Pressure sensitive adhesives mechanical properties

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

Fillers provide films with conductive properties, influence their surface properties, affect their permeability, mechanical and optical properties, and affect their durability against environmental exposure. Various technologies are used to produce conductive films. These include lamination to metal foils (in-plant, using pressure sensitive adhesives), surface coating, and addition of conductive materials. Conductive films are widely used in packaging to limit static electricity. 

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. 

Bon, Keddy, and coworkers [109] demonstrated that soft armored polymer latex made via Pickering miniemulsion polymerization [i.e., poly(lauryl acrylate) armored with Laponite clay discs] could be used as a nanocomposite additive in standard poly(butyl acrylate-co-acrylic acid) waterborne pressure-sensitive adhesives (PSAs), leading to marked mechanical property enhancements (see Fig. 13). 

B. C. Copley, "Dynamic Mechanical Properties of Silicone Pressure Sensitive Adhesives," in Ref. 14. 

The fourth and fifth papers have to do with properties of pressure-sensitive adhesives. In particular, the matter of how the materials composing pressure-sensitive adhesives (rubbers and resins) interact and phase separate to produce the phenomenon of tack or pressure-sensitivity is addressed. Both studies use dynamic mechanical measurements to uncover phasing - one in a silicone and the other in natural and styrene-butadiene rubber systems tackified with various resins. 

Dynamic Mechanical Properties of Silicone Pressure-Sensitive Adhesives... 

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. 

Blends of the MQ resin with high molecular weight siloxane gum which may be cross-linked by the addition of benzoyl peroxide result in silicone pressure sensitive adhesives. The purpose of this work is to examine the dynamic mechanical properties of the formulated adhesives in an effort to understand how the silicone resins and gums interact to form a pressure sensitive adhesive. A specific morphological model as suggested by experimental results will be discussed. 

Viscoelastic characteristics of polymers may be measured by either static or dynamic mechanical tests. The most common static methods are by measurement of creep, the time-dependent deformation of a polymer sample under constant load, or stress relaxation, the time-dependent load required to maintain a polymer sample at a constant extent of deformation. The results of such tests are expressed as the time-dependent parameters, creep compliance J t) (instantaneous strain/stress) and stress relaxation modulus Git) (instantaneous stress/strain) respectively. The more important of these, from the point of view of adhesive joints, is creep compliance (see also Pressure-sensitive adhesives - adhesion properties). Typical curves of creep and creep recovery for an uncross-Unked rubber (approximated by a three-parameter model) and a cross-linked rubber (approximated by a Voigt element) are shown in Fig. 2. 

In this article we review this informationO0-i4) and explain how the dynamic mechanical properties of rubber-resin blends are related to the performances of pressure-sensitive adhesives. (See also Chapter 2 by Krieger.)... 

So far, we have discussed the dynamic mechanical properties of elastomers which are used for making pressure-sensitive adhesives. In the following sections, we shall discuss the dynamic mechanical properties of tackifying resins and pressure-sensitive adhesives. 

So far we have discussed the dynamic mechanical properties of elastomers and tackifying resins separately. We have also examined the dynamic mechanical properties of the commercial tape and label adhesives and defined their requirements for good pressure-sensitive adhesives. We will explain how to obtain PSA with the specific requirements in T, G (co), and G"(w) values from the nontacky elastomer and glassy tackifying resin. First, the simple two-component formulations will be examined for various elastomeric systems. 

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. 

As one begins to read the literature on adhesives and especially pressure-sensitive adhesives, it is easy to become confused about the relative importance of the adhesive/substrate interface and the mechanical or rheological properties of the... 

For example, Christenson et al. [3,19] performed a detailed study of polyisobutylene-based pressure-sensitive adhesives. Although these authors did not postulate a specific detachment criterion, they did extensive work characterizing the linear viscoelastic properties, the tensile stress-strain properties, and the peel force. In addition, they conducted detailed visualization of the deformation of the adhesive during peel and therefore, could assess the ability to predict the peel force from the mechanical properties of the adhesive and the visually observed detachment strain. In this work, the adhesive consisted of a blend of high and low molecular weight polyisobutylene. They showed that when they used the Giesekus model as the constitutive equation for the adhesive, they could accurately describe the stress-strain curves of the adhesive and the peel force was well predicted by the integral of the stress-strain curve up to the measured detachment strain. Their results are summarized in Table 1. 

Adhesive coating Ease of adhesive coating after surface treatment or adhesive modification Ease of postfabrication Smooth surface Regular cellular structure Wide range of mechanical properties Pressure-sensitive adhesive coated applications, tapes, strips, pad, joints and gaskets... 

Chu has also characterized numerous commercial pressure sensitive adhesives and shown that elastic modulus and glass transition temperature are key viscoelastic properties in characterizing pressure sensitive adhesive performance. An excellent review outlining the characterization of pressure sensitive adhesive by dynamic mechanical measurements and discussing how these data can aid in the formulating of adhesives has been recently published by Chu. ... 

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