Composite degradation

Wool, R. P. 1995. The science and engineering of polymer composite degradation. In Degradable polymers Principles and applications, eds. G. Scott and D. Gilead, 141. New York, NY Chapman and Hall. 

Used in conjunction with certain metal chelate compounds in rendering polyolefin compositions degradable... 

The development of an amorphous fiber in the Si-N-C-B system has revealed two unexpected possibilities. First, this fiber appears to be stable in the amorphous state up to 1,600°C (2,912°F), even in air, and retains its tensile strength up to 1,600°C (2,912°F). Second, oxidation of the Si-N-C-B fiber forms silica at rates comparable to the rate that silica is formed upon oxidation of crystalline SiC, and also creates a thin ( 50 nm [0.002 mils]) buried interphase of hexagonal BN. It has been hypothesized that this in-situ BN would act as a crack deflection layer in a CMC. If so, the regenerative nature of the deflection interphase could avert composite degradation by stress oxidation. 

At high temperatures (> 600°C) the composites degrade in strength and toughness due to oxidation of C fibers and/or these interface layers and prevention of fiber pullout (brittle fracture mode). Studies are in progress to increase oxidation resistance by use of a CVD-SiC overlayer which seals the surface of the porous composites. 

Mohamed, A.A., Finkenstadt, V.L., Palmquist, D.E. and Rayas-Duarte, P. (2009) Thermal properties of extmded injection-molded poly(lactic acid) and milkweed composites Degradation kinetics and enthalpic relaxation. Journal of Applied Polymer Science, 111, 175-184. 

The peak temperatures for thermal degradation of the composites and the PP matrix occurred at approximately 458°C and 450°C, respectively. Table 6.4 shows that the addition of fibers caused a significant increase in the peak temperature for composite degradation, reaching 466°C for the composites reinforced with 20 wt% fibers treated with hot water. 

Quantitative measurements were also made from p-CT images to determine the porosity of the composites. It was found that the porosity of the composites varied depending on their manufacturing method porosity was 0.3% of total sample volume for in situ polymerised composites whereas it was 0% for infiltrated composites. The authors concluded that the in situ polymerised composites degraded as a bulk with faster degradation in the centre of the sample, whereas the polymer phase in infiltrated composites appeared to degrade as individual spheres with faster degradation in the centre of each sphere. 

As previously mentioned, mechanical properties of polymer composites degrade at elevated temperatures. This degradation is more pronounced for... 

Because of the need for strength in structural applications, thermoset polymers are usually used with fiber reinforcement, the most common of which is fiberglass. Since there are now several different materials forming the composite, degradation of the composite can be complex because each material can degrade separately or simultaneously. In addition, there are concerns about the degradation of the interface between the polymer and reinforcement. 

Structure composition/degradation evolved gases with increasing T, solvent identification/ quantitation stoichiometry... 

Figure 4.10 PVA/BC composites degraded over time by a single fungal strain. Reproduced from [207] with permission from Springer.

Pihlatie, M.H., Kaiser, A., Mogensen, M. Chen, M. Electrical conductivity of Ni-YSZ composites Degradation due to Ni particle growth. Solid State Ionics 189 (2011), pp. 82-90. 

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