Rubber demonstrations

The levulinic aldehyde and acid obtained by Harries on hydrolyzing the ozonide of rubber demonstrated recurrence of the structure... 

Additional testing in natural rubber demonstrated that particle size was significant in Firestone running temperature, as was structure (Fig. 20). Smaller particle size and higher structure both increase heat build-up. 

In the first experiments, the crack behavior for uniform rubber material was measured (Fig. 16.7(a)). As the force F applied to the crack increased, so did the crack speed. Identical behavior was observed for different rubber thicknesses and also for the stiffened rubber, demonstrating the simplicity of the peel crack system in which the peel force F depends only on the adhesive fracture energy R at a given crack speed, as shown by the peel equation (Chapters 7 and 13). 

First extruder experiments on EPDM rubber demonstrate that standard equipment can easily be modified for SFE (40). For successful extractions an extraction time of 2 minutes is not long enough. 

Figure 3.2 shows a Raman spectrum of nitrile rubber demonstrating the sensitivity of the C=C stretching vibration to its environment in the polymer molecule. 

Ghosh and co-workers [6] in their study of the electrical properties of sulfonated maleated ethylene propylene diene rubber, demonstrated the occurrence of a characteristic frequency dependent on the high temperature peak (83-124 °C) which was ascribed to two different types of dielectric relaxations associated with multiplets... 

There is considerable evidence that all the hysteresis effects observed in these materials and most of the viscoelastic behavior can be caused by the time dependent failure of the polymer on a molecular basis and are not due to internal viscosity [1,2]. At near equilibrium rates and small strains filled polymers exhibit the same type of hysteresis that many lowly filled, highly cross-linked rubbers demonstrate at large strains [1-8]. This phenomenon is called the "Mullins Effect" and has been attributed to micro-structural failure. Mullins postulated that a breakdown of particle-particle association and possibly also particle-polymer breakdown could account for the effect [3-5]. Later Bueche [7,8] proposed a molecular model for the Mullins Effect based on the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the composite. Such deformations would cause a highly non-uniform strain and stress gradient in the polymer... 

Some 500 years ago during Columbuss second voyage to what are now the Americas he and his crew saw children playing with balls made from the latex of trees that grew there Later Joseph Priest ley called this material rubber to describe its ability to erase pencil marks by rubbing and in 1823 Charles Macintosh demonstrated how rubber could be used to make waterproof coats and shoes Shortly there after Michael Faraday determined an empirical for mula of CsHs for rubber It was eventually determined that rubber is a polymer of 2 methyl 1 3 butadiene... 

L First manufacturing use of chemically amplified resists Plasma-developed resist first described X-ray proximity lithography demonstrated Bis-azide rubber resists introduced DNO-novolac resist for microelectronics introduced Photoresist technology first applied to transistor fabrication DNO-novolac resist patented by Kalle... 

Initially, all of the SBR polymer known as GR-S produced during World War II was by the batch process. Later, it was thought that a higher volume of polymer would be needed for the war effort. The answer was found in switching from batchwise to continuous production. This was demonstrated in 1944 at the Houston, Texas, synthetic mbber plant operated by The Goodyear Tire Rubber Company. One line, consisting of 12 reactors, was lined up in a continuous mode, producing GR-S that was mote consistent than the batch-produced polymer (25). In addition to increased productivity, improved operation of the recovery of monomers resulted because of increased (20%) reactor capacity as well as consistent operation instead of up and down, as by batchwise polymerisation. 

A somewhat similar thing happens in many polymers at the glass-rubber transition that we mentioned in Chapter 6. Below the transition these polymers are much more brittle than above it, as you can easily demonstrate by cooling a piece of rubber or polyethylene in liquid nitrogen. (Many other polymers, like epoxy resins, have low Gc values at all temperatures simply because they are heavily cross-linked at all temperatures by covalent bonds and the material does not flow at the crack tip to cause blunting.)... 

Demonstrations (a) Balloons and safety pin (see Chapter 13, p. 121). Afterwards, put fractured edges of balloon rubber on overhead to show that wavy fracture path closely parallels that seen when metals have undergone fast fracture, (b) for Sellotape (see Chapter 13, p. 122). 

