Menachem Lewin

Synergistic and Catalytic Effects in Flame Retardancy of Polymeric Materials— An Overview:

Synergistic and antagonistic effects of two or more additives are often encountered in flame retardancy of polymeric materials. Halo gen-antimony synergism is the best known. Evidence for bromine-ammonium, bromine-chlorine and bromine-phosphorus synergisms has been observed in some systems. Useful phosphorus-nitrogen synergism has frequently been ob served and has been studied in detail, with the result that various postulates can explain the effect. Combinations of phosphorus compounds are sometimes syner gistic and various combinations of phosphorus with intumescent char-forming agents are often highly efficacious as flame retardants.

Enhanced Flame Retardancy of Polypropylene with Magnesium Hydroxide, Melamine and Novolac

It has been found that, even at levels of magnesium hydroxide too low to impart flame retardancy to polypropylene, the addition of melamine makes it possible to reduce burning time under UL 94 conditions sufficiently to meet the V-2 rating. However, flaming drips still persist, so that a V-0 rating by UL 94 can not be obtained. It was then found that by the further addition of a novolac at lev els as low as 1%, together with melamine, a UL 94 V-0 rating could be reached. Levels of magnesium hydroxide could be as low as 30-50%, allowing the formula tion to be flexible. The novolac caused a useful dimension-stabilizing effect above the melting point of polypropylene. Some thermal evidence suggested that a novolac-magnesia gel may be formed.

Flame Retarding of Polymers with Sulfamates. I. Sulfation of Cotton and Wool

Some results of work carried out on flame retarding of cotton and wool fabrics are reviewed.* Cotton fabrics are rendered flame retardant upon treatment with ammonium sulfamate (AS) with urea or a urea-based cross linking agent, as co-additive, in the pad-dry-cure finishing treatment, with curing at 180-200°C for one to three minutes. Wool fabrics are similarly treated with sul famic acid (SA) in the presence of urea at 140-160°C. In both cases a very high de gree of flame retardancy is obtained and the treated fabrics pass the vertical strip test (VST) also after fifty hard water alkaline launderings. In both cases, the fab rics retain their soft hand. In order to overcome the afterglow in cotton, a com bined sulfation-phosphorylation process was developed.

Flame Retarding of Wood by Chemical Modification with Bromate-Bromide Solutions

In spite of the extensive and diversified uses of wood and wood products for millenia, there are still a number of basic deficiencies of these pro ducts which limit their use and pose difficult and as yet not satisfactorily solved problems to the engineer and consumer. The most prominent of these problems are: flammability, dimensional stability, and fungal attack. Review of work carried out at the Israel Fiber Institute indicates that treating solid timber and polywood with acidified bromate-bromide solutions is capable of overcoming these deficiencies to a large extent. The treatment is carried out in autoclaves with application of vacuum and pressure. The lignin component of the wood is brominated in the solid state by the treatment solution with a high yield of bromine. The mechanical properties of the treated products are un changed. The treatment is stable to prolonged leaching, aging, and storage. Water absorption and swelling are drastically decreased-dimensional stabi lization. The brominated products are shown not to be attacked by wood fungi.

Crystallization kinetics of poly(ethylene terephthalate) studied by rapid scanning Raman spectroscopy

Abstract Rapid scanning Raman spectroscopy is used to follow the process of crystallization of poly(ethylene terephthalate) in the solid state. This new application of Raman spectroscopy to a chemical problem indicates the presence of multiple stages in the crystallization. The origin of these stages is discussed. The technique also permits the first examination of crystallization kinetics at the functional group level. The results show that activation energies as well as the Avrami n and k parameters are different for different functional groups. Data from rapid scanning Raman spectroscopy are compared with recent i.r. data on this process, and with results from other techniques.

Raman Spectroscopy Applied To Polymer Analysis: Low Frequency Spectra Of Polyester Fibers

Among the many advantages of Raman spectroscopy for polymer characterization, low frequency data have been the least exploited. Results are presented on the use of low frequency Raman data on polyester fibers for determining the relative specific heats, and the degree of amorphous orientation. Background theory is presented.