Viscoelastic measurements dynamic

PMMA-b-PBA shows improved izod impact strength compared to PMMA homopolymer (41). Polyisobutylene (PIB) or its hydrogenated one (PIB-H) also acts as an impact modifier [31]. PSt-b-PIB, PSt-b-PIB-H, and PMMA-b-PIB-H derived from MAI have high- and wide-range molecuiar weight and show high flexibiiity and flow property [42]. The improved flexibiiity of PMMA-b-PEG synthesized as an elastomer, was confirmed by dynamic viscoelastic measurement [43]. 

The specimen was prepared by the following method. After mixing HAF carbon black (50 phr) with natural rubber (NR) in a laboratory mixer, carbon gel was extracted from unvulcanized mixture as an insoluble material for toluene for 48 h at room temperamre and dried in a vacuum oven for 24 h at 70°C. We made the specimen as a thin sheet of the carbon gel (including carbon black) by pressing the extracted carbon gel at 90°C. The cured specimen was given by adding sulfur (1.5 phr) to the unvulcanized mixture and vulcanized for 30 min at 145°C. The dynamic viscoelastic measurement was performed with Rheometer under the condition of 0.1% strain and 15 Hz over temperatures. 

Fig. 4 Dynamic viscoelasticity measurements after equal mixing of 5 wt%...

The static modulus and dynamic storage modulus were investigated for some open-celled PE foams by static compression tests and dynamic viscoelastic measurements in compression mode. Experimental data were compared with theoretical predictions. 8 refs. 

The dynamic storage modulus of closed-cell PE foams was investigated by dynamic viscoelastic measurement in the compression mode. It was found that dynamic modulus correlated with compression hardness and that the resistance against pressure inside the cells had no effect upon static modulus or dynamic storage modulus. 8 refs. 

Figure 19 shows dynamic shear modules (G ) and loss tangent (tan 8) as a functions of temperature for carboxymethylated wood binding various metal ions [49]. The content of carboxymethyl groups in treated wood is about 1.07 mmol/g for each specimen. Dynamic viscoelastic measurements were carried out under vacuum. There are three dispersions in the range below 1(X)°C the P dispersion near 50°C for the carboxymethylcellulose main chain motion in the modified wood, the 7 diversion near 0°C for local mode of wood components related to water, and the 8 dispersion near - 60°C for the side chain... 

An empirical equation was used to predict the peak loss factor temperature of dynamic viscoelastic measurements from DSC T data. The frequency for DSC T was given an arbttuary value of 10 Hz. 

The E value determined by dynamic viscoelasticity measurements is 2 x 1011 dyne/ cm3 at room temperature. It decreases abruptly in the temperature range 140-150°C, but the net decrease of E within this temperature range is relatively small. 

Photophysical and photochemical processes in polymer solids are extremely important in that they relate directly to the functions of photoresists and other molecular functional devices. These processes are influenced significantly by the molecular structure of the polymer matrix and its motion. As already discussed in Section 2.1.3, the reactivity of functional groups in polymer solids changes markedly at the glass transition temperature (Tg) of the matrix. Their reactivity is also affected by the / transition temperature, Tp, which corresponds to the relaxation of local motion modes of the main chain and by Ty, the temperature corresponding to the onset of side chain rotation. These transition temperatures can be detected also by other experimental techniques, such as dynamic viscoelasticity measurements, dielectric dispersion, and NMR spectroscopy. The values obtained depend on the frequency of the measurement. Since photochemical and photophysical parameters are measures of the motion of a polymer chain, they provide means to estimate experimentally the values of Tp and Tr. In homogeneous solids, reactions are related to the free volume distribution. This important theoretical parameter can be discussed on the basis of photophysical processes. 

Reinforced vulcanized samples generally present a marked viscoelastic behavior that is usually studied by dynamic viscoelastic measurements. In this experiment, a sample is subjected to periodic sinusoidal shear strain y... 

Fig. 25 Results of dynamic viscoelastic measurements of PPCN and PO1015 (a) storage modulus (b) relative storage modulus of PPCN to PO1015...

