Modification by blending

Blends of NBR with other rubbers or with thermoplastic or thermosetting resins have been known for several decades. Modification by blending is undertaken to reduce costs, to improve the rheological properties of material, or to confer specific physical or chemical properties to the end product. 

The resins can be a novolak—hexa or a resole—novolak blend. In some appHcations Hquid resoles are used. Addition of alkylated phenol, oil, or cashew nutsheU Hquid (CNSL) reduces hardness and increases abrasion resistance. Modification by mbber improves the coefficient of friction and reduces brake fading. 

Modification of Alkyd Resins by Blending with Other Polymers... 

The wrinkle recovery angle provides a measure of the degree of chemical modification. This is calculated by blending a small sample and measuring the recovery to the flat configuration (180°). Whereas the untreated cotton recovers approximately 90°, the cross-linked cotton sample recovers 120—140°. If this is measured on dry fabric, it is termed conditional wrinkle recovery angle if on wet fabric, it is termed wet wrinkle recovery. At one point, wet wrinkle recovery was important, particularly in Europe. In the United States, the widespread use of clothes dryers has made conditional wrinkle recovery important. 

Modification ofP/astics. Many plastics, such as PVC, ABS, polypropylene, and nylon, ate blended with nitnle mbber to improve flexibiHty, toughness, or appearance. An oil-resistant thermoplastic elastomer has been prepared by blending nitnle mbber and polypropylene (24). 

Id. Thus, it is expected that in the modified PRP-EVA blend, probably due to interface modification by reactive processing, a transesterification between the pendant MAH group in MAH-PP, and acetate groups in the EVA elastomer, as predicted in reaction Scheme 1, the dispersed rubber particles become more efficient in craze initiation. 

Contrary to the structure similarity of the pheromones secreted by taxonomical related moths, some differences are necessary for their sexual communication systems to play an important role in their reproductive isolation. In addition to further modifications of the various structures, diversity of the lepidopteran sex pheromones is generated by blending multiple components. Innumerable pheromone blends are based not only on combinations of different components but also on variations in the mixing ratio. A pioneer study with Adoxophyes spp. (Tortricidae Tortricinae) had already proposed this concept in the early 1970s. While the smaller tea tortrix (A. honmai) and the Japanese summerfruit tortrix (A. oranafasciata) had been considered to be variant strains with different host preferences in the same species, Tamaki et al. found that females of the former pest insect in the tea garden secreted Z9-14 OAc and Zll-14 OAc in a ratio of 7 4 but females of the latter defoliator of apple trees secreted them in a ratio of 13 4 [127,128]. Furthermore, two other components (Ell-14 OAc and MelO-12 OAc) were subsequently identified from the former species [129]. 

The modification of PET with naphthalene-2,6-dicarboxylic acid and other additional comonomers is a common measure in bottle manufacturing. Copolyesters based on this compound show excellent barrier properties. Such materials can be produced by addition of the desired amount of comonomer during polymer processing or by blending PET with poly(ethylene naphthalate) (PEN). Additionally, PEN can also be modified by other comonomers such as isophthalic acid (IPA) to improve the flow properties and reduce the melting point. The high price of naphthalene dicarboxylic acid is the reason for its limited application. The overall cost may be reduced by using TPA or IPA as comonomers. 

The mechanical properties at low strain rates, dynamic mechanical properties, creep-recovery behaviour, thermal expansion and thermal conductivity of foams manufactured from blends of LDPE with an EVA and with an isoprene-styrene block copolymer were studied as a function of the LDPE content in the blends. The experimental results demonstrated important aspects related to the modification of the foam properties by blending. 16 refs. 

This section focuses on the modification of epoxy resins by blending with acrylonitrile butadiene (nitrile) resins. These are true alloyed blends since the nitrile rubber usually contains no groups that are normally reactive with epoxy groups. The nitrile molecules and the epoxy molecules intermingle as a blend to provide a single-phase alloy. If a large elastomer concentration is used, no phase separation will occur to form precipitates. 

Physical modification of milk fat by fractionating milk fat or by blending milk fat or milk fat fractions with other oils and fats results in products with an altered triacylglycerol composition, but one in which the fatty acids in milk fat maintain their original position in the triacylglycerol molecules (Kaylegian, 1999). 

ABS producers with existing emulsion or suspension capital may also produce high heat grades via imide modification. Mitsubishi Monsanto Chemical described methods of preparing high heat ABS by blending graft copolymer ... 

Polystyrene (PS) in its atactic and syndiotactic forms is a brittle thermoplastic, even in an orientated state [4]. To improve the toughness of aPS, impact modification has been practised for a long time, either by polymerizing the styrene in the presence of a polybutadiene rubber leading to high-impact polystyrene, commonly called HIPS, or by blending the polystyrene with multi-block copolymers, mainly of the styrene-butadiene-styrene (S-B-S) type. 

For many applications, the toughness of sPS is insufficient, which has thus led to many attempts in the past to increase its toughness significantly compared with HIPS by blending with rubbers. In the stress field of softer or harder particles than the sPS matrix, typical deformation processes inherent to the matrix are initiated. For rubber modification it is important that the application or test temperature is above the glass transition temperature of the rubber, otherwise the stiffnesses of the two components hardly differ from each other and local stress fields around the rubber particles are not formed. The formation of numerous deformation zones round the rubber particles is generally the basis of impact modification [10]. 

---