Antioxidant action in polymers
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Additives for Polymers June 1993 bound to a much lower extent. Initial cross- linking occurs followed by structural rearrangement of the crosslinked product to give gel-free homogeneous polymer grafts that melt blend with unmodified poly- propylene. (5 refs). Polymer Degradation & Stability, 1993, 40, 233-238 Fire retardant properties of polyesters Zinc hydroxystannate and zinc stannate are effective flame retardant synergists when used at levels of up to 5 phr in polyester resins containing additive-type halogen compounds. The degree of synergism exhibited depends on the chemical nature of the halogen source and its level in the resin formulation. ZHS and ZS also act as smoke suppressants in these systems, although the effects are somewhat less pronounced than those previously observed in polyesters based on reactive-type halogen compounds. Polymer Degradation & Stability, 1993, 40, 267-2 73 Thermoanalytical investigations indicate that the tin additives operate as fire retardants by a combined condensed/vapour phase action. Although ZHS and ZS generally promote char formation during thermal degradation of the polymer, a vapour phase flame-retardant action predominates in systems where the ratio of halogen to metal is very high. (30 refs). Polymeric microspheres Spherical particles with sizes from tenths of a micrometer to several micrometers formed from synthetic or natural polymers are known as microspheres. Larger particles are also sometimes named microspheres. Currently the nomenclature has become more precise and the particles are divided into nanospheres (particles with diameters D = IOOnm), microspheres (O.lpm 5 D I 50 pm) and millispheres (50 pm 5 D I 500 pm). Polymeric microspheres have in recent years Znt. Polymer Science & Technology, 1992, become useful tools in basic research and in practical 12, T102-109 applications in chemistry, biochemistry, physics, biology, medicine and veterinary work. The present article presents some of the most important methods of microsphere preparation, the methods of measurement of their basic properties and some examples of their applications mainly in medicine and biology. The article was prepared using the lectures presented at the Polish symposium “Polymeric micro and millispheres - preparation and applications in medicine, biology and biotechnology”, Ladz, 1991, and from publications of work presented at meetings of the American Chemical Society in the years 1986, 1990 and 1991. Microspheres can be prepared directly during polymerization (eg emulsion of dispersion), by cooling the emulsified molten polymer, cooling of drops of the polymer extruded through a special die, or by removal (evaporation) of solvent from the emulsion of the polymer solution. Methods have been developed for the direct synthesis during polymerization of microspheres of uniform size. The correct choice of the polymerization conditions, monomer concentration and type and concentration of the surface active agent, can, within limits, regulate the size of the microspheres. The diameters of the smallest microspheres obtained by this method are 0.1 pm, the largest do not exceed 3 pm. (66 refs). Antioxidant action in polymers One of the ways of increasing antioxidant effectiveness is the use of chemical synergism-substitution of a single antioxidant by a mixture of several. This type of synergism may be observed in both low- molecular-weight and high-molecular-weight materials. In this paper we demonstrate another type of synergism in polymers, non- chemical synergism arising from the specific features of a polymer as the reaction medium, The basic principles of such synergism are discussed. (7 refs). O1993 Elsevier Science Publishers Ltd 8
Transcript of Antioxidant action in polymers
Additives for Polymers June 1993
bound to a much lower extent. Initial cross- linking occurs followed by structural rearrangement of the crosslinked product to give gel-free homogeneous polymer grafts that melt blend with unmodified poly- propylene. (5 refs). Polymer Degradation & Stability, 1993, 40, 233-238
Fire retardant properties of polyesters
Zinc hydroxystannate and zinc stannate are effective flame retardant synergists when used at levels of up to 5 phr in polyester resins containing additive-type halogen compounds. The degree of synergism exhibited depends on the chemical nature of the halogen source and its level in the resin formulation. ZHS and ZS also act as smoke suppressants in these systems, although the effects are somewhat less pronounced than those previously observed in polyesters based on reactive-type halogen compounds.
Polymer Degradation & Stability, 1993, 40, 267-2 73
Thermoanalytical investigations indicate that the tin additives operate as fire retardants by a combined condensed/vapour phase action. Although ZHS and ZS generally promote char formation during thermal degradation of the polymer, a vapour phase flame-retardant action predominates in systems where the ratio of halogen to metal is very high. (30 refs).
Polymeric microspheres
Spherical particles with sizes from tenths of a micrometer to several micrometers formed from synthetic or natural polymers are known as microspheres. Larger particles are also sometimes named microspheres. Currently the nomenclature has become more precise and the particles are divided into nanospheres (particles with diameters D = IOOnm), microspheres (O.lpm 5 D I 50 pm) and millispheres (50 pm 5 D I 500 pm).