Endo et al. reported a synthesis ofpoly(l,2-dithiane) (PDT) [151,152] that possibly contained polycatenane structures (Scheme 17.24). A melt polymerization [153] of 1,2-dithiane 84, without initiators, yielded the polymer 85, the NMR analysis of which confirmed the presence of large cyclic structures, which were further verified using by mass spectroscopy and photodegradation analysis. In addition, dynamic viscoelastic measurements showed that the molten state of the polymer 85 has a rabbery plateau, while the Tg of PDT decreased with increasing molecular weight. These observations, which differed from those obtained with the linear PDT analog, provided further evidence for the formation of polycatenane structures. In taking... 

Small-Strain Properties, Dynamic Viscoelastic Measurements... 

Reinforced vulcanized samples generally present a marked viscoelastic behavior that is usually studied by dynamic viscoelastic measurements. In this experiment, a sample is subjected to periodic sinusoidal shear strain y (at defined frequency (o and temperature T). Its dynamic shear modulus G is complex and can be written as the sum of the storage modulus G, and the loss modulus G". 

At large strain, dynamic viscoelastic measurements can not be made accurately because of the important self-heating of the sample during the experiment. Therefore large-strain properties are usually determined by uniaxial extension [144] (Fig. 6). 

Carbon black or silica filled NR generally demonstrates viscoelastic behaviour that is usually evaluated by dynamic viscoelastic measurements. One of the most widely discussed in the literature is the strain dependency of dynamic modulus known as the Payne effect. In such cases a high dynamic modulus at low strains (< 1%) is measured, which decreases at higher strains (> 10%), as shown in Figure 24.1. The reason for this phenomenon is the formation of a network created by filler-filler interactions. For carbon black the interactions are Van der Waals forces and for silica, much stronger hydrogen... 

Dynamic viscoelastic measurements can be made at very low concentrations and extrapolated to infinite dilution to obtain intrinsic stor e and loss moduli, [O ] and [G"] of the isolated polymer chain. Measurements have been made on a nine-branch star polystyrene and a four-branch star polybutadiene in several solvents including two 8 solvents in the former case and over a frequency range of about 100 to 6000 At low frequency [G"] will be in error since [t ] (= [G"]/cui s)u o is... 

In this chapter, we outline the principle, measurement, and application of dynamic viscoelasticity for solid and liquid polymers. In Section II, a basic treatment of the dynamic viscoelasticity is described. Section III deals with the various dynamic viscoelastic measurements of solid and liquid polymers. Section IV reviews in detail the results of linear dynamic viscoelasticity as a function of frequency and temperature. The dynamic mechanical studies have... 

Dynamic viscoelastic measurements are useful in studying the structure of polymers, because these mechanical properties are sensitive to glass transition, crystallinity, cross-linking, filling systems (filler or plasticizer), molecular aggregation, and phase separation. To determine dynamic viscoelastic properties, such as storage modulus, loss modulus, and tan, various methods have been proposed, and recently many types of instruments are commercially available. Typical methods to measure the dynamic viscoelasticity are classified into three categories damped free vibration, resonance free vibration, and nonresonance forced vibration. These methods are standardized by the international standard ISO 6721 [3]. 

For both scientific and commercial purposes, the dynamic viscoelastic measurement as a function of temperature is now the important technique to characterize polymer materials. The temperature dependence of the dynamic viscoelastic parameters, especially tan S, is sensitive to the molecular motion, structure, and morphology of the polymer. 

Fig. 38 A moisture control system for dynamic viscoelastic measurements as a function of relative humidity. (From Ref. 41.)...

It is well known that filler-filled systems have very complex rheological properties and structures which vary in different flow fields and show special phenomena accompanied by structural changes. The processability of these dispersed systems is determined not only by their viscosities but also by their elasticities. In order to clarify the nature and the reformation process of their internal structure, dynamic viscoelasticity measurements were carried out extensively [6-8,47-51,53]. For systems filled with solid particles, the viscoelastic properties especially the dynamic ones as well as the steady flow properties have been studied extensively, and it has been found that the rheological properties of the dispersed systems differ from those of polymer solutions and melts in several ways. 

Extensive dynamic viscoelastic measurements on polyvinyl chloride gels with well-defined tacticities and thermal histories have revealed changes in aging which affect the plateau zone as some crystallites melt and others are formed. The appearance of secondary loss mechanisms is attributed to the formation of entan-gelments during the aging process. 

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