Comparison of large-and small-scale heat release tests with electrical cables

A total of 21 electrical cables were made, all with identical construction but differing in the chemical composition of their plastic components, both jacket (or sheath) and insulation. All the compounds used were commercially available materials, but they covered a variety of polymers, both halogenated and non-halogenated. All cables were tested in a large-scale cable tray test, the proposed ASTM D9.21 test, based on the IEEE 1202 or the CSA FT-4 test, modified to measure heat and smoke release in the duct and with a total length of 2.44 m. The peak rate of heat release measured served as an excellent criterion for distinguishing between cables passing and failing the test (the traditional criterion being char length). The average rate of heat released also served to distinguish the two classes of cables. Moreover, cables passing the test tended to release less smoke than those failing the test. The cables were also tested in the IEC 332-3 cable tray test. The small-scale fire test used for the cables was the cone calorimeter, ASTM E 1354. The trends observed in this heat release test were similar to those in the large-scale test. The results indicate that cables with excellent fire performance can be made by using a variety of materials, so that it would seem to follow that it is important to specify fire performance and leave material choice to manufacturers.     

Poly(vinyl chloride) and its fire properties

This work provides an up‐to‐date review of the fire properties of poly(vinyl chloride) (PVC) materials, both rigid (unplasticized) and flexible (plasticized). The fire properties addressed include ignitability, ease of extinction (oxygen index), flame spread (small scale and intermediate scale), heat release, smoke obscuration, smoke toxicity, hydrogen chloride emission and decay, and performance in real‐scale fires. This comprehensive review includes a wide selection of references and tables illustrating the properties of PVC materials in comparison with those of other polymeric materials, including, in many instances, wood materials. The work puts these fire properties in perspective, showing that the heat release rate (the key fire property) of rigid PVC (and that of properly flame‐retarded flexible PVC) are among the lower values found for combustible materials. This work also shows that the smoke toxicity and smoke obscuration resulting from burning PVC materials in real‐scale fires is in the same range as those of other materials.     

Comparison of the smoke toxicity of four vinyl wire and cable compounds using different test methods

Four vinyl wire and cable materials were tested using five smoke toxic potency test methods: the NBS cup furnace test (in its flaming and non-flaming modes), the NIST radiant test, the NIBS IT₅₀ test (also using the radiant apparatus) and the UPITT test. One of the materials is a standard poly(vinyl chloride) (PVC) flexible wire and cable material, used commercially for wire insulation. The three other materials tested represent a new family of vinyl thermoplastic elastomer alloys, which are advanced materials with good fire performance, particularly in terms of heat release and smoke obscuration. It was found that the smokes from all four materials are similar in terms of their toxic potencies, and that they are all within the ‘common’ range of toxic potency found. In particular, the toxic potencies of the smoke from the new vinyl thermoplastic elastomer alloys are not significantly different from those of other traditional vinyl wire and cable compounds. The results of the tests were also interpreted in terms of the toxicities and concentrations of the individual gases emitted. The fractional effective dose of the toxicants analysed was sufficient to account for the toxicity of the smoke for the NBS cup furnace and the NISt radiant test. It was not able to account for the toxicity found in the UPITT test. The adequacy of the test protocols themselves was also investigated. It was found that the UPITT and the NIBS IT₅₀ method are inadequate for measurement of smoke toxicity. It was also found that the NIST radiant test protocol is the one most likely to lead to the smallest amount of future testing.     

Survey of fire testing of electrical cables

The National Electrical Code (NEC) is the document which regulates electrical cables in the United States. It addresses two fire properties only for which it requires testing: flame spread and smoke obscuration. Thus, a hierarchy of tests exists which cables need to pass to be allowed in occupancies regulated by the NEC. On a flame spread basis they are, in increasing severity: UL VW-1, UL 1581, UL 1666 and UL 910. For smoke obscuration only one test is mentioned in the NEC: UL 910. The /LS category (limited smoke) introduced in NEC '90, as a voluntary label, will probably be addressed in NEC '93 under the new standard UL 1685, a modification of UL 1581. Rate of heat release is measured for cables only for R&D purposes. However, it is by now well established that rate of heat release is the one most important fire property to assess fire hazard. Cable flame spread tests (except for VW-1) have all been modified, in non-standard ways, to measure rate of heat release, which gives much more useful results than char-length determinations. Moreover, small-scale RHR test instruments (cone calorimeter, OSU calorimeter) have also been used extensively to test cables. The results of such tests have been correlated with those of UL 1581 (and of similar cable tray tests) in several cases, with excellent outcome. Work is underway to develop algorithms to predict largescale cable test results from small-scale compound tests. This area of research is very promising, and, once completed, would decrease product development costs considerably and allow faster introduction of advanced materials into the market. However, such work can only be completed by using rate of heat release techniques in both large- and small-scale tests.     

