Achieving a Balance of Properties

In the past, impact modifiers often came with side effects, such as a reduction in tensile strength, modulus, heat distortion temperature, weathering performance, and clarity. It has been the objective of impact modifier suppliers to offer improved impact strength, even at low temperatures, without these or other disadvantages. Advances in blending and compatibilising technology now enable suppliers to use rather more complex formulations. 

The latest additives are claimed to preserve key properties such as modulus and in some cases even to improve them. Some impact modifiers also act as process aids. The emphasis is now on the overall balance of performance rather than just achieving an increase in toughness. As a result impact modifiers have become more popular. They are employed to toughen rigid PVC and the polyolefins, and can also upgrade the performance of engineering thermoplastics in automotive applications and domestic appliances. 

These trends are illustrated by DuPont Dow Elastomers range of Engage polyolefin elastomers, intended as impact modifiers for polypropylene in automotive bumpers and fascias. They combine stiffness with ductility, and are claimed to give very good low temperature impact strength. Engage 8842 is said to have a particularly wide range of applications. 

DuPont s Fusabond AEB-560D is a modified ethylene-acrylate copolymer for use in polyamides. It is claimed to be a cost-effective toughener, more effective than maleic anhydride terpolymers and usable at low temperatures, while improving mould flow, with less of an adverse effect on the flexural modulus. 

Clarity in impact-modified formulations has also been addressed. High clarity in bottles, containers and glazing generally requires the impact modifier to have a very similar refractive index to the base polymer over all the relevant temperatures. In practice most modifiers undergo considerable drift in refractive index with changes in temperatme, so this is a major challenge. Exact , an octene-based plastomer from Dex-Plastomers, has been used with some success to toughen clear polypropylene copolymer bottles. 

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Visual and Manual Tests. Synthetic fibers are generally mixed with other fibers to achieve a balance of properties. Acryhc staple may be blended with wool, cotton, polyester, rayon, and other synthetic fibers. Therefore, as a preliminary step, the yam or fabric must be separated into its constituent fibers. This immediately estabUshes whether the fiber is a continuous filament or staple product. Staple length, brightness, and breaking strength wet and dry are all usehil tests that can be done in a cursory examination. A more critical identification can be made by a set of simple manual procedures based on burning, staining, solubiUty, density deterrnination, and microscopical examination. 

Diluents are commonly used to reduce the viscosity of epoxy systems to aid handling, improve ease of appHcation, and to faciUtate higher filler loa ding to reduce formulation cost. This, however, is achieved at the expense of other properties. To achieve a balance of properties, careful selection of diluent is needed. Table 1 quaUtatively shows which diluent should be considered for minimal deterioration of properties. 

Historically, block copolymers have found utility as a means to achieve a balance of properties between chemically different homopolymers (7-8). 

Vulcani2ation is a chemical process for improving an elastomer compound s performance. However, in most cases not all of the desired properties reach their optimum levels simultaneously. One of the mbber compounder s key responsibiHties is to achieve a balance of the most important property requirements by the proper selection of cure system (chemical) and time—temperature cure cycle (physical). 

Achieving a balance of sealant properties is the most severe test of the formulator s skill. 

Epoxy resins must be cured with cross-linking agents (hardeners) or catalysts to develop desired properties. Cross-linking takes place at the epoxy and hydroxyl groups that are the reaction sites. Useful agents are amines, anhydrides, aldehyde condensation products, and Lewis acid catalysts. To achieve a balance of application properties and initial handling... 

As the fundamental building block for printed circuits, base materials must meet the needs of the printed circuit board (PCB) manufacturer, the circuit assembler, and the original equipment manufacturer (OEM). A balance of properties must be achieved that satisfies each member of the supply chain. In some cases, the desires of one member of the supply chain conflict with another. For example, the need for improved electrical performance by the OEM, or improved thermal performance by the assembler, may necessitate the use of resin systems that require longer multilayer press cycles or less productive drilling processes, or both. 

Blending different biofibers could result in biocomposites with balanced properties. Engineered biofibers, defined as the suitable blend of surface-treated bast and leaf fibers as shown in Figure 13.8, have been studied and reported. By manipulating the blend ratio of biofibers, an optimum balance in mechanical properties of the resulted biocomposites could be attained. For example, kenaf- and/or hemp-based composites exhibit excellent tensile and flexural properties, while leaf fiber (PALF) composites have high impact properties. The combination of bast and leaf fibers is expected to achieve a balance of flexural and impact properties of the targeted biocomposites [49]. 

In most of their applications, elastomers are used in compounds where CB plays the key role in reinforcing mechanical properties. Not all properties are improved when adding CB particles to an elastomer and a balance of properties has to be achieved with respect to the application. In rubber compounds, CB amounts to 20-30% volume fraction. 

Biaxial Orientation. Many polymer films require orientation to achieve commercially acceptable performance (10). Orientation may be uniaxial (generally in the machine direction [MD]) or biaxial where the web is stretched or oriented in the two perpendicular planar axes. The biaxial orientation may be balanced or unbalanced depending on use, but most preferably is balanced. Further, this balance of properties may relate particularly to tensile properties, tear properties, optical birefringence, thermal shrinkage, or a combination of properties. A balanced film should be anisotropic, although this is difficult to achieve across the web of a flat oriented film. 

With respect to the action of the enzyme itself, a loss of weight on account of cellulose hydrolysis, as well as loss in strength properties, occurs. Therefore, control of concentrations, temperature, and other processing conditions is important to achieve a product having the proper balance of properties. 

For the correlation bands obtained by a convolution of many shake-up lines, the size-consistency and size-intensivity requirements imply a convergence towards some asymptotic profile, when going to the polymer limit. This must ideally be achieved through a balance of the scaling properties of the individual shake-up lines, and the dispersion of the intensity of Ih lines over a rapidly increasing number of excited states with increasing system size. 

The direct optimization of a single response formulation modelled by either a normal or pseudocomponent equation is accomplished by the incorporation of the component constraints in the Complex algorithm. Multiresponse optimization to achieve a "balanced" set of property values is possible by the combination of response desirability factors and the Complex algorithm. Examples from the literature are analyzed to demonstrate the utility of these techniques. 

The successful application of food-grade biopolymers in the formulation of the next generation of smart delivery systems requires sound insight into the various intermolecular and colloidal interactions involved in the food matrix, along with some knowledge of the bioavailability in vivo. Furthermore, the impact of incorporated nutraceuticals on all the properties of a formulated functional food — appearance, physical/chemical stability, texture, mouthfeel, taste, flavour, bioavailability, and health impact — need to be simultaneously considered and addressed in order to achieve a balanced and acceptable solution for consumers. 

Although development of a formulation for a specific product and process requires a great deal of knowledge and experience, there are some basic rules typical of FKM compounding. The levels of acid acceptor (MgO) and activator (Ca(OII)2) in the bisphenol cure system strongly affect not only the cross-linked network as reflected by the physical properties of the material, but also the behavior of the compound during vulcanization. Therefore, the curing system must be optimized to achieve the best balance of properties. 

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