Pressure-sensitive adhesive chemistry

The section on chemistry of adhesives evolves from rubber-based adhesives to semi- structural and finally to structural adhesives. Everaerts and Clemens provide a thorough description of chemistry and applications of pressure sensitive adhesives and Kinning and Schneider describe an enabling technology for pressure... 

Kinning, D. J. Schneider, H. M. Release Coatings for Pressure Sensitive Adhesives. In Surfaces, Chemistry Applications, Chaudhury, M., Pocius, A. V., Eds. Elsevier Amsterdam, 2002 Chapter 12, pp 535-571. 

R. P. Eckberg, "Chemistry and Technology of Radiation Curable Silicone Release Coatings," in D. Satas, ed.,. Advances in Pressure Sensitive Adhesives, Satas Associates, Warwick, R.I., 1992. 

On that basis, the book intends to bridge current issues, aspects and interests from fundamental research to technical apphcations. In seven chapters, the reader will find an arrangement of latest results on fundamental aspects of adhesion, on adhesion in biology, on chemistry for adhesive formulation, on surface chemistry and pretreatment of adherends, on mechanical issues, non-destructive testing and durability of adhesive joints, and on advanced technical applications of adhesive joints. Prominent scientists review the current state of knowledge about the role of chemical bonds in adhesion, about new resins and nanocomposites for adhesives, and about the role of macromolecular architecture for the properties of hot melt and pressure sensitive adhesives. Thus, insight into detailed results and broader overviews as well can be gained from the book. 

Not only new techniques deserve attention, but also any new developments in old techniques, such as scanning electron microscopy (28). Scanning electron microscopy, for example, can now enhance the examination of the adhesive interface in greater detail. Two other old techniques have also found new applications in adhesive chemistry. One is dynamic mechanical analysis (29,30), which has been accepted for the study of pressure-sensitive adhesives and the curing mechanism of epoxy resins (31,32). The other is the use of a fluorescence probe to examine the curing mechanism (33). 

The chemistry of silicone resins and siloxane gums used to prepare silicone pressure sensitive adhesives is briefly reviewed. The thermal, dynamic mechanical and X-ray scattering properties of the silicone adhesives is presented. A specific morphological model for the silicone pressure sensitive adhesives is proposed based on the characterization data. The results for adhesives prepared from polydimethyl siloxane gums is compared to adhesive prepared from polydimethyl-co-diphenyl siloxane gums. 

Pressure-sensitive adhesives based on an entirely different type of chemistry, namely polythiol-ene adducts, have also been patented. A UV-cured system of this type has been reported to exhibit a 180 peel strength of 3.5 pounds/inch. 

There is a need to create silicones with controlled 3D structures for a variety of purposes. As one example, the class of silicone polymers known as MQ resins [4,5] exhibit very interesting surface activity and are utilized in high value formulations including liquid crystals [6], antifoaming compositions [7] and pressure sensitive adhesives [8]. There is significant interest for these applications in generating explicit MQ resins and other structures rather than mixtures of silicones, which is the current state of the art. Traditional chemistry does not fulfill these needs in most cases. 

The chemistry and structure of the tackifying terpene resins are developed by E. Ruckel al. These resins, produced commercially from pine turpentine, since the mid-Thirties, are formulated with natural rubber to produce pressure sensitive adhesives. More recently, the scope of their use has been broadened by formulation with elastomers and waxes for hot melt applications. Empirical application tests have developed a broad knowledge of utility but little science or predictability. By use of sophisticated high polymer techniques, polymerization mechanisms are used to explain how the minor structural differences between the beta-pinene and dipentene resins suit these resins respectively for pressure sensitive and hot melt adhesive usage. Again for use application the critical aspects of the formulation are its adhesive and cohesive properties as demonstrated by tack, shear and peel properties. 

Two commercial safety films were investigated, both of which were obtained from their primary manufacturers. These materials are typical poly(ethylene terephthal-ates) (PET), but the detailed product chemistry and composition are unknown. Both are manufactured with multiple layers of optically clear films and are installed by attachment to the interior surface of the glass using a pressure-sensitive adhesive. Hereafter, they are referred to as Films A and B, respectively. The films are used as received from the manufacturers. 

But these books usually focus either on the science and chemistry of adhesion and adhesives, on specific types of adhesives (such as pressure-sensitive adhesives, structural adhesives) or on industries that use adhesives and sealants, such as packaging, construction, metal bonding, etc. 

This area of adhesives technology is obviously where the polymer chemist plays a crucial role but a review of the basic chemistry of adhesives and of the formulation of adhesives is well beyond the scope of the present book. For such information the reader should consult references, such as Skeist s excellent Handbook of Adhesives [1] where these aspects are reviewed in detail for every imaginable chemical type of adhesive. There are also many specialized articles and chapters devoted to particular adhesive types such as those available on natural materials [2], solutions and latices [3], hot-melts [4], polyurethanes [5,6], phenolics [7], epoxies [8,9], acrylics [10,11], imide resins [12,13] and pressure-sensitive adhesives [14,15]. To translate from a particular chemical type of adhesive into a commercially available product reference may be made to the technical data sheets provided by the adhesives companies and to adhesive product directories, such as that produced by Shields [16]. 

Christensen SF, Everland H, Hassager O, AJmdal K (1998) Observations of peeling of a polyisobutylene-based pressure-sensitive adhesive. Int J Adhes Adhes 18 131 Creton C, Shull KR (2009) Probe Tack. In Benedek I, Feldstein MM (eds) Handbook of pressure-sensitive adhesives and products, fundamentals of pressure sensitivity. CRC Press, New York, pp 6-1-6-26 Dahlquist CA (1966) Tack. In The Ministry of Technology (ed) Adhesion fundamentals and practice. Gordon and Breach, New York, pp 143-151 Eaverarts AI, Clemens LI (2002) Pressure sensitive adhesives. In Chaudhury M, Pocius AV (eds) Surfaces, chemistry and applications adhesion science and engineering. Elsevier Science B.V, The Netherlands, pp 465-534... 

Kinning DJ, Schneider HM (2002) Release coatings for pressure sensitive adhesives. In Chaudhury M, Pocius AV (eds) Surfaces, chemistry and applications adhesion science and engineering. Elsevier Science B.V, The Netherlands, pp 535-571... 

Pressure-sensitive adhesives are widely used for securing dressings and devices to the skin surface. Most of these are now based on acrylic or silicone chemistries. 

Marlene Jones received her B.A. degree in Chemistry from Thiel College. She joined Hercules Incorporated in 1972 and is currently a Sales Development Supervisor in the Resins Division. Prior to this, Marlene held the position of Staff Chemist in the Adhesives Laboratory at the Hercules Research Center. Her experience in adhesives is primarily in the pressure-sensitive field. 

The chemistry of silicone sealants is much the same as that discussed above for silicone pressure-sensitive and mbber-based adhesives, with the exception of the MQ taddfier addition. The basic polymer for silicone sealants is that based upon poly (dimethyl siloxane)diol. This material can be cured by any one of a number of polyfunctional curing agents, all of which are based upon tetrachlorosilane. Thus, such materials as methyl triacetoxysilane or methyl trimethoxysilane can be used in conjunction with a poly(dimethyl siloxane)diol to yield a room... 

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