Amorphous and semicrystalline thermoplastic

A truncation of the term thermoplastics. Generally organic materials which in the manufacturing stage are caused to flow by the application of heat and pressure and thus take up a desired shape, which shape is retained when the applied heat and pressure are removed. Plastics are high polymers and are classified into amorphous and semicrystalline thermoplastics and thermosetting materials. 

Materials Studied. The materials investigated are listed in Table I. Different amorphous and semicrystalline thermoplastics were used as matrix materials, which were modified with several types of rubber. The volume content of the rubber and the rubber-particle diameter were changed to enable A... 

Figures 2 and 3 illustrate the quantitative influence of molar mass M on a number of technical and physical properties of amorphous and semicrystalline thermoplastics.

The primary forming of amorphous and semicrystalline thermoplastics is reahzed in the flow or melting range. Figure 10 shows mice again that the individual states have no fixed temperature limits. The temperature-dependence of the processability of thermoplastics is shown clearly. 

This difference in the deformation characteristics of amorphous and semicrystalline thermoplastics can be attributed to their different molecular structures. As already mentioned, the intermolecular forces operate with much greater strength in the crystalline than in the amorphous state. 

Fig. 22. Representative static plane-strain toughness values of different amorphous and semicrystalline thermoplastics as a function of the square root of the entanglement density. From Refs. 26 and 27.

Mechanical properties compare favorably with other high performance amorphous and semicrystalline thermoplastics, where strength and toughness requirements are rigorous (Table 1). The flexural recovery (resilience) of polyarylate is excellent over a wide temperature range, which suggests applications where snap-fit action is required. 

As already discussed in section 1.4, we distinguish amorphous and semicrystalline thermoplastics, elastomers and duromers. All explanations given in the following relate to amorphous thermoplastics, unless noted otherwise. The peculiarities of the other groups are discussed separately. 

Ultrasonic welding is used to assemble amorphous and semicrystalline thermoplastic components that have joints that are butt, lap, tongue and groove, and shear. The typical ultrasonic normal vibration in the range of 15-70 kHz and 10-50 pm oscillates two mating components to create the weld. The amplitude of vibration generates the heat required to melt and flow the joint and is thus polymer dependent. Ultrasonic... 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

The time needed for polymer chains of amorphous thermoplastics above Tg and semicrystalline thermoplastics above Tm to diffuse across the interface and randomize is relatively short compared with the time needed for resin flow. It is believed, therefore, that diffusion bonding is completed immediately after the two molten surfaces merge, and that the microstructure of the contact zone is also assumed to be identical to that of the intraply sections [12,13],... 

The model PBZT/ABPBI molecular composite system is limited since the rod and the matrix do not possess glass transition temperatures for subsequent post form consolidation. In an effort to improve the processability for molecular composites, thermoplastics were used as the host matrix. Processing from acidic solvents requires the thermoplastic host to be soluble and stable in meth-anesulfonic add. Thermoplastic matrices were investigated including both amorphous and semicrystalline nylons [71,72], polyphenylquinoxaline (PPQ) [73] and polyetheretherketone (PEEK) [74], Table 5 shows the mechanical properties obtained for various processed PBZT thermoplastic molecular composite systems. As an example, the PBZT/Nylon systems showed 50-300% improvement over uniaxially aligned chopped fiber composite of comparable compositions. However, the thermally-induced phase separation during consol-... 

The two methods of improving the macroscopic toughness of thermosets are similar to those used for amorphous or semicrystalline thermoplastics (i) plasticization and (ii) amplification of deformation mechanisms via the generation of a heterogeneous structure. 

In thermoplastic matrices, the intrinsic characteristics derived from the linear chain structure have to be considered, mainly the capability of flow under stress at high temperatures. Thus, in amorphous and semicrystalline matrices, the service temperatures will be determined by Tg or Tg and T, respectively. Without reinforcement, creep is a major problem at temperatures lying in the interval Tg < T < r , but when the matrices are... 

Novel Composites from Blends of Amorphous and Semicrystalline Engineering Thermoplastics with Liquid-Crystalline Polymers... 

The aim of this work is to study the influence of particle size, interparticle distance, particle volume content, and local stress state on the toughening mechanism in several dispersed systems. The systems consist of a matrix of an amorphous or semicrystalline thermoplastic (see Figure 1). It is necessary to determine whether the particle diameter or the interparticle distance is of primary importance. But it is difficult to check the influence of both parameters because there is an interrelation between D, the average minimum value of A, and the particle volume content, t>P ... 

The two principal types of polymerization for thermoplastics including engineering thermoplastics are polycondensation polymerization and chain-growth polymerization. Both types can usually produce hnear, branched, crosslinked amorphous and semicrystalline aromatic and aliphatic polymers [14]. 

Thermomechanical behaviour is most probably the most widely exploited property of engineering thermoplastics. Figure 3.1 shows the behaviour of two types of thermoplastic, one amorphous and the other semicrystalline, versus temperature. We can see several steps moving from low to high temperatures ... 

Figure 3.1. Examples of modulus variations versus temperature for an amorphous and a semicrystalline thermoplastic...

The phenomenological ordering of polymers projected for use as constructing materials is not an easy matter. Sometimes the temperature stability is used as a criterion, i.e., the temperature up to which the mechanical properties remain more or less constant. Another attempt for classification, uses the E modulus or the shape of the curve of stress-strain measurements (see Sect. 2.3.5.1). In general one can say that semicrystalline thermoplastics are stiff, tough, and impact-resistant while amorphous thermoplastics tend to be brittle. Their E... 

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