Long-term aging

During the vulcanization, the volatile species formed are by-products of the peroxide. Typical cure cycles are 3—8 min at 115—170°C, depending on the choice of peroxide. With most fluorosihcones (as well as other fluoroelastomers), a postcure of 4—24 h at 150—200°C is recommended to maximize long-term aging properties. This post-cure completes reactions of the side groups and results in an increased tensile strength, a higher cross-link density, and much lower compression set. 

The polarity of the polyethers makes them incompatible with hydrocarbon-type plasticizers, which tend to bleed. Effective plasticizers are ethers such as di(butoxyethoxyethyl)formal [143-29-3] (Thiokors TP-90B), esters such as di(2-ethylhexyl) phthalate [117-81-7] dioctyl phthalate (DOP), polyesters such as Paraplex G50 (Rohm and Haas), and ether—esters such as di(butoxyethoxyethyl) adipate [114-17-3] (Thiokol s TP-95). The lower mol wt plasticizers, DOP, TP-90B, and TP-95 improve vulcanizate low temperature performance. The polymeric plasticizers maintain higher temperature and long-term aging properties. Epoxidized plasticizers should be avoided because they interfere with vulcanization. 

T. Ohmura, K.Tsuzaki, K. Sawada, and K. Kimura, Inhomogeneous Nanomech-anical Properties in the Multi-phase Microstructure of Long-term Aged Type 316 Stainless Steel, Jour. Mater. Res., 21,1229 (2006). 

A report (37) on the effect of different types of radiation on the elongatlon-at-break of certain commercial cable Insulating materials pointed to several aspects requiring fundamental Investigations on well-characterised materials under defined conditions. It showed the Importance of antl-oxldant stabilisers, particularly In relation to long term ageing. It was concluded that the differences observed could be attributed to dose rate effects rather than to the types of radiation studied. The Irradiated samples were standard dumb hell shaped tensile samples. 

For a given level of fuel at a given thickness with the same halogen content, most halogenated compounds show more or less the same flame retardancy. The key differences among these FR additives are effects on flow, melt stability, mechanical properties and long-term ageing of the FR-PBT blend. Different end-use requirements may call for the addition of different FR additives. 

Uncured poly(GlyN) prepolymer exhibits good chemical stability and has a satisfactory shelf-life. However, the ageing characteristics of isocyanates cured PU rubbers are unsatisfactory contrary to (NiMMO) rubbers which have good ageing characteristics. Long term ageing trials have shown that the cured... 

R.M. Streicher, Sterilization and long-term aging of medical-grade uhmwpe, Radiat. Phys. Chem., 46 893-896, 1995. Proceedings of the 9th International Meeting on Radiation Processing, 1994, Pt. 1. 

IEC 61244-1, 1993. Determination of long term ageing in polymers. Part 1 Techniques for monitoring diffusion limited oxidation. 

Short-term studies indicate that Thermopave mixes generally attain their ultimate stability after a curing time between one to five days, depending upon the sulfur/asphalt ratio and sand type. The results of a long-term aging study of Marshall briquettes stored at room temperature are presented in Table V. The data indicate a random variation in stability values but no significant change in stability over a five-year period. 

Guo, J.-H. Robertson, R.E. Amidon, G.L. Influence of physical aging on mechanical properties of polymer free films the prediction of long-term aging effects on the water permeability and dissolution rate of polymer film-coated tablets. Pharm. Res. 1991, 8 (12), 1500-1504. 

Figure 62 Retention of compressive strength under long-term aging test (12).

Hahgenated polymers, both brominated and chlorinated, have been developed to yield better polymer compatibility, improve physical properties, and long-term-aging characteristics in many thermoplastic resins, particularly the high-performance engineering thermoplastics, such as nylon, polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). These materials still use antimony oxide as a synergist to achieve the desired flame resistance (31). 

Finally, it has been shown by de Lange et al. [43,61] that ageing of the calcined membranes changes their microstructure. Long-term ageing under ambient conditions (i.e. 16 months at 20°C) or 80 days at 40°C and 60% RH results in a few percent loss of porosity of non-supported layers. Ageing at 350°C for 10 days in an air atmosphere containing 1.7% H2O vapour caused a porosity decrease from 27 to 25%. 

In the Neoprene G tests summarized In Figure 1 and Table I the outer (dry) faces of the permeated rubber samples were washed with DI water to determine If soluble salts were present. The conductivity values listed In Table I show only a very slight difference, t lch Is probably of little Import. The Internal water permeant was, however, changed by the long term aging. 

Evolution of Some Physical Properties of "Aceto Balsamico Tradizionale Di Reggio Emilia" during Long-Term Aging... 

---