Natural based adhesives

The elastomers considered in this section have been selected considering the most commonly used in rubber base adhesives natural rubber butyl nibber and polyisobutylenes styrene-butadiene rubber nitrile rubber polychloroprene rubber (neoprene). Typical properties of these rubbers are shown in Table 2. 

Pressure-sensitive adhesives (PSAs) based on acrylic, natural rubber and silicone are employed primarily for ease of application. To name Just a few applications, PSAs bond decals to surfaces, interior decorative surfaces to interior panels, interior trim pieces in place directly or hook and loop tape for the same purpose, structural shims in place during manufacturing and acoustic (sound deadening) materials to body skin interior surfaces. Tape products with pressure-sensitive adhesive on one or both surfaces are used for such functions as cargo compartment sealing, as a fluid barrier to prevent spills and leaks in the lavatories and... 

Contact adhesives. Natural and synthetic rubber-based contact adhesives are used for bonding various interior decorative materials such as fabrics and decorative laminates to underlying surfaces. 

Natural-product-based structural adhesives include protein-based adhesives, starch-based adhesives, and cellulosics. 

The development of useful adhesive compositions based on the interaction of isocyanate resins with natural polymers such as lignin, proteins, and carbohydrates. 

Another, and perhaps the most important, obstacle to increased use of adhesive polymers based on natural products relates to our inadequate knowlege of the fundamental chemistry of these systems. A large body of empirical formulation work is generally required in the development of new adhesives, and success often rests on how well that work is done. However, knowledge of the structures and reactions of these polymers is just as important and usually re-... 

Several mechanisms of interaction between particles of solids are known [3]. Mechanical adhesion is achieved by flowing a metal into the support pores. The molecular mechanism of adhesion is based on the Van der Waals forces or hydrogen bonds, and the chemical mechanism on the chemical interaction of the metal particles with the support. The electric theory relates adhesion to the formation of an electric double layer (EDL) at the adhesive-substrate interface. Finally, the diffusion mechanism implies interpenetration of the molecules and atoms of the interacting phases, which results in the interface blurring. These insights into the nature of adhesion can be revealed in the papers about the interaction of transition metal... 

Examples of biomaterials include sodium hyaluronate, a naturally occurring biopol3nner used to reduce the incidence of postsurgical adhesions polymer-based materials for controlled-drug release and tissue engineered scaffolds to... 

Natural adhesives are based on products some of which are taken from the food market... 

To enhance cell adhesion PEG-based (Hem and Hubbell 1998 Burdick and Anseth 2002 Burdick et al. 2004) and other hydrogels have been modified with amino acid sequences derived from natural proteins, e.g. integrin-binding domains as RGDl... 

The adhesion of a paint to the substrate is a presupposition for the performance of the coating as a corrosion protecting layer. Adhesion is based on the physical and chemical behavior of the underside of the paint and the surface of the metal substrate. The formed interfacial zone should be called an interphase rather than a sharp interface because it is three dimensional in nature. 

In addition, it must not lose adhesion as a result of perspiration, but must permit easy and clean removal. Traditional adhesives were based on natural rubber and zinc oxide, but water-based acrylic systems now dominate. 

As a consequence of the outstanding properties of polyurethane as a porous material and therefore for synthesis of membranes, research continues focused not only on environmental fields but also in diverse areas such as medical devices or adhesives. Therefore, there is a potential area to develop polyurethane-separation materials as membranes. The use of naturally based polyurethane monomers during synthesis reactions [polyol, isocyanates, and chain extenders), are also key factors to explore in future to control morphological, mechanical, and thermal desirable properties. In addition the modification of polyurethane with potential natural absorbent biopolymers is an emergent research line that has demonstrated successful results [9,81,82]. 

Figure 11.1 Total worldwide production of adhesive and sealants including share of natural-based components.

Quality Features and Gaps with Natural-based Adhesives and Sealants... 

Adhesives and sealants based on renewable sources show a number of advantages, but also major disadvantages that effectively limit their broader use at present. On the positive side they usually show an excellent bio-compatibility given that their chemical modification did not completely alter this. Natural-based products in general show a positive Greenhouse Gas (GHG) balance, and thus do not directly contribute to climate change. They show a fairly good price/performance ratio, usually are available in sufficient quantity and show no or low toxicity. 

However, natural-based materials like starches and soybean oils are used in direct competition to animal or human food consumption. Technically, they are not at all suitable for high modulus adhesive and sealant joints. They usually are sensitive to hydrolysis and oxidization. Exposure to atmospherie eonditions or chemical attack can drastically limit their service life expectancy. They are sensitive to elevated temperatures and need to be protected against microbiological decay with more or less toxic preservatives. In light of those features and based on today s knowledge some important conclusions can be drawn ... 

Sustainable Solutions for Adhesives and Sealants 433 Table 11.1 Typical quality features when using natural-based components in adhesives, foams and sealants. ... 

T able 11.2 Global status for use of natural-based adhesives (wet mto, average solids 50%). 

Total wet adhesives natural and petrochemical based Total share of natural-based adhesives 14120 15.50% 16608 15% 4.1... 

Table 11.2 gives a survey about major use areas for adhesives based on renewable sources. The share of renewable raw materials in the sealants market is well below 5%. Numbers in Table 11.2 do not include polyurethanes containing oleochemical-based polyols, vegetable oil-based polyesters and polyamides based on dimer fatty acids in total estimated at 35 mto in 2006, 42 mto in 2010. Projection into 2010 shows that without disruptive innovations the share of natural-based adhesives will further decline to a mere 15% in total. 

Uses Intemiediate for acrylic latexes and S/B latexes for paper coatings, carpetbackings, nonwoven textiles, adhesives, and paints reactive comonomer for acrylic, S/B, PVAc, nitrile latexes prep, of acrylic fibers copolymerization of nylon (caprolactam base), resins, plasticizers, interm iates, paper additives aluminum anodizing reagent lube oil additive in food-contact paper/paperboard in food-pkg. adhesives natural food acid (Japan) in cellophane for food pkg. 

The need to substitute synthetic thermosetting wood adhesives with more environmentally acceptable resins has led to intense research on adhesives derived from natural, non-toxic materials. Extensive reviews on the subject exist [4,5]. It is sufficient here to state that lignin is one of the materials at the forefront of these studies. Numerous wood adhesive fomulations based on lignin have been published over the years [6]. 

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