Long-term thermal stability

Another class of additives for polypropylene stabilizations is compounds containing a 2,2,6,6-tetramethyl piperidyl group (I). These compounds are frequently referred to as 

A triazine compound, Ethanox 314, of the following structure by Albemerie Corp. has a moderate molecular weight of 784 and a melting point range of 218-223°C [118]. It is claimed to retard thermooxidative degradation in various polymers and to enhance their light stability. The antioxidant exhibits high resistance to extraction and low volatility  

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Polyimides are high-performance technical polymers mainly used for their short- and long-term thermal stability. 

As with drugs and purified biomarkers, thermal- and photostability of botanical products are the factors that must be considered. Commercial dried extract and capsules of SJW were evaluated under harmonized test conditions (25). Photostability testing showed all the constituents to be photosensitive in the tested conditions. However, different opacity agents and pigments influenced the stability of the constituents. Amber containers had little effect on the photostability of the investigated constituents. Long-term thermal stability testing showed a shelf life of less than four months for hyperforins and hypericins, even when ascorbic and citric acids were added to the formulation. 

The paucity of vapor pressure data is not surprising because these compounds generally have low volatility compared to other species that have been used as precursors for CVD (e. g., WF6 exhibits a vapor pressure of 1000 torr at room temperature )50 and are frequently plagued with problems such as lack of long-term thermal stability (ligand dissociation). Unfortunately, it is not possible to make an unambiguous direct comparison of the volatility of different species from comparison of their sublimation temperature, because no information is provided on the rate of sublimation. In this review, we report the sublimation temperatures and use this as an approximate guide to make qualitative comparisons of apparent volatility between precursors where we feel it is reasonable to do so. 

The so-called Kneisl-Test is a simple method which can be used for the estimation of the long-term thermal stability, particularly for primary explosives. A defined quantity (e.g. 100 mg) of the substance under investigation is air sealed in a glass ampoule. This ampoule is then placed in an oven for 100 h at the temperature for which thermal stability should be determined. The ampoule is then opened, the remaining mass of substance weighed and any gaseous decomposed products... 

Fulgides and related diarylethenes have been investigated extensively because of the long-term thermal stability of their photocyclized colored forms, which could lead to this application in erasable optical recording materials and photoswitchable optical elements. The entrapment of these photochromic molecules in polymer films is necessary for these practical applications. Picosecond laser photolysis was employed to study the electrocyclic reaction of a furylfulgide (18, Figure 8) in polymer solids and revealed that the colored structure was formed with a time constant of ca. lOps irrespective of the nature of the polymer matrix.49... 

Phenolic antioxidants are well known for being melt processing stabilizers as well as long-term thermal stabilizers. In the chemiluminescence measurements on the polyethylene films under oxygen (Fig. 3.3), the antioxidant effect of the phenols is clear when these induction times are compared with those of the free additive polyethylene film (0.73 h) (Table 3.2). The results showed that the structure of the phenolic moiety will be a cmcial factor influencing the stabilization performance. 

The high efficiency of Irganox 1010, as a long-term thermal stabilizer in polyethylene film, was evidenced by the increased oxidation induction time (OIT) (Table 3.4). 

The long-term thermal stability between 350 and 450°C for a composite Pd porous stainless steel membrane with an oxide intermetallic diffusion barrier layer is shown in Fig. 13.7. As shown in the figure, the membrane showed no sign of deterioration after over 6,000 h of continuous testing. 

Fig. 13.7 Long-term thermal stability of composite palladium-porous stainless steel membrane...

Examples of widely used secondary antioxidants are phosphites, phosphonites, and sultides (Fig. 11.7). Usually, secondary antioxidants are used in combination with primary antioxidants to benetit from a synergistic effect. The main action of phosphites and phosphonites is the oxidation to the corresponding phosphates by reacting with hydroperoxides. These P compounds are mainly used as melt stabilizers during processing. Sulfur compounds act as well as hydroperoxide decomposers via sulfur oxide and sulfenic acid formation. Sulfur compounds are preferably used in combination with phenolic antioxidants to improve the long-term thermal stability of polymers at temperature ranges between 100 and 150 °C. 

Polymer Long-Term Thermal Stability in Days at°C, Unstabilized Long-Term Thermal Stability in Days, 0.2% Antioxidant (AO)... 

Figure 11.9 Influence of (nano)flllers on long-term thermal stability of polypropylene (P).

Long-Term Thermal Stability and Chemical Compatibility... 

The polymers were characterised by NMR and matrix assisted laser desorption/ ionisation-time of flight MS (MALDI-TOF MS) [92]. They have variable indices of refraction (from 1.45-1.52), Tg from 265-350 °C, and long-term thermal stability at 623 K. The dependence of refractive index on wavelength were also measured and the constants of copolymerisation reaction were determined [92]. End-group analysis has been a reliable asset in PFCB chemistry and in particular for copolymerisation studies [92]. 

Silicone resins and composites produced with silicon resins exhibit outstanding long-term thermal stability at temperatures approaching 572°F (SOO C) and excellent moisture resistance and electrical properties. These materials are also useful in the cryogenic temperature range. 

Hindered Amine 192268-64-7 Chimassorb 2020 2600-3400 120-150 pellets Light stabilizer for POs also provides long-term thermal stability for filled PP articles... 

Better long-term thermal stability than phenolics. 

Since most stabilizers react in more than one way and combinations of additives are required to prepare stabilized polypropylene fiber, these materials are better discussed in accord with the function they perform for polypropylene rather than the mechanism by which they function. When making fibers, stabilizers are added to polypropylene to (1) provide melt extrusion stability (2) provide long-term thermal stability at normal use temperatures and (3) provide stability to exposure to UV light (sunlight). The degree to which these stabilizers effectively accomplish their objectives without introducing other objectionable effects, such as yellowing, determines the value of the resultant fiber product. 

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