Mortars containing wood-based fibres under thermal exposure using cone calorimeter heating

The behaviour of concrete structures under fire can be improved by adding fibers. However, relatively little is known of the details of the possible beneficial features of the fibre addition. The aim of this study was to compare the effects of different wood-based fibres on the thermal properties of a standard laboratory cement mortar at conditions of a developing fire. The cone calorimeter heating method was used, and the sample thickness and heat flux were varied (25 mm or 50 mm, 25 kWm^?2 or 50 kWm^?2) to compare test conditions. The fibres comprised chemical pulp, chemi-thermomechanical pulp, recycled fibres and viscose fibres. The fibre content in the mortar was 0.15–0.5% by weight. Temperature and mass loos measurements of oven-dried specimens (moisture content <0.1%) showed no differences between different wood-based fibre mortars and plain mortar. With increasing moisture content (about 5%), however, the presence of fibres affected the release of moisture from the fibre mortar material. With rapid heating of mortars, which have a moisture content of about 5%, local pressures are easily built up. These pressures are mainly caused by free water vaporization. The rear surface temperature measurements indicate that in mortars containing wood-based fibres (0.15–0.5% by weight) the vaporization temperatures may be 20 –25% lower than in the reference mortar. Some effects on heat transfer can also be observed due to differences in water vaporization and movement processes.     

A study of spalling behaviour of PAN fibre-reinforced concrete by thermal analysis

Comparisons are made between polypropylene (PP) fibres and polyacrylonitrile (PAN) fibres in order to relate the thermal properties of fibres with the respective fibre mortar behaviour under thermal exposure. Thermogravimetry (TG), differential scanning calorimetry (DSC) and thermochromatography (ThGC) are utilized. When a cementitious fibre mortar is being heated, several physical phenomena occur in the temperature range between 100°C and 200°C. There is a significant difference in the thermal behaviour between PP and PAN fibres. PP fibres melt at 160–170°C. The non-melting behaviour of PAN fibre together with its rapid exothermic degradation reactions at around 300°C may add risk to the spalling of fibre mortar under rapid thermal exposure.     

Oxidized (Cyclized) Polyacrylonitrile Fibres — Oxypan. A Review

Fibres made of oxidized polyacrylonitrile of the Oxypan type are an independent group of thermostable fires with a possible temperature of use of up to 300°C and slightly higher for a short time. The principles and methods of fabrication, structure, assortment, and properties of Oxypan oxidized PAN fibres are examined. Oxypan fibres, widely manufactured in different countries, are now the least expensive of all thermostable fibres. It is expedient to organize manufacture of these fibres in Russia, and the necessary equipment is available and in place.     

Catalytic initiation of polyacrylonitrile stabilization

A catalytic surface treatment of polyacrylonitrile fibres by dibutyltin dimethoxide is investigated as to its capacity to facilitate the stabilization of the fibres to produce a satisfactory carbon fibre precursor. The stabilization is based on a combination of the catalytic treatment step and of the usual thermal oxidation step which follows. The effectiveness of the surface treatment is determined through comparing physical, thermal and mechanical properties of stabilized fibres with and without catalytic pre-treatment. The results show that a 1 minute catalytic treatment shortens the usual 220°C thermal oxidation process by at least 2 hours, and that the process is applicable in particular to polyacrylonitrile fibres which are ‘slow oxidizers’ in general due to their chemical composition.     

Strength of a Carbon Fibre as a Function of the Physicomechanical Properties of the Initial Polyacrylonitrile Fibre

The almost linear dependence of the strength of carbon fibres on the structural factor of polyacrylonitrile fibres, expressed as the product of the strength of the initial PAN fibres by the square root of their elongation, was established. Excessive orientational drawing, despite attaining high strength of the PAN fibres, does not increase the strength of the carbon fibres and can decrease the realization of their strength in a plastic. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 4, pp. 42–43, July–August, 2000.     

Tensile properties of plant fibre‐polymer composites in fire

The structural performance of polymer composites reinforced with plant fibres when exposed to fire was experimentally evaluated and compared against an E‐glass fibre laminate. Fire testing under combined one‐sided radiant heating and static tensile loading revealed that flax, jute, or hemp fibre composites experience more rapid thermal softening and fail within much shorter times than the fibreglass laminate, which is indicative of vastly inferior structural performance in fire. The plant fibre composites soften and fail before the onset of thermal decomposition of the plant fibres and polymer matrix, whereas the E‐glass fibres provide the composite with superior tensile properties to higher temperatures and higher applied tensile stresses. The tensile performance of the three types of plant fibre composites in fire was not identical. When exposed to the same radiant heat flux, the flax fibre composite could withstand higher tensile stresses for longer times than the hemp and jute laminates, which showed similar performance.     

