Mechanical behavior, dynamic

17 complements this model with experimental data which show changes in tan5 peak positions associated with tightly and loosely bound polymer. The second tan 5 peak changes when a loosely bound polymer transits to a tightly bound polymer.  

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Transitions. Samples containing 50 mol % tetrafluoroethylene with ca 92% alternation were quenched in ice water or cooled slowly from the melt to minimise or maximize crystallinity, respectively (19). Internal motions were studied by dynamic mechanical and dielectric measurements, and by nuclear magnetic resonance. The dynamic mechanical behavior showed that the CC relaxation occurs at 110°C in the quenched sample in the slowly cooled sample it is shifted to 135°C. The P relaxation appears near —25°C. The y relaxation at — 120°C in the quenched sample is reduced in peak height in the slowly cooled sample and shifted to a slightly higher temperature. The CC and y relaxations reflect motions in the amorphous regions, whereas the P relaxation occurs in the crystalline regions. The y relaxation at — 120°C in dynamic mechanical measurements at 1 H2 appears at —35°C in dielectric measurements at 10 H2. The temperature of the CC relaxation varies from 145°C at 100 H2 to 170°C at 10 H2. In the mechanical measurement, it is 110°C. There is no evidence for relaxation in the dielectric data. 

Curran, D.R., Dynamic Mechanical Behavior of Iron Solids (edited by Burke, J.J. and Weiss, V.), Syracuse University Press, Syracuse, 1971, pp. 121-138. 

Although the liquid crystalline phase of most polybibenzoates usually undergoes a rapid transformation into a three-dimensional crystal, the introduction of oxygen atoms in the spacer of polybibenzoates has been used to prevent or to slow down this transformation. The dynamic mechanical behavior of polybibenzoates with 2, 3, or 4 oxyethylene groups in the spacer (PDEB, PTEB, and PTTB, respectively) is determined by the composition of the spacer [24], as discussed in this section. 

Adicoff, Dynamic Mechanical Behavior of Highly Filled Polymers Dewetting Effect , Rept No NWC-TP-5486 (1971) 11) H. Yasu-... 

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

Figure 3. Dynamic mechanical behavior of PMMA-g-PSX copolymer 20 wt.% siloxane of M 10,000.

Recent work has focused on a variety of thermoplastic elastomers and modified thermoplastic polyimides based on the aminopropyl end functionality present in suitably equilibrated polydimethylsiloxanes. Characteristic of these are the urea linked materials described in references 22-25. The chemistry is summarized in Scheme 7. A characteristic stress-strain curve and dynamic mechanical behavior for the urea linked systems in provided in Figures 3 and 4. It was of interest to note that the ultimate properties of the soluble, processible, urea linked copolymers were equivalent to some of the best silica reinforced, chemically crosslinked, silicone rubber... 

Figure 4. Dynamic mechanical behavior of siloxane-urea copolymers prepared from H-MDI. Curve A PSX-1 50-HMDI-81 curve B PSX-1770-HMDI-8 curve C PSX-770-HMDI-91 curve D PSX-3680-HMDI-94. (Reproduced with permission from Ref. 25. Copyright 198 1 IPC Business Press, Ltd.)...

Figure 7. Effect of TEOS content on the dynamic mechanical behavior of TEOS-PTMO materials (PTMO MW=2000), (a) storage modulus and (b) tanS.

The dynamic mechanical behavior of the block copolymers of HB and HI are typified by the results obtained for the HIBI series which are given in Figure 15A and B which display spectra for different composition ratios. The transition behavior of the HBIB series is so similar that it will not be repeated here. The samples used for this study were compression molded and they all had been stored at room temperature between one to two months before use. The experiments were run at 110 Hz. The behavior of HB, represented by HIBI 100, is similar to that given in Figure 14B. 

The dynamic mechanical behavior indicates that the glass transition of the rubbery block is basically independent of the butadiene content. Moreover, the melting temperature of the semicrystalline HB block does not show any dependence on composition or architecture of the block copolymer. The above findings combined with the observation of the linear additivity of density and heat of fusion of the block copolymers as a function of composition support the fact that there is a good phase separation of the HI and HB amorphous phases in the solid state of these block copolymers. Future investigations will focus attention on characterizing the melt state of these systems to note if homogeneity exists above Tm. 

The dynamic mechanical behavior of most homogeneous and heterogeneous solid and molten polymeric systems or composite formulations can be determined by DMA. These polymeric systems may contain chemical additives, including fillers, reinforcements, stabilizers, plasticizers, flame retardants, impact modifiers, processing aids, and other chemical additives, which are added to the polymeric system to impart specific functional properties and which could affect the process-ability and performance. 

The DMA of rubber-based nanocomposites has been the subject of recent research. Many literature reports describe the dynamic mechanical behavior of rubber-based nanocomposites [155, 156]. Das et al. have studied the DMA of CR nanocomposites based on montmorillonite clay and LDH [157]. The montmorillonite clay is... 

Kotaka,T., Osaki,K. Normal stresses, non-Newtonian flow, and dynamic mechanical behavior of polymer solutions. J. Polymer ScL Pt.C 15,453-479 (1966). 

Summary In this chapter, a discussion of the viscoelastic properties of selected polymeric materials is performed. The basic concepts of viscoelasticity, dealing with the fact that polymers above glass-transition temperature exhibit high entropic elasticity, are described at beginner level. The analysis of stress-strain for some polymeric materials is shortly described. Dielectric and dynamic mechanical behavior of aliphatic, cyclic saturated and aromatic substituted poly(methacrylate)s is well explained. An interesting approach of the relaxational processes is presented under the experience of the authors in these polymeric systems. The viscoelastic behavior of poly(itaconate)s with mono- and disubstitutions and the effect of the substituents and the functional groups is extensively discussed. The behavior of viscoelastic behavior of different poly(thiocarbonate)s is also analyzed. 

Keywords Viscoelasticity Glass transition temperature Relaxational processes Dielectric behavior Dynamic mechanical behavior Poly(methacrylate)s Poly (itaconate)s Poly(thiocarbonate)s Spacer groups Side chains Molecular motions... 

Fig. 6 Dynamic mechanical behavior for different film species of a cellulose composite synthesized with a monomer mixture of VP/GMA = 3/7, representing an effect of the chemical treatment of an original sample (CELL/P(VP-co-GMA)[0]) with aqueous formic acid [F] or sodium hydroxide [S] solution. CELL content = 4.5 wt%. (Reproduced from [73])...

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