, lower our carbon footprint, use less water and are more pleasing, lower irritating and offer safety that is perceptible to the consumer. This is an exciting time and these developments could transform our industry.

References
  1. http://www.basf.com/group/sustainability_en/index
  2. http://www.pg.com/en_US/sustainability/environmental_sustainability/index.shtm.
  3. http://www.unilever.com/sustainability/
  4. G. Strauss, R. Kawa, P. Schultz, A. Stork, Emulsion concentrate, U.S. Patent Application 2011/0287073, Nov. 24, 2011, assigned to Cognis IP Management GmbH.
  5. R. W. Glenn, Jr, G.C Gordon, M.R. Sivik, M.R. Richards, S. W. Heinzman, M.D. James, G. W. Reynolds, P. D. Trokham, P. T. Weisman, A. H. Hamad-Erahimpour, F. W. Denome, S . J. Hodson, Filaments comprising an active agent nonwoven webs and methods for making same, U.S. Patent Applications 2012/0027838, Feb. 2, 2012; 2012/0048769, Mar. 1, 2012; 2012/0052036, Mar. 1, 2012; 2012/0052037, Mar. 1, 2012; 2012/0058166, Mar8, 2012.
  6. R. W. Glenn, Jr, R. Chhabra, W.M. Allen,Jr, J. P. Brennan; Jonathan Paul, Dissolvable Fibrous Web Structure Article Comprising Active Agents, U.S. Patent Application 2012/0021026, 20012/Jan. 26, 2012.
  7. S. Ibrahim, M. Omer, K. L. Wisnieski, D. Salko, A. Haskel, K. Connor, Film containing compositions, U.S. Patent Application 2011/0293539, (Dec 1, 2011), assigned to the Colgate-Palmolive Company.
  8. X. Huang, T. Diesenroth, A. Preuss, S. Marquais-Bienewald, C. Hendricks-Guy, J. Jennings, Polymeric antimicrobial agents, U.S. Patent Application 20110318280, Dec. 29, 2011.
  9. L. Jin, R. H. Baney, Antimicrobial compositions, methods of manufacture thereof and articles comprising the same. U.S. Patent Application 2011/0287074, Nov. 24, 2011, assigned to the University of Florida Research Foundation Inc.
  10. R. M. Walters, E. T. Gunn, L. Gandolfi, D. Johnson, E. Anim-Danso, K. Lahey, Low-irritating, clear cleansing compositions with relatively low pH. U.S. Patent Applications 2011/0319306, and 2011/0319307, 2011/0319308, Dec. 29, 2011.
  11. A. Lou, Q, Qiu, Topical composition containing a chaotrope, U.S. Patent Application 2011/0286942, November 24, 2011.

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