表面包覆的多金属氧酸盐在膨胀阻燃电缆材料中的抑烟作用

利用硅烷偶联剂对一种Keggin型多金属氧酸盐(十二钼磷酸盐)进行表面包覆处理,然后与膨胀阻燃(IFR)电缆材料共混制备出一种低烟阻燃复合材料,研究了表面包覆的多金属氧酸盐在该复合材料中的抑烟作用,以及对材料性能的影响。结果表明:多金属氧酸盐的引入可以一定程度上抑制材料在燃烧过程中的烟气释放,其中,添加了0.8%-3.0%包覆处理的多金属氧酸盐的IFR电缆材料,其烟密度可以降低15%;另外,该多金属氧酸盐基抑烟剂对IFR电缆材料的力学性能、阻燃性能及电性能等的影响很小。     

Rheological properties of polyvinylidene fluoride and polymethyl methacrylate engineering alloys

Recent concerns over smoke toxicity and optical properties have forced the electrical/electronics industries, particularly the wire and cable and fiber-optics industries, to focus attention on the development of new materials. The demands are critical for these applications and include not only optical and flammability properties but also thermal and mechanical properties, and, of course, processability. Acrylic-fluoroplastic alloys are exceptional candidates for meeting such requirements. Along with various optical evaluation and traditional mechanical testing, dynamic mechanical testing (DMT) procedures, as specified by ASTM protocols, can be used to evaluate, qualify, and quantify alloys for their end-use properties and processability. Specifically, this paper shows how DMT can be used to monitor both the solid and melt rheological properties of several PMMA/PVDF alloys. Important results of this study include the evaluation of compatibility/miscibility, modulus as a function of temperature, melt viscosity as a function of shear rate, and melt viscosity as a function of temperature.     

聚酰亚胺薄膜技术进展与市场前景

聚酰亚胺薄膜是目前世界上性能最好的薄膜类绝缘材料之一,具有优良的力学性能、电性能、化学稳定性以及很高的抗辐射性能及耐高温和耐低温性能,在航空航天、国防军工、新型建材、环保消防等领域中发挥着越来越重要的作用。介绍了聚酰亚胺薄膜的理化性能、制取工艺、技术进展、应用领域及市场前景,并对国内聚酰亚胺薄膜产业的发展提出了一些建议。     

低烟低卤PVC电缆料的配方设计

介绍阻燃低烟低卤聚氯乙烯(PVC)电缆料的研制,通过改变氢氧化铝(Al(OH)3)、三氧化二锑(Sb2O3)、硼酸锌(2ZnO·3B2O3·5H2O)等的用量,观察PVC电缆料的阻燃效果和发烟量的变化,并综合其力学性能和电性能的变化情况,最终确定阻燃剂的最佳组合及最佳配比。     

Fire hazards of organic materials—small scale assessment of flammability and smoke generation

The flammability and smoke generation properties of a number of organic materials used in ships, including laminated materials, rigid and flexible cellular polymers, cable insulting materials and adhesives, have been evaluated. The relative flammabilities were determined by the limiting oxygen index method that gives convenient, reproducible, numerical ratings of materials. Smoke generation was assessed photometrically by measuring light attenuation under standard conditions and is reported in terms of the total amount of smoke generated, as well as the times for the smoke density to reach an arbitrary ‘critical’ level and the maximum value. Materials with low flammability and low smoke generation characteristics have been identified, as well as those that would be hazardous in the event of a fire.     

