Resins, properties thermal degradation

Recently, several reports of the flame-retardant properties of boron-containing bisphenol-A resins have appeared from Gao and Liu.89 The synthesis of a boron-containing bisphenol-A formaldehyde resin (64 and 65) (Fig. 42) from a mixture of bisphenol-A, formaldehyde, and boric acid, in the mole ratio 1 2.4 0.5, has been reported.893 The kinetics of the thermal degradation and thermal stability of the resins were determined by thermal analysis. The analysis revealed that the resin had higher heat resistance and oxidative resistance than most common phenol-formaldehyde resins. 

Illustrative performance properties for a "general purpose polycarbonate," and for the same resin modified with the additive formulations "700" (without PTFE) and "800" (with PTFE) are summarized in Table IV (adapted from reference 32). It is clear that the objective of minimal effect on performance properties has been attained for this system. It is evident that flame retardant effectiveness attained with minimal levels of additive can provide optimum solutions to the problem of decreasing flammability without sacrifice in performance properties. Work documented to date suggests that in depth studies of thermal degradation such as reported for aromatic sulfonates in polycarbonates (28) would be rewarding for other systems. 

For high temperature and rubber-modified epoxy resins, thermal degradation events and the cloud point curve are included on the diagrams, respectively. Two degradation events have been assigned devitrification, or a glass-to-rubber event and revitrification, which is associated with char formation. The cloud points and depressions of Tg for different rubber-modified epoxies can be compared and related to volume fractions of the second phase and to the mechanical properties of the cured materials. 

Figure 3 shows a thermogravimetric analysis performed on the two molding compounds. The scans show that the molding compound based on the stable bromine CEN has a 15-20°C increase in thermal degradation temperature over the standard compound. Even though the stable bromine CEN is more thermally stable than standard resins, it still supplies the bromine necessary to achieve the desired flame retardancy properties. 

MAJOR APPLICATION H-H PVC is mostly studied in academic field to understand its structure/property relationship, thermal degradation behavior, and mechanism. Its properties are compared to those of commercial head-to-tail PVC. Pure H-H PVC has no significant industrial applications. H-H PVCs containing 40-65 wt% of Cl, also called chlorinated polybutadiene rubber-resins, are used for coating, paint-based applications and the preparation of threads, tires, tubings, and films, etc. 

Coal dust is usually added to green sand for cast iron moulding. It is used to a limited extent in some non-ferrous foundries. Coal dust may be mixed with small amounts of resins and oil products. During casting, the thermal degradation produces lustrous carbon , which improves the casting surface finish and shake-out properties. Coal dust is added for three reasons ... 

Py-GC/MS techniques have been used in general for thermoplastics and some examples are presented here, but some recent studies on pyrolysis and thermal degradation of thermosets were carried out. ° These resins lose their properties and become brittle solids after curing, and consequently they are neither fusible nor soluble in any solvent. Therefore direct chromatographic analysis of cured resins is not possible, unless Py-GCY MS is used. 

Huntite (Mg3Ca(C03)4) was used as reinforcement for an unsaturated polyester resin [53]. A content of 3 % huntite had a reinforcing effect for the resin, which caused an improvement of the mechanical and thermal properties. Regarding the thermal behavior, the onset temperature of composites thermal degradation was increased with approximately 50 °C, while the maximum degradation temperature was improved with 16 °C, compared to the polyester matrix. 

Schutz et al. studied the thermal properties of a phenolic resin nanocomposite containing silsesquioxanes [80]. The thermal oxidative stability of the nanocomposites was improved, as compared to that of the piu e resin. This effect may be a consequence of the formation of a protective layer of SiG2 during silsesquioxanes pyrolysis at the surface of nanocomposites, which retarded the thermal oxidative degradation. The temperatures characteristic to thermal degradation processes were higher in the case of nanocomposites, compared to the pure resin matrix. 

Jash and Wilkie [86] reported that even when the fraction of clay was as low as 0.1 wt% the PBQiR in a cone calorimeter was lowered by 40 %. Lee et al. [87] demonstrated that incorporation of 6, 8 and 10 wt% of MMT into epoxy resin increased linearly the char yield firom 9.1 to 15.4 % reducing the thermal degradation of the epoxy matrix. Nazare et al. [88] studied the flammability properties of unsaturated polyester resin with nanoclays using cone calorimetry. The authors verified that the incorporation of 5 wt% of nanoclays reduces the PHRR by 23-27 % and THR values by 4-11 %. While incorporation of condensed-phase flame retardants (such as ammonium polyphosphate, melamine phosphate and alumina trihydrate) reduce the PHRR and THR values of polyester resin, the inclusion of small amounts of nanoclay (5 % w/w) in combination with these char promoting flame retardants causes total reductions of the PHRR of polyester resin in the range 60-70 %. Ammonium polyphosphate, in particular and in combination with polyester-nanoclay hybrids show the best results compared to other flame retardants. 

Hong et al. [231] have used this simple technique for the synthesis of ZnO-low-density polyethylene composites. ZnO nanoparticles and branched low-density polyethylene was melt-compounded in a high-shear mixer to prepare polymer nanocomposites with an improved resistance to thermal degradation. They also mixed submicron-sized ZnO particles with low-density polyethylene for a comparison and reported that the surface properties of nanoparticles (<100 nm) resulted in an increased thermal stability of nanocomposites. Ma et al. [232] also used melt blending for the synthesis of silane-modified ZnO-polystyrene resin nanocomposites. Incorporation of ZnO nanoparticles results in an increased flexural... 

When processing the resin at, or near, the upper limit of the recommended melt temperature range, the shot size should approach 70 to 80% of the machine s barrel capacity. If the cylinder temperature exceeds the upper limit of the suggested melt range, thermal degradation of the resin and loss of physical properties may result. 

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