Properties of Polyurethane Adhesives

The physical properties of polyurethane adhesives result from a special form of phase separation which occurs in the cross-linked polyurethane stmcture. The urethane portions of polyurethanes tend to separate from the polyol portion of the resin, providing good shear strength, good low temperature flexibiUty, and high peel strength. Catalysts such as dibutyltin dilaurate [77-58-7], stannous octoate [1912-83-0], l,4-diazabicyclo[2.2.2]octane... 

The 3D architecture obtained by the introduction of 3D molecules should lead to new approaches to enhancing simultaneously the shear and peel properties of polyurethane adhesives and coatings, which otherwise is difficult to achieve. 

In addition to providing the properties of polyurethane chemistry, the authors reported that HNIPUs also exhibit the chemical resistance of epoxy binders. Potential uses of HNIPUs include commercial application in paints, varnishes, adhesives, caulking compounds, flooring/industrial coatings, foams, and composite materials. 

Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities. The performance properties of polyurethane can be widely modified by selecting appropriate raw materials, catalysts and auxiliary compounds, by employing various production methods and/or by employing various methods for further processing and/or for shaping the final products. Therefore, polyurethanes have wide applications such as elastomer, coating, adhesive, foam, and leather. 

Sepiolite was subjected to a thermal treatment which removes crystallization water at 500 C and constitution water at 850°C. When these changes occur, they are accompanied by crystal folding which introduce substantial changes in the structure and interaction capabilities of sepiolite. Treated and untreated sepiolites were used in the preparation of a polyurethane adhesive to determine if the modification impacts the properties of the adhesive such as its interaction with polymer essential for its performance in adhesive. Figure 19.1 shows the effect of treatment... 

The dynamic mechanical relaxations in the high temperature region are very weak and the glass transition was indistinguishable from the melting point (Fig. 4). However, the mechanical properties of polyurethanes with chemically crosslinked hard segments were quite different from uncrosslinked polyurethanes. In the linear adhesives (73-14 and 73-15), the rubbery plateau ends at the melting point of the... 

Lin, H., et al., Synthesis, surface, and cell-adhesion properties of polyurethanes containing covalently grafted RGD-peptides. Journal of Biomedical Materials Research, 1994, 28, 329-342. 

The adhesive properties of polyurethanes may be attributed to the polar nature of the macromolecular compounds used in their formulation. Furthermore, the isocyanates present in the polyurethane compositions may react with any active hydrogen present in the adherent or with the films of water often present on the surfaces of materials such as ceramics, glass, and metals. These types of reactions result in enhanced anchoring of the adhesive and attainment of high bond strength. 

An example of a polyurethane adhesive used for surface mounting components consists of Mondur M cured with castor oil or with other polyols. The molecular weight and properties of polyurethanes are optimized when one equivalent weight of the isocyanate reacts with one equivalent weight of the polyol. The equivalent weights are based on the percent of hydroxide of the polyol and the percent of isocyanate of... 

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]. 

S.4.4 Physical and mechanical properties of polyurethane networks and surfactant additives. The cohesion and adhesion properties of the cured polymers were investigated to elucidate the influence of KEP-2 on the physicsd and mechanical properties of polyurethane networks based on PPG in the presence of individual ohgomers. 

For glulam beams and load bearing timber structures, standards are numerous and stringent. A significant distinction is made between adhesives types, taking into account their chemical and mechanical properties. In this way, it is necessary to consider EN 301 (2006) [6] for aminoplastic and phenolic adhesive and EN 15425 (2008) [13] for polyurethane adhesives. Associated test methods are described to assess the critical properties of these adhesives and to evaluate the differences between them in more or less the same conditions. 

The presence of ionic groups in polyurethanes is known to drastically change the mechanical properties of polyurethanes (18), but the remarkable effects on adhesion have not been reported previously. The presence of such ionic bonds is consistent with the fact that adhesion in these systems is markedly reduced by soaking a few days in water, which would solvate the ionic clusters (18) and reduce their effectiveness in promoting adhesion. It is noteworthy that strong adhesive bonds reform on drying (19). ... 

REASONS FOR ADHESIVE PROPERTIES OF POLYURETHANE AND DIISOCYANATE-BASED ADHESIVES... 

The properties of cyanoacrylate adhesives have been discussed in detail in the previous sections of this chapter. The evaluation of these adhesives is complemented in this section by comparisons with other structural adhesives. A specific comparison has been made of cyanoacrylate adhesives with a two-part epoxy, EC 2216 B/A, and a two-part polyurethane, EC 3549 B/A, all sold by 3M. The substrates on which the adhesives were tested were aluminum, polystyrene, and chloroprene. The results for room temperature water immersion, 90°F/90% relative humidity, and 150°F oven aging are shown in Tables XVI and XVII. 

Tremendous efforts have been put into surface modification of polyurethane biomaterials to promote cell adhesion [41] and/or depress platelet adhesion [42,43], biofihn formation [44], or protein adsorption [45]. CA is the quickest indirect evidence of confirming these surface modifications. Cooper et al. [41] prepared a series of polyurethanes with surfaces functionalized with three hexapeptides to improve cell adhesion. The polar peptides on the surface increase the hydrophilicity and thus decreased CAs were observed. Again, CA is only an indirect proof of a successful surface modification since there are many factors that contribute to a change in CA. Many other surface characterization techniques must be combined to obtain a fuU picture of the surface properties of polyurethane biomaterials. 

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