Copolymer elastic modulus

Curve El in Fig. 2.21 corresponds to an elastomer (statistic copolymer from ethylene and propylene), characterized by a low value of the elastic modulus... 

Fig. 2.22. Dependence of the elastic modulus E and the mechanical loss factor 6 on temperature for various polymers. Curves 1 elastomer (statistical copolymer of ethylene and propylene) curves 2 isotactic polypropylene (semicrystalline)...

Improvement of the mechanical properties of elastomers is usually reached by their reinforcement with fillers. Traditionally, carbon black, silica, metal oxides, some salts and rigid polymers are used. The elastic modulus, tensile strength, and swelling resistence are well increased by such reinforcement. A new approach is based on block copolymerization yielding thermoelastoplastics, i.e. block copolymers with soft (rubbery) and hard (plastic) blocks. The mutual feature of filled rubbers and the thermoelastoplastics is their heterogeneous structure u0). 

Fig. 9 Master curves obtained while heating (empty symbols) and cooling (full symbols) the material created by the association of a,co-3,5-dinitrobenzoate PDMS with the PCzEMA-h-PDMS-fi-PCzEMA triblock copolymer. Reference temperature 25°C, ( ) elastic modulus G , ( ) viscous modulus G ...

Of course the modulus of a block copolymer with ordered spherical microdomains is much lower than that of a crystalline solid. Near the disordering transition, the potential energy holding each domain or atom in place is of order ksT, and the modulus is roughly vksT, where v is the number of domains or atoms. This gives an elastic modulus 10 -10 dyn/cm for typical block copolymers with spherical domains, as opposed to 10 -10 dyn/cm for atomic crystals. Ordered spherical diblock copolymers are therefore soft solids. They deflect under an imposed shear stress, but do not flow continuously unless that stress exceeds a critical value, the yield stress (Watanabe and Kotaka 1984). 

Fig. 6. Tapping Mode (left) versus force modulation mode (right) picture with the corresponding height and elasticity modulus profiles of a solution-cast 20wt% silicone thin copolymer film.

Figure l visualizes the influence of overall chain rigidity produced by variation of the PHB-content x in the copolymer on the elastic modulus parallel and transverse to the applied injection flow. 

Figure 1. Elastic modulus of PET/xPHB copolymers in function of x determined in the direction parallel ( ) and transverse to the flow ( ).

Figure 51. Dependence of shear elastic modulus on the volume concentration of block copolymers of styrene and butadiene (filled circles) [140], The solid line represents the calculation results.

Elongation of PVC as a function of dose and temperature has been performed by Chapiro [432]. Minor changes are observed after irradiation in vacuo (Fig. 46). After a 41 Mrad dose, however, the polymer does not flow even at 250°C since a three-dimensional network was formed. Irradiation in air reduces the temperature of breaking even at low doses. A stress—strain curve for PVC is reported by Busch [433]. An important reduction in tensile strength is observed. Neutron-irradiated PVC, vinyl chloride—vinylidene chloride copolymers and vinyl acetate—vinyl chloride copolymers were compared. Reduction in tensile strength and elastic modulus was observed for the first copolymer whereas the second showed considerable increase in the elongation at break [434]. 

Addition of glass fibers, for example, is found [57] to yield products with very high stifl iess (e.g., elastic modulus E == 2800 MPa with 30% glass fiber), higher than that with talc (E = 1250 MPa with 20% talc) and far better than that of the original mixture (E=950 MPa). Addition of LDPE and styrene-butadiene-styrene copolymer, on the other hand, improves the tenacity (showing, typically, a 30-90%... 

Jung et al. have developed a synthetic elastomer composed of acrylonitrile butadiene rubber copolymer [211, 212]. The properties of the copolymer can be tuned by changing its composition. Reported data for dielectric constant, elastic modulus, and strain relaxation are promising (see Table 1.2). The synthetic elastomer provides some improvement over VHB and some silicone hlms under certain conditions however, the tests were limited to low prestrain (60% radial), where the performance of VHB hlms is poor. 

Fig. 4.5 Atomic force microscopy (AFM) phase image of the top surface of a thin film of poly (styrene)-h-poly(oxyethylene) diblock copolymer presenting a phase of hexagonally packed cylinders aligned perpendicular to the substrate after annealing in benzene vapor. The image contrast comes from the difference of elastic modulus between the domains. Adapted with permission from ref. [62], Adv. Mater. 2004,16, 226. Copyright 2004 John Wiley and Sons...

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