Development of thin‐walled halogen‐free cable insulation and halogen‐free fire‐resistant low‐smoke cable‐sheathing compounds based on polyolefin elastomer and ethylene vinyl acetate blends

There is a growing interest in the use of polyolefins and their copolymer blends in cable industries. The present investigation deals with the development of thin‐walled halogen‐free cable insulation and thin‐walled halogen‐free fire‐resistant low‐smoke cable sheathing compounds based on polyolefin elastomer (Engage®) and ethylene vinyl acetate (EVA) blends. Blends of Engage (an ethylene octene copolymer) and EVA, varying in proportions, are prepared on a two‐roll mixing mill at an elevated temperature. Physicomechanical, electrical, and the most important flame‐retardant properties of the dicumyl peroxide/triallyl cyanurate cured blends have been basically studied. Properly compounded Engage‐EVA blends are found to be excellent materials in cable industry for insulation as well as for sheathing compounds. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The effect of pyrolysis and combustion temperatures on smoke density

The small-scale smoke testing apparatus now proposed as a standard in France under the designation NF–T51–073 measures the total obscuration from a stream of smoke generated from a small sample. Although like other small-scale fire tests, it is not claimed to be of relevance to real fire situations, it is possible by varying the temperature over a wide range (200–900°C) to obtain a plot of specific optical density for various materials which broadly corresponds with general experience and certain other smoke tests. The plots show that nearly all flammable substances give a rapid rise in smoke opacity in the 350–500°C region above which there is always a steep drop sometimes to smoke densities of virtually zero. Apart from one or two synthetic materials which show a very low smoke density through-out, there is no general trend as between natural and synthetic substances. Oxygen depletion which often occurs in a real fire situation has some effect on the smoke density but it is not a major one. On the other hand, in some cases reheating the smoke can have quite a dramatic effect, due very probably to further pyrolysis and combustion.     

基料对防火卷材性能的影响研究

以低密度聚乙烯（PE-LD）、三元乙丙橡胶（EPDM）、氯化聚乙烯（CPE）3种材料作为基料制备了用于钢结构保护的防火卷材,研究了其对防火卷材性能的影响。结果表明,以CPE为基料的防火卷材耐火时间最长、拉伸强度和断裂伸长率较大,表现出较好的耐火性能和拉伸性能;以EPDM为基料的防火卷材的弯曲强度和弯曲模量最小,表现出较好的柔软性;CPE与EPDM以质量比6：4复配为基料的防火卷材的膨胀倍率达到22倍,具有较好的耐火性能,且此防火卷材的拉伸强度和断裂伸长率分别为2.31 MPa、855.47 %,弯曲强度和弯曲模量分别为5.47、6.11 MPa,具有良好的力学性能;CPE与EPDM复配更适合做防火卷材的基料,有利于防火材料的膨胀阻燃。     

A comparative evaluation of a novel flame retardant, 3-(tetrabromopentadecyl)-2,4,6-tribromophenol (TBPTP) with decabromodiphenyloxide (DBDPO) for applications in LDPE- and EVA-based cable materials