Study of the kinetics of oxidation of acrylic fibres

The kinetics of absorption of oxygen by polyacrylonitrile fibre and fibre from the copolymer of acrylonitrile and methacrylate was investigated during their thermooxidative stabilization at different temperatures and oxygen pressures. The dependence of the rate of oxidation of the fibres on the oxygen pressure in the region of low values and the absence of this dependence at high pressure was detected. Passage from one oxidation mechanism to the other for fibres of different compensation begins at a different oxygen pressure and is a function of the temperature. It was shown that the rate of oxidation of the fibres can be increased not by changing the oxygen pressure, but by increasing the total pressure in the system by addition of an inert gas whose molecules activate the oxygen molecules. A mechanism of oxidation of acrylic fibres based on concepts of the kinetics of monomolecular reactions was proposed. It was concluded that at atmospheric pressure, oxidation of acrylic fibres takes place in the kinetic region. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 1, pp. 28–31, January–February, 2000.     

Thermal behavior of bicomponent systems of polyacrylonitrile and hydrated cellulose fibres

Mixed bicomponent systems of polyacrylonitrile (PAN) and hydrated cellulose (HC) fibres are not mechanical mixtures with the additive properties of each component; their thermooxidative degradation takes place at lower temperatures than for each fibre individually, and takes place less actively and in a wider range of temperatures. When the degree of grinding of the fibres in the mixed systems is decreased, the temperature of the beginning and rate of thermooxidative degradation also increase. Increasing the concentration of HC fibre in the mixture from 15 to 50 wt. % decreases the heat effect of the first exothermic peak on the DTA curve, and this is of practical importance for conducting heat treatment of the fibres.All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated from Khimicheskie Volokna, No. 6, pp. 27–29, November–December, 1992.     

Performance of clay masonry prisms with light weight plaster exposed to standard fire exposure

Clay bricks are one of the most widely used materials in building construction due to their advantages, including local availability, ease of fabrication and cost-effectiveness. Fire is one of the dangerous hazards that can cause damage the life and property. Lightweight plasters play a vital role in insulating the masonry construction during fire accident. There is only limited data and information available on the fire performance of Clay Brick Masonry (CBM) insulated with lightweight plaster. An extensive investigation was undertaken to evaluate the residual strength properties and physical characteristics of CBM prisms exposed to elevated temperatures. CBM prisms plastered with M-sand mortar, vermiculite mortar, and perlite mortar were used for the investigation. Protected prisms were exposed to elevated temperatures following the ISO 834 standard fire curve for durations of 30 min (821°C), 60 min (925°C), 90 min (986°C), and 120 min (1029°C). Mechanical properties such as axial load carrying capacity, stress–strain behaviour, elastic modulus, and crack pattern were examined. The mechanical properties of CBM prisms were found to be highly influenced by the type of plastering, intensity, and the duration of heating. The microstructure and image analysis confirmed the effects of temperature exposure on protective plasters. Equations are proposed to determine the residual axial compressive strength and the elastic modulus of CBM. It was found that the specimens plastered with perlite mortar had better fire resistance.     

高温及升温速率对砂浆气体渗透性与孔隙率的影响

高温不仅降低砂浆的力学性能,还会对其耐久性产生重大的影响。通过高温马弗炉以3种不同升温速率(即5 ℃/min、10 ℃/min、15 ℃/min)加热砂浆至400 ℃、500 ℃、600 ℃来模拟火灾试验。通过新的试验技术(允许在围压下同时测量气体渗透性和孔隙率)研究了不同温度损伤后砂浆的气体渗透性和孔隙率以及力学性能的变化。结果表明,随着升温速率的加快以及温度的升高,砂浆气体渗透率与孔隙率逐渐增大。与未升温相比,当以15 ℃/min加热至600 ℃时,砂浆气体渗透率增加了2个数量级,孔隙率增大了1.77倍;在加卸载围压过程中,砂浆气体渗透率与孔隙率均不可逆地降低;升温速率越大,加热温度越高,砂浆气体渗透率与孔隙率对围压就越敏感。孔隙率对围压的敏感性与气体渗透率相比较小,但孔隙率对围压的敏感性证实了加卸载围压过程中裂纹不可逆闭合与孔隙不可逆破碎;当以3种升温速率加热砂浆至400 ℃、500 ℃和600 ℃时,随着升温速率的加快以及温度的升高,砂浆的抗压强度逐渐降低。     

Structural and chemical transformations in thermooxidative stabilization of copolymeric polyacrylonitrile fibres

