Fillers Polymers Characteristics

Polymer-based composites can be divided into thermoset and thermoplastic composites, which due to their different properties show diverse fracture mechanism. Due to tight three-dimensional molecular network structure of the most of thermoset matrixes such as epoxy resins, they exhibit inherent brittle fracture behavior and poor 

Tang et at [36] investigated the mechanical properties of epoxy resins filled with different amoxmts of soft rubber particles and/or rigid silica nanoparticles, with special focus on the related mechanical and fracture behaviors. Additionally, increases in fracture toughness by the rigid particles addition in polypropylene [37,38] and polyethylene [38, 39] were addressed in some researches. 

Lei and Wu [40] prepared wood plastic composites based on in-sifw-formed polyethylene terephthalate (PET) sub-micro-fibril (less than 500 nm in diameter) reinforced high-density polyethylene (HDPE) matrices through strand die extrusion and hot strand stretching. The PET fibrils obviously increased mechanical properties of the 

In addition to the discussed factors, the type of loading (quasi-static or dynamic) affects the mechanical response and fractme behavior of particulate polymer composites. 

The development of the WPCs for load-bearing structural applications necessitates the characterization of their strain rate-dependent mechanical properties. In this regard, the effect of strain rate on flexural properties of WPG was addressed by Tamrakar and Lopez [49]. The strain at failure was not significantly influenced by the strain rate variation. A prediction model for the effects on strain rate on the modulus of elasticity (MOE) of WPG material was demonstrated based on the viscoelastic standard solid model. Yu et al. [50] analyzed the variability of the dynamic young s modulus of WPG, which was measured by different non-destructive test (NDT) methods. They also estimated the correlativity between the dynamic Young s modulus and the static MOE of WPG. 

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Furthermore, the effect of hydrated fillers on polymer fire retardancy will depend not only on the nature of the filler, including its particle characteristics (size, shape, and purity) and decomposition behavior, but also on the degradation mechanism of the polymer, together with any filler/ polymer interactions that might occur, influencing thermal stability of the polymer and possible char formation. 

As seen from Fig. 1, theory and practice coincide. The methods and equations, given in Sect. 3.1-3.3 allow us to calculate the head and consumption characteristics of the melted thermoplast, filled with a disperse inert filler, in particular, a mineralorganic one, at various pre-set temperatures and concentrations by using a single known head and consumption basic polymer characteristic, measured at any fixed temperature. The authors of this review have developed appropriate algorithms and programs for carrying out these calculations. 

A special group of modem polymeric materials is represented by composites with polymer matrix, also simply called polymer composites. The latter contain certain particulate or fibrous fillers. Molecular characteristics of polymer matrix play important role in the optimum properties of composites. 

Fillers are particulate materials that are added to raw polymers to modify the polymer characteristics they are widely used in polymer technology and play a particularly significant role in modifying the properties of rubber. In this article, various effects of fillers are discussed, with some emphasis on the formulation of rubber for bonding to metals (see Rubber to metal bonding - basic techniques). 

The electrical conductivity of polymer composites is affected by several factors, namely polymer characteristics, filler features, the interactions among the phases, the processing technique, and the multiphase morphology (Strumpler and Glatz-Reichenbach 1999 Boudenne et al. 2011 Mittal 2012). All these aspects are further reviewed here. 

After the discovery of carbon nanofiber (CNF), most of the works are focused on the use of CNF as thermal, electrical and mechanical reinforcing filler to improve the polymer characteristics [48, 49], A significant amount of work has been conducted by using the one dimensional carbon fillers like CNT and CNF. The one dimensional filler may connect more polymer chains and afford more effective load transfer, leading to an improvement of mechanical properties [50]. One dimensional fillers can easily transfer the loads or reduce it than spherical fillers. Well dispersed polymer composites filled with CNT or CNF can be achieved by using the fine twin-screw extrusion, surfactant, oxidation of fillers and incorporation of functional groups on the surface of the fillers. The transmission electron microscopy (TEM) images of the fillers are shown in Fig. 4. 

To describe the change in reptation dynamics of the chains as a function of nanoparticle volume fraction, a percolation model was used. At the percolation threshold, a physical network formed by interconnection of immobilized chains on individual nanoparticles penetrates the entire sample volume. In this case, only physical cross-links are considered and the terminal relaxation time reaches the value characteristic for the life time of the physical filler-polymer bond. Thus, the relaxation time near the percolation threshold is expressed in the form [44] ... 

The percolation threshold, cpc, is the fiUer loading level at which the polymer first becomes conductive, which is generally considered to be a value of about 10 S/cm. Comprehensive experimental and theoretical treatments describe and predict the shape of the percolation curve and the basic behaviors of composites as a function of both conductive filler and the host polymer characteristics (36-38). A very important concept is that the porous nature of the conductive carbon powders significantly affect its volume filling behavior. The typical inclusive stractural measurement for conductive carbon powder porosity is dibutyl phthalate absorption (DBF) according to ASTM 2314. The higher the DBF, the greater the volume of internal pores, which vary in size and shape. The crystalhnity of the polymer also reduces the percolation threshold, because conductive carbons do not reside in the crystalhtes but instead concentrate in the amorphous phase. Eq. (2) describes the percolation curve (39). 

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