Flame retardation of polymeric materials for cables is becoming a statutory requirement due to governmental regulations to protect life and property from damages caused by fire. This and other factors such as the ever-increasing cost of existing flame retardants (FRs) have given rise to the search for better FRs. In this article, the suitability of an FR, 3-(pentadecyltetrabromo)-2,4,6-tribromophenol (TBPTP) developed from cardanol was evaluated for use in cable insulating and jacketing materials based on low-density polyethylene (LDPE) and ethylene vinyl acetate (EVA). The processability, mechanical properties, compatibility and miscibility, thermal behavior, flammability behavior, smoke generation, acid emission, aging characteristics etc., of the blends of the FR with LDPE and EVA were studied in comparison to those of decabromodiphenyl oxide (DBDPO), which is a standard FR used by the cable industry. Although TBPTP is found to be less thermally stable than is DBDPO, it exhibited better flame retardancy and has comparable thermal stability when blended with LDPE and EVA. Both LDPE—TBPTP and EVA—TBPTP blends produced less smoke than did the corresponding blends of DBDPO. In the case of the EVA—TBPTP blend, the percentage emission of smoke was almost negligible, placing EVA—TBPTP under the low smoke grade. Formulations containing a synergistic agent, promoter, and filler with the corresponding FR and polymer polymer along with an antioxidant were extruded out into wire and tested for cable properties. At 20% loading, the LOI values of the blends were 34.6 and 32.5, respectively, for the TBPTP—EVA and DBDPO—EVA blends. Vertical burning tests carried out with EVA—TBPTP cable showed that it is self-extinguishable. The processability of the compositions containing TBPTP were better than those of DBDPO. The improved processability was found to be due to the plasticising effect of TBPTP. SEM pictures of the blend showed excellent distribution of TBPTP in the polymer, indicating good compatibility and miscibility. Comparatively, DBDPO did not exhibit uniform distribution. The mechanical properties of the blends were within specifications of standard cable materials except that the % elongation of the DBDPO—LDPE blend was far too low. Aging studies also gave better properties for the TBPTP system than for those of the DBDPO system. The overall results show that the properties of EVA—TBPTP cable fall within specifications for the FARLS grade, whereas the EVA—DBDPO cable did not. In the case of LDPE, both TBPTP and DBDPO did not satisfy specifications for the FRLS grade, but the data indicate that they can be used as FRs. The superiority in properties of the TBPTP system over DBDPO is explained in terms of the structure of TBPTP characterized by the distribution of the flame-retardant element, bromine, almost evenly between the aliphatic and aromatic moieties of the molecule, which can, in contrast to the fully aromatic DBDPO, provide halogen over a wide range of temperatures to the combustion zone of the decomposing polymer. Moreover, the presence of the aliphatic segment assures improved processability and compatibility. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 3057–3073, 1997     

Third International Conference on Environmentally Friendly Fire-Retardant Systems

The Third International Conference on Fire Retardancy of Polymeric Materials was held in Atlanta, Georgia, USA, on December 7–8, 1993. The conference focused upon the latest developments in zero- and lowhalogen additives and polymers used to minimize flammability, smoke, fume, and toxicity problems. This was an intensive and executive-level meeting for compounders and technical specialists using fire retardants (FR) in plastics, textiles, wire and cable, and furniture applications; business development managers who follow specialty chemical and additive markets; health, safety, insurance, and regulatory affairs managers; and materials, equipment, and testing/measurement specialists in the fire safety industry. An exhibition of fire retardant additives and instruments was arranged within the framework of the conference. The participants took this opportunity to discuss their needs with the exhibitors and to discover new sources of equipment, materials, and services.     

Flame retardancy and thermal stability of ethylene-vinyl acetate copolymer nanocomposites with alumina trihydrate and montmorillonite

The development of fire retardant for wire and cable sheathing materials has oriented toward low smoke and halogen-free flame retardant technology to achieve better safety for electrical equipment and devices and to satisfy standards. However, many polymer flame resistance materials require a very high proportion of metal hydrate filler within the polymer matrix (60 wt%) to achieve a suitable level of flame resistance, which may lead to inflexibility, poor mechanical properties and problems during compounding and processing. In this study, the alumina trihydrate (ATH) was added to montmorillonite (MMT) as the halogen-free flame retardant of ethylene-vinyl acetate (EVA) copolymer, with various ratios of EVA/ATH/MMT. The prepared nanocomposites were characterized through various techniques of XRD, tensile test, DSC analysis, TGA, LOI evaluation, and FE-SEM to explore the effects of organic modified clay (OMMT) and the layer distance on the mechanical, thermal, and flame resistance properties. In the XRD examinations, the layer-distance of MMT increased from 1.27 to 1.96 nm when polymer was added to the octadecylamine modified MMT. The best tensile strength was obtained at 3 wt% MMT. In addition, the halogen-free flame resistance grade of EVA containing 3 wt% OMMT and 47 wt% ATH revealed the best elongation and fire resistance (LOI = 28). The tensile and flame resistance properties of the nanocomposites were also significantly improved.     

Effect of environmental conditions on smoke propagation

This paper examines the influence of oxygen and environmental temperature on the generation of smoke from burning polystyrene sheet. The experimentation was performed using a Stanton Redcroft HFTA linked to a Stanton Redcroft FTB Smoke Box. The results showed that different forms of smoke were formed depending upon the environmental conditions. For example, in oxygen-enriched atmospheres and at elevated environmental temperatures, as in spacecraft fires, large smoke particles were formed with a lower level of obscuration. This phenomenon was accompanied by higher rates of burn and high fire temperatures. At lower oxygen contents, as in real-life fire conditions, close to the Critical Oxygen Index, finer smoke particles were formed which gave a higher level of obscuration. The time to maximum obscuration was comparatively long.     

