Heat stabilizers, additive composite

Cost bilizers. In most cases the alkyl tin stabilizets ate particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyl tin mercaptides. Mercaptans are quite effective costabilizets for some of the alkyl tin mercaptides, particularly those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyl tin mercaptide ate currendy the most efficient stabilizers for PVC extmsion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roU mill performance of some methyl tin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. 

Recognition that heat stabilization of the plasticizer as well as the PVC resin was necessary greatly assisted researchers working on the problem. Epoxy compounds perform both functions. Today, they are part of many stabilization systems for vinyl compositions, so much so that worldwide use approaches 400 million pounds. In addition to vinyl stabilization, they are also used in phosphate ester functional fluids (i.e., fire-resistant hydraulic fluids) where acid development must also be avoided. 

Even when PPS has superior chemical resistance and heat stability, its brittleness may be a drawback for certain applications. The physical properties of PPS can be improved by the addition of small amounts of terpolymers of ethylene, methylacrylate, and glycidyl methacrylate, also in a grafted variant with poly(methyl methacrylate) [59]. The manufacture of the composition occurs by melt mixing under a high shear rate. 

Lugao and his group had introduced a new procedure to determine OIT in non-stabilized, stabilized, irradiated, and nonirradiated PP. The new procedure was based on two main features (1) starting the oxidation on melted samples at temperatures as low as possible and (2) oxidation under slow heating conditions. Since each sample has a set of two values of time and temperature, it is called as temperature-dependent oxidative induction time. This new method is found to be reproducible, sensitive (to small changes in additive compositions), simple, and inexpensive (Lugao et al. 2002). 

As mentioned above, a limited thermal stability of PVC requires the addition of heat stabilizers in almost all fields of application. Besides, also other additives (e.g., light stabilizers, fillers, lubricants) are used to modify the properties of PVC or to improve its processability. At present, about 1/3 of all used PVC is plasticized by various types of modifiers. Therefore, it is helpful to get some detailed information about the composition of a special PVC scrap before re-use. 

To the LC polyester composition additives can also be used in the form of antioxidants and heat stabilizers such as a hindered phenol, hydroquinones, phosphites etc. Another additives, also added as required, can be mentioned as, ultraviolet absorber (resorcinol, salicylate etc.), color protecting agent (phosphate, hypo-phosphite etc.), lubricant and mold lubricant (stearyl alcohol, stea-ramide etc.) [137]. 

The nature of the surfactant used in the redox polymerization is said to have an effect not only on the average particle size but also the size-distribution, the heat stability of the polymer, the percent solids of the produced lattices, and the stability of compositions involving post-additions to a latex. A recently published seed polymerization recipe prepares the seed in appropriate equipment by adding to 1300 gm of deionized water, 0.15 gm of sodium bisulfite, and various amounts of a surfactant, and 815.0 gm of vinyl chloride. To this mixture is added a solution of 48.0 gm of deionized water, 2.0 gm of 30% aqueous ammonia, and 0.04 gm of potassium persulfate. Then a stream of 7.24 gm of the surfactant Dowfax 2A1 (45%) in 192.76 gm of deionized water is pumped in along with a stream of 399.96 gm of deionized water, containing 0.40 gm of potassium persulfate. This formed the seed latex. 

Thermal stability of elastomer can be assessed from the weight loss as a function of temperature. TGA thermograms of pure NR and its composites have been shown in Fig. 4 [65]. Conventional carbon black (CB) dispersed in NR caimot increase the thermal stability of NR while CNT dispersed in NR increase the degradation temperature significantly mainly due to thermal barrier of the nanoparticles. Another reason for this improvement might be due to restriction on the mobilization of rubber macromolecules in presence of CNT and carry out heat homogeneously and avoid heat concentration [88]. On the other hand, Falco et al. has shown similar thermal stability of composites to that of pure SBR with the addition of MWCNT [29]. 

The 100% linearity of PX-316 imparts superior low temperature flexibility to vinyl compositions, and demonstrates excellent light and heat stability, as well as low volatility. Addition of PX-316 to plastisols and organosols lowers initial viscosity and leads to longer shelf life. 

The miscibility of PVC and chlorinated PE and the effect of the blend composition on the heat stability of the PVC were investigated using several techniques, including TGA and DSC. The apparent activation energy of PVC dehydrochlorination in the blends was calculated and experimental TGA curves compared with those predicted using the additivity rule. It was found that the blends were heterogeneous and that addition of chlorinated PE in a specific temperature range resulted in an improvement in the heat stability of the PVC. 22 refs. 

Yagneswaran and co-workers [25] incorporated mechanically devulcanised waste tyre powder into a vinyl ester resin matrix at various levels of addition and characterised the resulting materials using physical tests, DSC and TGA. As the level of rubber powder increased the composites were found to have reduced heat stability and flexural strength, but increased flexural modulus. 

Wang et al. [96] reported a decrease of char residue by increasing the amount of OMMT in addition-type sihcone rubber composites, whereas the initial and center temperatures of thermal degradation of these samples showed first an increase followed by decrease. Similar behavior was reported for hydroxyl-containing (condensation type) sihcone rubber composites, that are known to vulcanize via dehydration of the hydroxyl end groups [97]. It was concluded that there are two factors influencing the thermal stability of composites (i) the incorporation of efficiently dispersed OMMT, that can prevent heat transport and thus improve the thermal stability of composites, and (ii) the OMMT contains some molecules that are able to evolve even at low temperatures and, some of them, would certainly impair the thermal stability of composites. 

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