It has been demonstrated that with SBR polystyrene blends the rubber should exist in discrete droplets, less than 50 p.m in diameter where a good finish is required, within the polystyrene matrix. It is believed that in such a form the rubber can reduce crack propagation and hence fracture in various ways. The most favoured current explanations of this were discussed in Chapter 3. Suffice it to say here that the following features appear necessary for a suitable blend ... 

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Class and Chu demonstrated that if a tackifier is chosen that is largely incompatible with the elastomer, a modulus increase due to the filler effect is observed and little change in Ta results, and once again a PSA would not be obtained. This was observed for mixtures of low molecular weight polystyrene resin and natural rubber. The same polystyrene resin did tackify SBR, a more polar elastomer that is compatible with the resin. Hydrogenating the polystyrene to the cycloaliphatic polyvinylcyclohexane changed the resin to one now compatible with the less polar natural rubber and no longer compatible with SBR. These authors also provide... 

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

Free radicals are initially generated whenever polymer chains are broken and carbon radicals are formed. These effects occur during manufacture and in service life. Many elastomers are observed to oxidize at relatively low temperature (about 60°C), where carbon-hydrogen and carbon-carbon bond cleavages are highly unlikely. It has been demonstrated [52] that traces of peroxides impurities in the rubber cause low-temperature oxidation of rubber. These initiating peroxides are present in even the most carefully prepared raw rubber polymer [53]. 

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

The data also demonstrate that the addition of the thermoplastic, PMMA, does not have the significant effect on the toughness or adhesion properties as does the addition of the rubber, Vamac B-124. Clearly, the physical properties of the polymeric additive determine the magnitude of the adhesive physical property modifications, which result from their addition to an alkyl cyanoacrylate monomer. 

In all the compositions, the DCP-cured blends showed better properties than the corresponding unvulcanized samples. Choudhary et al. [30] further demonstrated the use of EPDM, chlorinated PE, chlorosulfo-nated PE, maleic anhydride modified polyethylene, and blends of epoxidized natural rubber-sulfonated EPDM as compatibilizers in NR-LDPE (low-density PE) blends. 

A small forerun of 2,4-pentanedione, b p 32-100° (19 mm.), is obtained The purity of the product may be demonstrated by gas chromatography on a 2-ft column packed with silicone gum rubber (F and M Scientific Co, Avondale, Pennsylvania) programmed linearly from 100° to 300° The chromatogram obtained is a single sharp peak The three conceivable impurities, 2,4-pentanedione, 3-butyl 2,4-pentanedione, and 6,8-tridecanedione, would have been observed under these conditions if they had been present. 

There is an interesting demonstration experiment that you can do with a rubber band, preferably a large and/or thick one. Touch the unstretched rubber band to your lips. Then, stretch the rubber band... 

In reality the ideal elastic rubber does not exist. Real rubbery materials do have a small element of viscosity about their mechanical behaviour, even though their behaviour is dominated by the elastic element. Even so, real rubbers only demonstrate essentially elastic behaviour, i.e. instantaneous strain proportional to the applied stress, at small strains. 

Different characteristics of solvents seriously affect the sol-gel reaction in solution. This in turn influences the physico-mechanical properties of the resultant rubber-silica hybrid composites. Bandyopadhyay et al. [34,35] have carried out extensive research on stmcture-property correlation in sol-gel-derived rubber-sihca hybrid nanocomposites in different solvents with both chemically interactive (ENR) and noninteractive (ACM) mbber matrices. Figure 3.12 demonstrates the morphology of representative ACM-sihca and ENR-sihca hybrid composites prepared from various solvents. In all the instances, the concentration of TEOS (45 wt%), TEOS/H2O mole ratio (1 2), pH (1.5), and the gelling temperature (ambient condition) were kept unchanged. 

Our work with SDIBS demonstrated that TPEs based on amorphous plastic-rubber-plastic blocks do not necessarily require narrow MWD for good phase separation and mechanical properties some of these SDIBS blocks exhibited MWD >2, and irregular phase morphology. This disagrees with earlier conventional wisdom and opens new avenues in TPE research. 

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