The Polymers Structure and Mechanical Properties Prediction

Polymers are often enough used as films, which were prepared from polymer solutions. As it is known [6], a solution change results to the essential variations of film samples of the same pol5mer. Therefore, a film sample structure prediction as a function of solvent characteristics, from which it was prepared, is the goal solution first stage. It is obvious, that the solubility parameter of solvent 8 is its characteristic the best choice [7, 8], The fractal dimension structure 7 was chosen as its characteristic [9], which can be determined according to the Eqs. (1.9) and (2.20). 

In Fig. 13.1, the dependence of on 6 for 9 used for films preparation solvents is adduced, where the value 6 was accepted according to the literary data [10]. 

FIGURE 13.1 The dependence of PAST films structure fractal dimension on solubility parameters d of solvent, from which a film was prepared [1], 

The polymer solubility parameter 5 value can be determined by its cohesion energy density W as follows [10]  

For PASF IF = 385 MJ/m [10], from which 5p for this polymer is equal to 9.61 (cal/cm ). As it follows from the plot adduced in Fig. 13.1, the r/j, sharp increase occurs at difference absolute value 5p-5 = A5 growth and the least value is reached at the condition 5 = 5 ( A5 = 0) [1]. This allows to obtain the following relationship for considered films value r/j, estimation [1]  

---

Macosko and Miller (1976) and Scranton and Peppas (1990) also developed a recursive statistical theory of network formation whereby polymer structures evolve through the probability of bond formation between monomer units this theory includes substitution effects of adjacent monomer groups. These statistical models have been used successfully in step-growth polymerizations of amine-cured epoxies (Dusek, 1986a) and urethanes (Dusek et al, 1990). This method enables calculation of the molar mass and mechanical properties, but appears to predict heterogeneous and chain-growth polymerization poorly. 

In the last decade, major technological developments have occurred in the production of polymer fibers with high mechanical strength and stiffness. In concert with these efforts, studies have been directed toward a better understanding of the relationship among chemical composition, physical structure and mechanical properties. One goal is to develop predictive structure-property models to develop marketable technologies. The discussion that follows includes examples of the types of nucroscopy... 

At present, there are at least two approaches to the investigation of the cellular structure of foamed polymers. In the first one, which may formally be called a graphical approach, attempts are made to draw conclusions on the macroscopic properties of foamed polymers from morphological parameters such as the geometry and stereometry of cells of various sizes, shapes and types. The second approach, which may be referred to as physicochemical, attempts to explain and predict polymer morphology from the data on the chemical composition of the polymer matrix and the mechanisms of foaming... 

The complexity of polymeric systems make the development of an analytical model to predict their structural and dynamical properties difficult. Therefore, numerical computer simulations of polymers are widely used to bridge the gap between the theoretical concepts and the experimental results. Computer simulations can also help the prediction of material properties and provide detailed insights into the behaviour of polymer systems. A simulation is based on two elements a more or less detailed model of the polymer and a related force field which allows the calculation of the energy and the motion of the system using molecular mechanisms, molecular dynamics, or Monte Carlo techniques [63]. 

The mechanical and viscoelastic behaviours of natural rubber based blends and interpenetrating polymer networks (IPNs) are fimctions of their structures or morphologies. These properties of blended materials are generally not constant and depend on the chemical nature and type of the polymer blends, and also enviromnental faetors involved with any measurements. Preparations of natural rubber blends and IPNs are well known as effeetive modifieation methods used to improve the original meehanieal and viscoelastie properties of one or both of the eomponents, or to obtain new natural rubber blended materials that exhibit widely variable properties. The most common consideration for their mechanical properties include strength, duetility, hardness, impact resistance and fracture toughness, each of which can be deformed by tension, compression, shear, flexure, torsion and impaet methods, or a eombination of two or more methods. Moreover, the viseoelastieity theory is a way to predict the behaviours of deformation of natural rubber blends and IPNs. The time and... 

Pi om a mesoscopic point of view, when a semicrystalline polymer is submitted to a large deformation, the spherulitic structure is gradually broken down, while increasing moleculai orientation. In a tensile deformation, the spherulitic could be reformed ultimately in a new oriented microstructure the oriented fibrillar texture [190]. Such cold processed polymer fibers may have a Young s modulus, which could nearly reach 150 GPa for polyaramid fibers (Kevlar ). The strong link between microstructme and mechanical properties can be easily predicted. 

Numerical methods with different time- and length scales are employed and developed to investigate material properties and behaviors. Among them, molecular modeling can predict the molecular behaviors and correlate macroscopic properties of a material with various variables. The most popular techniques include molecular mechanics (MM), MD, and Monte Carlo (MC) simulation. These techniques are now routinely used to investigate the structure, dynamics, and thermodynamics of inorganic, biological, and polymer systems. They have recently been used to predict the thermodynamic and kinetic properties of nanoparticle-matrix mixtures, interfacial molecular structure and interactions, molecular dynamic properties, and mechanical properties. 

---