The Effect of Crystallinity on Mechanical Properties

The miscibility of olefin copolymers such as ethylene-a-olefin copolymers was found to be controlled by the structural composition and the primary strucmre of the copolymers. Using these copolymers, binary blends with various compatibilities were prepared and the effects of compatibihty on mechanical properties in the binary blends were investigated. The tensile properties in binary blends of iPP with rubbery olefin copolymers are considerably influenced by the miscibility between iPP and the copolymers. The miscibility of iPP with other polyolefins is described in detail based on the dynamic mechanical properties, morphology observation, and solidification process. It is found that EBR, EHR, and EOR having more than 50 mol% of a-olefin are miscible with iPP in the molten state. In the solid state, the miscible copolymers are dissolved in the amorphous region of iPP, although the copolymers are excluded from crystalhne lattice of iPP. The isotactic propylene sequence in the EP copolymers with a propylene-unit content of more than 84 mol% participates in the crystallization process of iPP, resulting that a part of the EP copolymers is included in the crystalline lattice of iPP. 

To illustrate the effect of temperature on mechanical properties, it is sometimes preferable to plot the property vs. temperature for constant values of time. For example, data of the type shown in Fig. 18.21 may be cross-plotted as (10) (the 10-second relaxation modulus) vs. T, Such a plot is given in Fig. 18.23 for several polystyrene samples," The five regions of viscoelastic behavior are evident in the linear, amorphous (atactic) samples (A) and (C) along with the effect of molecular weight in the flow region. The drop in modulus in the vicinity of Tg (100°C) is dearly seen. The crystalline (isotactic) sample maintains a fairly high modulus all the way up to (a 235 "C). Given values of one can convert data in the form vs, t at constant T (a master curve) to vs. T at constant t and vice versa. 

With this correlation of the hardness test established, efforts were then directed toward the determination of the effect of crystallinity on the mechanical properties of the fluoroplastics at cryogenic temperatures. 

Following the approach of Diez-Gutierrez et al. [53] that studied the effect of filler on the mechanical properties of talc/polypropylene composites, Fambri et al. [54] analyzed the effect of crystallinity on the storage modulus E of PLLA through a glass transition intensity factor defined as... 

A major topic of interest relating to film structure is the effect of crystallinity on the deformation mechanism. The optical properties of biaxially oriented films were studied in 1957 by Stein [109] who determined the full set ofbirefrin-gences, by measuring the optical retardation as a function of the tilt of a PS film. Samuels [110] used complementary techniques of x-ray scattering, TEM of surface replicas and birefringence measurement in a study of the microstructure... 

The fringed micelle model has been superseded as new information has led to the development of more advanced models. Nevertheless, it still does a good job of qualitatively predicting the effects of crystallinity on the mechanical properties of the polymers. 

The greater the degree of crystallinity the less the water absorption and hence the less will be the effect of humidity on the properties of the polymer. The degree of crystallinity also has an effect on electrical and mechanical properties. In particular high crystallinity leads to high abrasion resistance. 

Effects of Crystallinity on Properties. In polymers that can crystallize, the ratio of crystalline to amorphous material has a profound effect on properties. Because the chains arc packed more tightly and efficiently in the crystalline areas Ilian in the amorphous, the cryslalline phase lias a higher density and greater mechanical strength. In fact, density is a common measure of degree of crystallinity,... 

Historically most of the microscopic diffusion models were formulated for amorphous polymer structures and are based on concepts derived from diffusion in simple liquids. The amorphous polymers can often be regarded with good approximation as homogeneous and isotropic structures. The crystalline regions of the polymers are considered as impenetrable obstacles in the path of the diffusion process and sources of heterogeneous properties for the penetrant polymer system. The effect of crystallites on the mechanism of substance transport and diffusion in a semicrystalline polymer has often been analysed from the point of view of barrier property enhancement in polymer films (35,36). 

Qayyum, M.M. White, J.R. The effect of weathering on residual stresses and mechanical properties in injection-moulded semi-crystalline polymers. J. Mater. Sci. 1986, 21, 2391-2402. 

It was previously shown that rapidly solidified Al-RE and Al-TM-RE alloys (RE is rare earth metal or yttrium, TM is transition metal) have amorphous structure in relatively wide range of compositions and alloying elements [1], Similarly to rare earth metals and Y, Sc belongs to the IIIB group of the Periodic Table of Elements, but we have found no data on the influence of Sc on the formation of amorphous structure in A1 alloys in the literature. On the other hand, Sc is known for a many-sided improving action on many crystalline A1 alloys [2], The aim of this work was to investigate the effect of Sc on the structure and mechanical properties (hardness) of rapidly solidified binary Al-Sc alloys as well as of Al-Ce-Sc and Al-Ni-Ce-Sc amorphous alloys. 

All mechanical properties depend on crystallinity, orientation and crosslinking. These three factors will all be discussed in this chapter. See also Kinloch and Young [2] and van Krevclcn [71 for discussions on the effects of crystallinity and orientation on the mechanical properties. The discussion of the morphologies and the mechanical properties of multiphase polymeric systems (such as composites and blends) will be postponed to Chapter 19 and Chapter 20, respectively, where crystallinity and orientation will be discussed further in this broad context. 

Next, an attempt was made to clarify the effect of crystalline phase on the mechanical properties of ethylene ionomer. Dynamic mechanical measurements... 

In partly crystalline polymers, it is important to treat separately the effect of irradiation on the mechanical properties above and below the crystalline melting point. Induced crosslinks indeed determine the mechanical properties above the melting point whereas crosslinks and crystallinity must both be taken into account below the melting point. 

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