Phase adhesion

The morphology of a typical urethane adhesive was previously shown in Fig. 3. The continuous phase usually comprises the largest part of the adhesive, and the adhesion characteristics of the urethane are usually controlled by this phase. From a chemical standpoint, this continuous phase is usually comprised of the polyol and the small amount of isocyanate needed to react the polyol chain ends. A wide variety of polyols is commercially available. A few of the polyols most commonly used in urethane adhesives are shown in Table 2. As a first approximation, assuming a properly prepared bonding surface, it is wise to try to match the solubility parameters of the continuous phase with that of the substrate to be bonded. The adhesion properties of the urethane are controlled to a great extent by the continuous phase. Adhesion to medium polarity plastics, such as... 

PS and PB homopolymers are immiscible. Any added PB-PS block copolymer in a PS-PB blend will have one sequence miscible in PS and one sequence miscible in PB, hence they will localise at the interface. As a consequence, the interfacial energy will decrease, greatly helping dispersion and providing phase adhesion, thus a transfer of mechanical properties. 

Many factors contribute to the toughness of a polyphase BMI/thermoplastic system, such as solubility parameters, phase adhesion, phase morphology, particle size and particle size distribution. Another important factor is the molecular weight of the thermoplastic modifier. It has been demonstrated for a particular poly(arylene-ether) backbone that high molecular weights increase the toughness of the blend system more than the low molecular weight counterparts (92). 

As binary PPE/SAN blends form the reference systems and the starting point for the foaming analysis, their miscibility will be considered first. As demonstrated in the literature [41, 42], both miscibility and phase adhesion of PPE/SAN blends are critically dependent on the composition of SAN, more precisely on the ratio between styrene and acrylonitrile (AN). Miscibility at all temperatures occurs up to 9.8 wt% of AN in SAN, whereas higher contents above 12.4 wt% lead to phase separation, independent of the temperature. Intermediate compositions exhibit a lower critical solution temperature behavior (LCST). Taking into account the technically relevant AN content SAN copolymers between 19 and 35 wt%, blends of SAN and PPE are not miscible. As the AN content of the SAN copolymer, selected in this work, is 19 wt%, the observed PPE/SAN blends show a distinct two-phase structure and an interfacial width of only 5 nm [42],... 

Compatibilization/nanostructure formation for achieving a finer blend morphology by the reduction of both the interfacial tension and coalescence, and for ensuring an improved phase adhesion/nanostructure between the blend partners. Thus, the incorporation of the dispersed blend phase into the cell walls should be enhanced while the number of possible nucleating sites is simultaneously increased. 

The aim of this section, therefore, is to correlate systematically the compatibilization of PPE/SAN 60/40 blends by SBM triblock terpolymers with the foaming behavior of the resulting blend. The reduction of the blend phase size, the improved phase adhesion, a potentially higher nucleation activity of the nanostructured interfaces, and the possibility to adjust the glass transitional behavior between PPE and SAN, they all promise to enhance the foam processing of PPE/SAN blends. 

These single-phase hybrids are very different from the two-phase toughened epoxynitrile adhesives that are discussed in Chap. 8. These two-phase adhesives have redefined structural adhesives to a great extent and have opened the door to many applications that were previously not possible because of the epoxy resin s inherent rigidity. The polymer mixtures that exist as separate phases provide significant increases in toughness but have only a small improvement in elongation at typical use levels. 

Rubber-resin heterophase systems are classified as (1) resin as the disperse phase, (2) rubber as the disperse phase, (3) grafted rubber latex particles as the disperse phase, and (4) filled graft rubber as the disperse phase. Adhesion mechanisms related to these systems are discussed. Special emphasis is made on the last two systems which involve grafting. The graft rubber isolated from the fourth system is characterized. The graft rubber is shown to function as a compatibilizer and as an adhesive or a coupling agent for the rubber-resin interface. 

Owing to the extremely high importance of grafting for the particle size, the particle structure, the rubber efficiency and the phase adhesion, numerous attempts have been made to increase the graft yield. 

The presence of boron atoms in CPG surfaces frequently influences the properties of stationary phases adhesively deposited on CPG used as support. It is especially well evidenced for phases whose molecules form a monolayer in which they are parerely oriented towards a support surface in the gas/solid or phase/solid interface [74]. The properties of... 

A typical characteristic of physically setting adhesives is the evaporation of solvents or heatup to a molten state. Application is then in liquid form (solvent adhesives, contact adhesives, dispersion adhesives, hotmelt adhesives) or from the solid phase (adhesive films, laminate adhesives). In all of these types there is a liquid state during processing from which emissions are always a possibility due to the volatility of the basic polymer or other adhesive components. 

One possible way of reducing interfacial tension and improving phase adhesion between PP-based blend phases is to use a selected copolymeric additive that has similar components to the blend, as a compatibilizer in the blend system. Well-chosen diblock copolymers, widely used as compatibilizing agents in PP-based blends, usually enhance interfacial interaction between phases of blends (15, 16), reduce the particle dimensions of the dispersed phase (16, 17), and stabilize phase dispersion against coalescence (16-18) through an emulsification effect, thus improving the mechanical properties (15-19). 

PPE, with SAN, SMMA, SAA or SMA Miscibility of copolymers with PPE when the amount of comonomer is small. The interfacial energy between the blend components was significantly reduced by adding either a PS-b-PMMA, or PS-b-PEB-b-PMMA. The copolymers had a profound influence on morphology, phase adhesion and mechanical properties of the blend. Gottschalk et al., 1994... 

In view of the association that exists between polymer blends and filled materials with regard to phase adhesion and phase... 

Miscibility refers to the molecular mixing of the components down to the level adequate to yield macroscopic properties expected of a single phase system (01a-bisi et al., 1979). Mutual miscibility or immiscibility of the two components in the melt and in the amorphous state of a crystallizable binary blend plays a vital role in the blend s microstracture, crystallization behavior, and degree of dispersion of one component in the matrix of another as well as inter-phase adhesion (Silvestre etal., 1996). 

Combinations of PEI resins with polyamides (nylons) also produce phase-separated blends with fine particle morphology and good mechanical properties, hkely arising from phase adhesion between the two resins... 

Figure 6.4 Schematics of deformation processes in particie composites without strong phase adhesion [6] ...

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