The processes that take place during thermooxidative stabilization in copolymeric polyacrylonitrile (PAN) fibres of varying composition were examined. It was shown that the primary, or relaxation, shrinkage of PAN fibres is a function of the conditions of their fabrication and can be reduced by annealing the fibres above the glass transition temperature. The chemical transformations of PAN fibres are accompanied by structural transformations, manifested as shrinkage or elongation (flow) of the fibre. Mechanisms of deformation processes are proposed. The schemes of the chemical transformations of the structure of the fibres during their thermooxidative stabilization were examined. The direction and rate of chemical transformations of the structure of the fibres are a function of the composition of the copolymers; these parameters can be assigned and regulated by altering the conditions of spinning the fibres in the spinning bath. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 6, pp. 14–18, November–December, 1999.     

Thermal and residual mechanical profile of recycled aggregate concrete prepared with carbonated concrete aggregates after exposure to elevated temperatures

Thermal and residual mechanical performance of recycled aggregate concrete (RAC) prepared with recycled concrete aggregates (RCAs) after exposure to high temperatures has so far received less attention than that of conventional concrete prepared with natural aggregates (NAs). This study experimentally investigated thermal and residual mechanical performance of RAC prepared with different replacement percentages of non‐carbonated and carbonated RCAs after exposure to high temperatures. The residual mechanical properties, including compressive strength, modulus of elasticity, and peak strain at the maximum strength, were measured for evaluating the fire resistance of RAC. The experimental results showed that although the fire‐resistant ability of natural granite aggregates was high, thermal deterioration of the conventional concrete after exposure to 600°C, presented by thermal induced mesocracks, was more serious than that of RAC due to thermal incompatibility between NAs and mortar. Using the carbonated RCAs can reduce the width of thermal mesocrack in RAC. The residual mechanical properties of RAC after exposure to 600°C can be obviously improved by incorporating 20% to 40% of the carbonated RCAs. For the RAC made with the 100% carbonated RCAs, the ratio of residual to initial compressive strength after exposure to above 500°C was even higher than that of the conventional concrete.     

Fluoropolymer Fibres: Physicochemical Nature and Structural Dependence of their Unique Properties, Fabrication, and Use. A Review

Fluorine-containing fibre-forming polymers, fibres, and fibre materials have unique properties due to the presence of fluorine atoms. Totally fluorinated polymer materials are distinguished by the highest resistance to all kinds of chemical reagents and physically active media, low wettability by polar liquids, and other specific functional properties. In examining the physicochemical nature of the unique properties of fluoropolymer fibres and fibre materials with respect to the theory of chemical structure and D. I. Mendeleev's Periodic Table of the Elements, we found that they are due to the features of the fluorine atoms, which have the highest electronegativity of all elements, high ionization energy, high energies of bonds with carbon atoms, and simultaneously shield the molecular chain from external effects. Fibre-forming fluoropolymers, fibres, and fibre materials made from them have high resistance to external effects, biostability and bioinertness, and highly effective protective and other functional characteristics. This relates to the totally fluorinated materials PTFE, HFP, and CP-TFE-HFP to the greatest degree. Fibres and fibre materials based on totally fluorinated polymers (PTFE, HFP, CP-TFE-HFP) are placed in a special group for use in articles utilized in extreme conditions in exposure to especially aggressive media and other external active effects where the use of other kinds of fibres and fibre materials is difficult or impossible because of their low stability and rapid destruction.     

The charring rate and charring depth of bamboo scrimber exposed to a standard fire

To better understand the charring properties of bamboo scrimber, a standard fire test was conducted to examine the effect of moisture content, exposure time, and grain direction on the charring rate of bamboo scrimber. The bamboo scrimber specimens were exposed to fire on one side with furnace temperatures following the requirements of ISO 834. The experimental results indicated the charring depth decreased as moisture content increased from 6% to 18%. Due to the thermal insulation of the char layer of bamboo scrimber, the charring rate decreased non‐linearly as the fire exposure time increased from 10 to 40 minutes. The charring rate of bamboo scrimber parallel to grain was approximately 1.23 times that perpendicular to grain. The non‐linear equation to express the charring rate of bamboo scrimber with moisture content, exposure time, and grain direction was established by regression analysis of the test data. The temperature of the char front was approximately 280°C, determined by heat transfer analysis of the 3‐dimensional finite element method model. Compared with different timber species in the literature and in standards, bamboo scrimber has better fire performance and a lower charring rate.     