Polymeric microspheres have in recent years
Znt. Polymer Science & Technology, 1992,
become useful tools in basic research and in practical
12, T102-109
applications in chemistry, biochemistry, physics, biology, medicine and veterinary work. The present article presents some of the most important methods of microsphere preparation, the methods of measurement of their basic properties and some examples of their applications mainly in medicine and biology. The article was prepared using the lectures presented at the Polish symposium “Polymeric micro and millispheres - preparation and applications in medicine, biology and biotechnology”, Ladz, 1991, and from publications of work presented at meetings of the American Chemical Society in the years 1986, 1990 and 1991. Microspheres can be prepared directly during polymerization (eg emulsion of dispersion), by cooling the emulsified molten polymer, cooling of drops of the polymer extruded through a special die, or by removal (evaporation) of solvent from the emulsion of the polymer solution. Methods have been developed for the direct synthesis during polymerization of microspheres of uniform size. The correct choice of the polymerization conditions, monomer concentration and type and concentration of the surface active agent, can, within limits, regulate the size of the microspheres. The diameters of the smallest microspheres obtained by this method are 0.1 pm, the largest do not exceed 3 pm. (66 refs).
Antioxidant action in polymers
One of the ways of increasing antioxidant effectiveness is the use of chemical synergism-substitution of a single antioxidant by a mixture of several. This type of synergism may be observed in both low- molecular-weight and high-molecular-weight materials. In this paper we demonstrate another type of synergism in polymers, non- chemical synergism arising from the specific features of a polymer as the reaction medium, The basic principles of such synergism are discussed. (7 refs).
O1993 Elsevier Science Publishers Ltd 8
June 1993 Additives for Polymers
Polymer Degradation & Stability, 1993, 40, (31, 33 7-341
Stability of additives in polythene and aliphatic polyamides
The solubility of diphenylamine, phenyl benzoate and diphenyl methane in high- density polyethylene and various polyamides has been studied as a function of oxidation and of sample annealing.
Oxidative destruction of topological structures forming the non-polar sorption centres and accumulation of new-formed polar groups, participating in sorption of polar compounds, result in complicated dependencies of solubility upon oxidation, in some cases showing minima. (8 refs). Polymer Degradation & Stability, 1993, 40, (3), 36368
Photolysis of a commercial hindered amine light stabilizer
The photolysis of a commercial hindered amine light stabilizer (HALS) has been studied with a range of experimental methods. The results show that the stabilizer is easily photolyzed and photolysis mechanisms are proposed. (4 refs). Polymer Degradation & S&ability, 1993, 40, (3), 375-378
ENVIRONMENTAL ISSUES
CFC-containing foams banned
EPA has promulgated a final rule banning the sale of plastic foams produced with chlorofluorocarbons as the blowing agent. The rule, effective 4 January 1994, implements a section of the Clean Air Act that prohibits non-essential products that use or contain the ozone-depleting chemicals CFCs, halons, carbon tetrachloride, and 1 ,l , I-trichlorothane, EPA believes that viable substitutes are available for both rigid and
flexible foams made for packaging, insulation and other applications.
Test data for EPA on fire retardants and crosslinking agents
According to TSCA Section 4(a) Test Rules, EPA is concerned about possible brominated dioxin species formation in the production of brominated aromatic flame retardants. EPA has received voluntary test data from AmeriBrom Inc on polybrominated dibenzo- dioxins and dibenzofurans analysis of tetrabromobisphenol-A and decabromo- diphenyl oxide, and the same from Great Lakes Chemical Corporation for the ally1 ether of tetrabromobisphenol-A. Also, data were received from CMA consisting of bone- marroiv micronucleus assay for 4-vinyl- cyclohexene, used as a cross-linker. These data were required by negotiated test rules under TSCA.
COMPANY NEWS
Elf Atochem in Chinese additives agreement
France’s Elf Atochem group and Beijing Chemical Industry Group have signed a contract to establish a joint venture for the manufacture of plastics additives. The new organization, called Beijing Elf Atochem Polystab, will produce and commercialize the existing range of organotin products from BCIGC with those manu-factured using Elf Atochem technology. The company is 60% owned by Elf Atochem with the remainder held by BCIGC. The materials are employed as stabilizers for PVC Contact: Elf A&hem, 4 tours Michelet, La Defense IO, F-92091 Paris La Defense, Cedex 42, France.
Bayer titanium dioxide manufacturing activities
Bayer AG’s Pigments and Ceramics Business
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