高速挤出PVC通讯电缆绝缘材料

分析了国外高性能ＰＶＣ电缆料,在全部使用国产原材料和助剂的前提下,研制了高速挤出ＰＶＣ通讯电料。该料可以在很高的挤出速度下加下成薄壁电线在１０００ｍ／ｍｉｎ的速度下可长时间稳定加工,具有很好的电性能、机械性能及耐老化性能;加工时不存在口模冒烟现象,清模周期长;产品外观光滑,致密, 有光泽手感良好。     

Green Carbon Nanostructures for Functional Composite Materials

Carbon nanostructures are widely used as fillers to tailor the mechanical, thermal, barrier, and electrical properties of polymeric matrices employed for a wide range of applications. Reduced graphene oxide (rGO), a carbon nanostructure from the graphene derivatives family, has been incorporated in composite materials due to its remarkable electrical conductivity, mechanical strength capacity, and low cost. Graphene oxide (GO) is typically synthesized by the improved Hummers’ method and then chemically reduced to obtain rGO. However, the chemical reduction commonly uses toxic reducing agents, such as hydrazine, being environmentally unfriendly and limiting the final application of composites. Therefore, green chemical reducing agents and synthesis methods of carbon nanostructures should be employed. This paper reviews the state of the art regarding the green chemical reduction of graphene oxide reported in the last 3 years. Moreover, alternative graphitic nanostructures, such as carbons derived from biomass and carbon nanostructures supported on clays, are pointed as eco-friendly and sustainable carbonaceous additives to engineering polymer properties in composites. Finally, the application of these carbon nanostructures in polymer composites is briefly overviewed.     

Validation of the lumped parameter code COCOSYS against large‐scale OECD PRISME 2 fire experiments

Fire safety analysis is a major issue for nuclear power plants (NPPs) in the context of deterministic safety assessments as well as of probabilistic safety analyses. Oil reservoirs and cables represent major fire loads. Therefore, simulations of oil and cable fires are of interest for quantifying the risk of such internal hazards in NPPs. To investigate the applicability of lumped parameter (LP) modelling, validations against fire experiments are required. In this way, results obtained with the LP code COCOSYS for simulations of oil and cable fire experiments conducted in the OECD PRISME 2 Project are presented. The PRISME 2 VSP (vertical smoke propagation) tests involving oil fires in a confined and mechanically ventilated facility were used to assess the ability of the LP code to simulate smoke propagation through a horizontal opening from the fire compartment to a compartment on top of it. As it was already identified in the “International Collaborative Fire Modelling Project (ICFMP),” this type of opening might cause problems in fire simulations, particularly for zone or LP fire models. In these simulations, attention has been paid to the coupling between the fire and the surrounding environment due to the decrease of oxygen concentration. Furthermore, different cable materials have been tested in the PRISME 2 CORE (completing and repeating) test campaign. By simulating the CFS‐3 (cable fire spreading) test with confined underventilated conditions, the applicability of the COCOSYS cable fire model with input parameters deduced from open atmosphere fire tests (CORE‐2) was analysed. Results show that the applicability of a LP fire model to predict the pyrolysis rate is partly limited for both oil and cable fires, in confined environment. However, simulations with prescribed pyrolysis rates show encouraging results in good agreement with the experimental data and underline the capability of the LP code COCOSYS to simulate the interaction between the thermal hydraulics inside compartments and the fire source.     

新型炭材料的表面电接枝及其应用

电接枝技术能够对很多基底材料如碳材料、金属及其氧化物等进行表面修饰,使其具有更好的理化性质和机械性能,而重氮化电接枝修饰方法因其操作简便、可控性好、应用广泛而成为当今材科学和生物医学的一大热点。主要介绍新型炭材料如纳米金刚石、碳纳米管和石墨烯等的重氮化电接枝修饰、电接枝机制和应用,并加以比较;同时对重氮化电接枝修饰技术的应用前景做了展望。