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  • 1.
    Krämer, Roland
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Gedde, Ulf
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    On the intumescence of ethylene-acrylate copolymers blended with chalk and silicone2007In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 92, p. 1899-1910Article in journal (Refereed)
    Abstract [en]

    The combustion and melt dripping of poly(ethylene-co-butyl acrylate) (EBA), EBA blended with polypropylene (EBA-PP) and poly(ethylene-co-methacrylic acid) (EMAA), each blended with calcium carbonate and polydimethylsiloxane, were studied. In situ measurement of the temperature gradient in the cone calorimeter were combined with infrared spectroscopy measurements on specimens withdrawn and quenched at different times of the experiment. The reactions that govern the degradation at the high heating rates met in the combustion could be determined and the gap to analytical techniques such as thermogravimetry bridged. The interplay of mechanical char integrity and heat feedback by the flame determined how much time the specimen dwells in temperature range of 300-420 °C where char expansion due to calcium salt formation is effective and thereby affects the heat release rate strongly. Vertical cone calorimeter and vertical flame testing were used to assess melt dripping and char stability under flaming combustion. Plate-plate rheological measurements proofed to be of limited use to compare the effect of different degradation atmospheres on the melt viscosity. The EMAA formulation had the most effective intumescent process with a low heat release rate and good char stability even in vertical configuration. Electron-beam irradiated EMAA specimens with different levels of cross-links were tested in the cone calorimeter in order to understand the role of cross-links for the intumescent process.

  • 2.
    Krämer, Roland
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Gedde, Ulf W.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Heat release and structural collapse of flexible polyurethane foam2010In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 95, no 6, p. 1115-1122Article in journal (Refereed)
    Abstract [en]

    Flexible polyurethane foam used in upholstered furniture remains one of the major fire hazards to date. The heat release rate of burning items made of foam depends strongly on the foam’s physical behavior, notably its collapse to a burning liquid that can result in a pool fire. In this contribution, the cone calorimeter was used to study the physical processes and to determine their influence on foam combustion over a range of external heat fluxes. The initial stage of foam collapse can be described as the propagation of a liquid pyrolysis layer through the foam sample. The rate of propagation of the liquid layer was found to depend strongly on the convective heat transfer from the flame, which simultaneously defined and depended on the sample shape. The effective heat of combustion during foam collapse and pool fire was matched to the heat release potential of the components of the foam formulation to deduce which are consumed. The proposed analysis can serve to clarify the mechanism of flame retardant action, as demonstrated for a commercial brominated-phosphorous compound.

  • 3.
    Krämer, Roland H.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Combustion dynamics and melt dripping of ethylene-acrylate copolyer composites2007Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The degradation and combustion of blends of ethylene-acryalte copolymer with calcium carbonate and silicone were studied by a combination of flammability tests, in-situ measurements and analytical experiments.

    Compounds of poly(ethylene-co-methacrylic acid) blended with precipitated calcium carbonate nanoparticles were prepared. The thermo-oxidative stability of these composites was significantly enhanced and thermal degradation led to the formation of calcium salts that stabilize the acrylic acid side group. Improved mechanical properties over micron-sized composites were obtained. The temperature dependence of the salt formation was analyzed in order to judge its relevance to combustion.

    The combustion of poly(ethylene-co-methacrylic acid), poly(ethylene-co-butylacrylate) and poly(ethylene-co-butylacrylate) with polypropylene, each blended with silicone and micron-sized chalk, was studied in the cone calorimeter. A combination of in-situ temperature measurements and analysis of degraded specimens quenched from the combustion process led to a detailed understanding of the dynamics of the materials’ intumescence. Differences in heat release for the different types of polymers can be explained and requirements for improved formulations were found. The char stability and melt viscosity of the materials were tested in a series of vertical flame and vertical cone calorimeter experiments. The scope of such measurements is discussed. The experiments were complemented with rheological and analytical measurements to explore the role of the physico-chemical degradation processes in the melt dripping.

  • 4.
    Krämer, Roland H.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Melt flow and surface stability effects on polymer flammability: A study on polystyrene, flexible polyurethane foam and polyolefin composites2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Our ability to accurately determine the flammability properties of polymers is hampered bythe erratic effects of deformation and liquid flow that occur during polymer combustion.This study aims to improve the understanding of such effects at several levels:

    The often obvious impact of melt flow on standardized flammability test methods forelectrical appliances is described to identify the need and to motivate others to worktowards an improved material characterization.

    The production of a burning degraded melt results from both, melting anddecomposition of thermoplastic polymers. The degradation of the polymer chains yieldsboth combustible volatiles that feed the flame and smaller molecules with a low viscositythat might spread to a burning pool. The molar mass is the property of the material that linksboth processes. Changes in molar mass at the surface of specimens exposed to fire‐like heatfluxes were analyzed, using polystyrene as a model thermoplastic material. Analyticalexperiments were combined with bench‐scale gasification and gasification/melt flowexperiments, in order to determine the extent of viscosity reduction by melting and bypolymer decomposition.

    A strong volume contraction to a low viscous liquid is characteristic for the combustionof flexible polyurethane foam, a low density cellular material used for cushions in furnitureand mattresses. Foam decomposition is initiated at low temperature (< 300 °C), yieldingignitable gases and leading to a fast flame spread that results in the formation of a burningliquid pool. The foam morphology changes rapidly during combustion and the impact ofthese changes on the heat release rate was analyzed. The distribution of flame heat transferled to strong variations in the burning rate, which shaped the specimen surface. The shapeof the surface affected in turn the distribution of flame heat flux, leading to an interlockingprocess. A custom‐made vertical test arrangement gave the ability to study the effect of heatfeedback from the burning liquid. Foam composites with carbon nanofibers and organicallymodified clay were prepared with the aim to eliminate liquefaction. Incorporation of anetwork of carbon nanofibers in the foam struts is demonstrated to prevent foamliquefaction and collapse.

