Rigidity with Composition

Foamed plastics can be classified in different ways, for instance by their nature (flexible vs. rigid), chemical composition of the matrix, density, cell size, cell structure (open-celled vs. closed-celled), processing method, and dimensions. It is the aimed combination of these properties that determines the final application of the cellular polymer. As an example, open-celled ultra-low density foams are highly desirable for acoustical insulation, while rigid foams with closed-cells and elevated densities are preferred as load-carrying core materials in composite materials. 

DaunoXome liposomes are also long circulating liposomes, in this case encapsulating the cytostatic daunorubicin. Although a non-stealth system, long circulation times are attained by using a particularly rigid bilayer composition, in combination with a relatively small liposome size. 

Figure 34. Comparison of the flexural strengths of unidirectional carbon/carbon composites (left-hand side) with those of hybrid composites in which the final impregnation is made with an epoxy resin (34) The composites were fabricated with high-modulus fibers rigidized with phenolic resin, and subjected to four densification cycles with coal-tar pitch plus sulfur.

Figure 35. Mechanical properties of carbon/carbon epoxy-resin hybrid composites, compared with the properties of the composite skeletons before resin impregnation (61,62). The composite skeletons were prepared from Sigrafil HM 3 PAN-based fiber, rigidized with a phenolic resin, and densified by four cycles with coal-tar pitch plus sulfur the carbonization temperature was 1000°C. (a) Young s modulus.

The change of the relaxation modulus with composition at 120°C is given in Figure 5. The sudden increase of the relaxation modulus between 0.3-0.4 volume fraction of PC is attributable to the increasing continuity of the PC phase. As a consequence, the mechanical response of the blend becomes more and more dominated by the rigid PC phase, as this phase increases in continuity throughout the whole polymer mass. 

Additional increase of properties of titanium-based materials is associated with composites. For example, reinforcement due to continuous fibres of silicon carbide (up to 40-wt.%) permits strength and rigidity of such materials to be essentially increased. However, the cost of such composites appears to be prohibitive (about several tens of thousands of USD per 1-kg [19], Moreover, above temperatures of 600 °C an interaction of fibers and matrix is revealed. 

While rigid hard stamps are successfully used to print submicron features, elastomeric stamps remain attractive because they can be easily fabricated and they readily conform to rigid substrates at ambient pressures. The low elastic modulus and high compressibility of elastomeric PDMS stamps can be overcome with composite PDMS stamps (/t-PDMS) [22,23]. As discussed in Section 5.5.2, /t-PDMS stamps consist of a Sylgard 184 PDMS layer that provides conformal contact with... 

In terms of equipment. McDonnell Douglas proposes an automated ultrasonic scanning system (AUSS) with 9 axes of motion, a 7 axes ultrasound system (ADIS-II) and a portable inspection system (MAUS II) for aerospace composite structure inspection [36], The ultrasonic resin analyser (URA 2002A from Quatro Technologies) can be used to measure the resin content in polymer based composites [10]. The UCMS-200 ultrasonic cure monitoring system from Micromet Instruments utilizes measurements of the ultrasonic sound speed to monitor changes in the viscosity, rigidity of composites. 

Figure 3.2. Scanning electron micrographs of mechanically polished rigid conducting composite electrodes based on (A) Araldite-M-graphite (73.2%3, [B) Araldite-CW2215-graphite (45.8%), (C) silicone-graphite (61,0%), (D) epoxy-H77-graphite (20.0%) (Adapted with permission from Analyst 2002, 127, 1512-1519. Copyright 2002, The Royal Society of Chemistry).

When a rigid and bulky diol is used as the chain extender, harder elastomers of higher modulus are produced. It can be seen in Table 3.14 that a toluene diisocyanate-based composition (A) from the bulky diol 1,4-dihydroxy-1,2,3,4-tetrahydronaphthalene is inferior in tensile properties to the diphenylmethane diisocyanate-based material (C), although composition (A) is superior to the elastomer from 1,4-butane diol (B). A similar situation can be seen with composition (E), where a,a -dihydroxyxylene was used, compared with composition (D) based on 1,4-butane diol. 

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