Reinforcement performance

To be effective, the reinforcement must form a strong adhesive bond with the plastics for certain reinforcements special cleaning, sizing, finishing, etc. treatments are used to improve bond. Also used alone or in conjunction with fiber surface treatments are bonding additives in the plastic to promote good adhesion of the fiber to the plastic. 

Applicable to RPs is the aspect ratio of fibers. It is the ratio of length to diameter (L/D) of a fiber. In RP fiber L/D will have a direct influence on the reinforced plastic performance. High values of 5 to 10 provide for good reinforcements. Theoretically, with proper lay-up the highest performance plastics could be obtained when compared to other materials. To maximize strength and modulus of RPs the long fiber approach is used. 

Different types of reinforcement construction are used to meet different RP properties and/or simplify reinforcement layup for certain fabricating processes to meet design performance requirements. They include woven, nonwoven, rovings, and others (Table 3.3). These different constructions are used to provide different processing and directional properties. 

A fibrous material extensively used in RPs are the mat constructions. They consist of different randomly and uniformly oriented products (1) chopped fibers with or without carrier fibers or binder plastics (2) short fibers with or without a carrier fabric (3) swirled filaments loosely 

There are reinforcement preform constructions. A preform is a method of making chopped fiber mats of complex shapes that are to be used as reinforcements in different RP molding fabricating processes (injection, etc.). Oriented patterns can be incorporated in the preforms. 

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Approximately, the reinforcement performance of the fibres increases from the top to the bottom of the table. 

Most SRIM resins have several characteristics in common their liquid reactants have room-temperature viscosity below 200 cps their viscosity-cure curves are sigmoidal in shape, the typical mold-fill time being 10-90 sec and their demold time is from 60 to 180 sec, varying with catalyst concentration. The low viscosity of SRIM resins and their relatively long fill times are crucial in allowing them to penetrate and flow through their reinforcing performs. 

Unfortunately, both these modifications are complicated processes to carry out. There is also a negative side effect of using modified cellulose whiskers. It has been shown that modified whisker have less reinforcing effect than unmodified whiskers. Grunert and Winter [74] prepared nanocomposites with a hydrophobic thermoplastic matrix using trimethylsilylated cellulose whiskers. They found that unmodified whiskers showed a better reinforcing performance than the trimethylsilylated whiskers. Similarly, the mechanical properties of nanocomposites containing chemically modified chitin whiskers from crab shell were found to be inferior to the unmodified nanocomposites [75]. 

These findings can perhaps be explained by reference to the fact that in the industries that have high external risks the extensive historical use of procurement and supply tools and techniques reinforces performance satisfaction since it mitigates the risks that have to be managed and ensures the fulfilment of functional level objectives. The industries with the highest risks appear, therefore, to be using tools and techniques more extensively and with higher satisfaction levels than the medium risk industries, where the lower risks reduce the need for such an extensive use of tools and techniques. 

Daniels, A.C. and Rosen, T.A., Performance Management Improving Quality and Productivity through Positive Reinforcement. Performance Management Publications, Inc., Tucker, Georgia (1987)... 

Three-Dimensional Braid (3-D braid) A recent development in building reinforcement performs for complex shapes that permits the placing of reinforcing fibers in three orthogonal (or nonorthogonal) directions so as to best support multidirectional stresses expected to act on the finished part in service. 

Transactional leadership can be active or passive. In the active form, the leader takes the initiative to communicate expectations and then monitors and reinforces performance. The research literature calls this constructive transactional leadership. In the passive version, the leader waits until something goes wrong and then responds with the appropriate consequence. This is called corrective transactional leadership or management by exception. The literature is very clear about the superiority of constructive to corrective transactional leadership. Unfortunately, few leaders avail themselves of the power of active transactional leadership, opting instead for the relatively weak, passive version. ... 

In sharp contrast with carbon black, there is no standard classification for commercially available silica but elementary particle size and the morphology of the reinforcing object (that we call the "cluster" in the case of silica, keeping the term "aggregate" for carbon black) are recognized as two important parameters for reinforcement performance. However, surface character-isdcs play a larger role in the case of silica than for carbon black, thanks to the rich surface chemistry of silica particles. 

Silicone rubber and, in general polar polymers, are by nature materials of choice for preparing silica filled systems however limited to niche applications, with respect to the range of properties that such specialty polymers may offer. In order to develop optimum reinforcing performance with more common diene elastomers, silica must be chemically treated as we will see below, because contrary to carbon blacks, silica particles do not develop spontaneous strong interactions with nonpolar polymers. It is nevertheless interesting to see that, even with comparable size and structure, pure silica does not affect the mechanical properties of vulcanized rubber compounds in the same manner as carbon black. 

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