Defect content and nonuniformity in mechanical properties of polyacrylonitrile fibres

Conclusions Defect content and nonuniformity in mechanical properties of polyacrylonitrile fibres have been investigated in the cross section of tow and over the length of individual elementary fibres.For a generalized evaluation of defectiveness and nonuniformity in mechanical properties we have used the scale dependence of strength and histograms for strength distribution. Scale coefficients for the strength of polyacrylonitrile fibres have been determined.For rapid characterization of defectivity and nonuniformity of mechanical properties of fibres one can use the ratio of the mean strengths at two clamped lengths which differ significantly (by an order of magnitude or so).Translated from Khimicheskie Volokna, No. 1, pp. 33–34, January–February, 1989.     

Physicochemical properties of edible films from chitosan composites obtained by microwave heating

Summary  Chitosan films were prepared by casting, using microwave and dried by air convection. No scientific literature covers the use of microwave heating in the preparation of chitosan films by casting technique. Effects of heating time, molecular weight and plasticizer on structure, thermal behavior, surface, barrier properties and light transmission were investigated. Heating time showed that the microwave heating did not affect the structural composition and thermal decomposition of chitosan films. UV-vis light barrier properties, equilibrium moisture content and water vapor permeability varied significantly with the heating treatment. Surface film analysis revealed no captured differences between different heating treatments.     

Thermal and Mechanical Properties of Flax Fibres as Potential Composite Reinforcement

Scutched and hackled long flax fibres varying in retting degree, namely green, under‐retted and normally retted flax, and elementary fibres were tested for their mechanical and thermal properties. Tensile tests were performed on individual fibres and on bundles. The thermal stability is evaluated with thermogravimetric analyses (TGA) and determination of the mechanical properties after thermal exposure. For the investigated samples, no significant influence of the retting degree on tensile strength can be determined. Exposure to different temperatures results in a weight decrease and affects the mechanical properties of the fibres.     

Effect of the molecular weight of poly-para-aramids and structural changes in heat treatment on the mechanical indexes of the fibres

The mechanical indexes of fibres based on two types of poly-para-aramids were investigated as a function of their logarithmic viscosity characterizing the molecular weight. Fibres fabricated from the polymers of highest molecular weight with partial hydrolytic degradation in a medium of liquid-crystalline sulfuric acid solutions had the best breaking strength indexes. This could be due to a change in the polydispersity with respect to the molecular weight of the polymers. The increase in the rigidity of the fibres in thermal drawing caused by slight melting of the fibres at sites of contact with each other indirectly indicates the capacity for structural alterations, manifested by transient softening and sintering of elements of the supermolecular structure with elimination of microcracks, which preserves or even increases the breaking strength of the high-strength fibres. Terlon Limited Partnership; All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi, Translated fromKhimicheski evolokna, No.3, pp. 31–35, May–June, 1999.     

Interactions between coking coals and plastics during co-pyrolysis☆

Blends of three Australian coking coals and polypropylene, polystyrene, polyacrylonitrile and polyphenylene sulfide were prepared and the extent to which the blends fused on heating was monitored using proton magnetic resonance thermal analysis in order to identify interactions between them that could affect their fluidity. Different plastics had different effects. Polystyrene strongly reduced the fluidity of all of the coals, confirming previous findings. Polypropylene did not affect the fluidity of the two coking coals of lower rank. Polyphenylene sulfide reduced the fluidity of the coals at temperatures near the solidification temperature of the coals, and polyacrylonitrile appeared to increase the fluidity of the coals at temperatures near the softening temperature of the coals. The very different effects different plastics have on coal fluidity show that the interaction between plastics and coals must be carefully examined before plastics are added to coking coal blends.     

Delamination of laminated composites under the combined effect of nonuniform heating and absorbed moisture

During service exposure, composite structures may be subjected to local heating under which three‐dimensional temperature gradients may develop with temperature differences that can exceed 150°C. The different thermal expansion that is associated with such temperature gradients can generate a range of thermal stresses such as compressive thermal stresses around the periphery of the heated zone, leading potentially to delamination. In this article the combined effects of nonuniform heating and moisture in glass‐ and carbon fiber‐reinforced epoxy laminates are presented, detailing the results of the effect of moisture on the mechanical properties, the simulation experiments of nonuniform heating including in situ measurement of temperatures and strains, and a schematic model of the observed delamination by bulging. The main conclusion is that delamination damage in a form of bulging occurs only in the presence of a threshold level of moisture of about 1 wt%. This threshold level corresponds to the critical moisture content found to produce major mechanical property reduction and interlamina separation. The proposed mechanism comprises a chain of consequences induced by moisture, wherein chemical degradation of the interlamina hot region is followed by mechanical interlamina separation and bulging caused by steam pressure. POLYM. COMPOS., 26:770–777, 2005. © 2005 Society of Plastics Engineers