    An approach to prevent melt‐dripping is the use of high filling levels of inorganicparticles in polyolefin cable materials and to promote reactions between the filler and thepolymer. The transition from a polymer melt to an immobile inorganic residue was studiedfor blends of acrylic copolymers of ethylene with chalk and silicone. The mechanical stabilityof the inorganic surface layer that formed during combustion was decisive for the materialsflammability properties. In‐situ thermocouple measurements and ex‐situ analysis of partiallyburned specimen surfaces were used to explain the coupling between the degradationmechanism of the polymer and the heat shield effect of the inorganic residue layer.

  • 5.
    Krämer, Roland
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Nilsson, Fritjof
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gedde, Ulf W.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The role of depolymerization in simultaneous gasification and melt flow of polystyrene.Manuscript (preprint) (Other academic)
  • 6.
    Krämer, Roland
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Raza, Mohsin Ali
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gedde, Ulf W
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Degradation of poly (ethylene-co-methacrylic acid)-calcium carbonate nanocomposites2007In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 92, no 10, p. 1795-1802Article in journal (Refereed)
    Abstract [en]

    Composites of poly(ethylene-co-methacrylic acid) with 5 mass fraction percent of precipitated calcium carbonate nanoparticles were prepared by melt extrusion on a miniature melt-blender and medium-scale production equipment. The composites consisted mostly of isolated particles. The ultimate mechanical properties of the nanocomposites were consequently largely superior to composites with micron-sized filler. The calcium carbonate particles were shown to offer a large surface area for calcium salt formation during the thermal degradation of the material. This imparted a stabilizing effect to the copolymer that was comparable to the neutralization of the methacrylic acid units with calcium ions. The rate of calcium salt formation was fast at temperatures above 350 degrees C. Stearic acid surface coatings did not interfere significantly with the calcium salt formation. The oxidative stability of the composites was further largely improved by the formation of a diffusion barrier.

  • 7. Mauro, Z.
    et al.
    Gilman, J. W.
    Szabolcs, M.
    Krämer, Roland H.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Effect of carbon nanofibers on flammability of polyurethane foams2009In: Changing times. New opportunities. Are you prepared?, 2009Conference paper (Refereed)
    Abstract [en]

    Untreated flexible polyurethane foams (PUFs) are prone to rapid fire growth due to their low density and thermal conductivity. Furthermore, the low viscosity of the decomposition products generates severe dripping that increases the fire hazard related to the combustion of PUFs. In fact, this downward flow of flaming liquid often results in a pool-fire that promotes flame propagation and boosts the rate of heat release (HRR) due to a significant increase in the burning area and to feed-back between the flame on the pool-fire and the residual foam. In this work the effect of carbon nanofibers (CNFs) on the HRR is investigated with special attention given to melt dripping phenomena. A modified cone calorimeter test has been developed for this purpose. It is shown that CNFs form an entangled fiber network which eliminates melt dripping and decreases the HRR.

  • 8.
    Olsson, Richard T.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Krämer, Roland
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lopez-Rubio, Amparo
    Torres-Giner, Sergio
    Jose Ocio, Maria
    Maria Lagaron, Jose
    Extraction of Microfibrils from Bacterial Cellulose Networks for Electrospinning of Anisotropic Biohybrid Fiber Yarns2010In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 9, p. 4201-4209Article in journal (Refereed)
    Abstract [en]

    Electrospinning of uniform biohybrid fibers with concealed cellulose microfibrils (CMF) is reported as a promising and environmentally sound concept for reinforcement of polymer nonwoven fiber systems of fine dimensions. The extraction and refinement of the high-strength crystalline microfibril bundles (15-20 nm thick) from bacterial cellulose networks is presented, as well as their morphology prior to and post electrospinning. Nanofibers composed of a poly(methyl methacrylate) (PMMA) matrix with cellulose contents reaching 20 wt % were repeatedly obtained. A high deuce of dispersion of the microfibrils was obtained for a variety of CMF contents and the aggregation of the CMF was greatly suppressed as the microfibrils were aligned and rapidly sealed inside the acrylate matrix during the continuous formation of the fibers. The limited CMF aggregation up to 7 wt % was related to a suppressed phase separation caused by the rapid solidification of the polymer solutions during spinning. The fibers' diameters decreased significantly from similar to 1.8 mu m (1 wt %) to similar to 100 nm (20 wt %) with increasing cellulose contents, resulting in CMF agglomerations and percolating architectures within the acrylate host, which was consistent with microscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) evaluations. The nominal content of cellulose in the fibers was assessed by Lorentzian profile fit assignment of the crystalline vs amorphous fractions of the fibers' X-ray diffractograms. TGA of fibers with low CMF content revealed that both CMF and PMMA showed a significantly improved thermal stability in the composite material. The biohybrid fibers were continuously aligned into an anisotropic nanocomposite yarns from a liquid support during spinning. The strategy described herein may allow for new mechanically robust nonwoven fiber systems, or be used as implemented on existing electrospun formulations that are lacking mechanical integrity. It is envisioned that the cellulose microfibrils may be of importance in biomedical applications where biocompatibility is a requirement.

  • 9. Zammarano, Mauro
    et al.
    Krämer, Roland H
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Harris, Jr
    Ohlemiller, J
    Shields, R
    Rahatekar, S
    Lacerda, Silvia
    Gilman, W
    Flammability reduction of flexible polyurethane foams via carbon nanofiber network formation2008In: Polymers for Advanced Technologies, ISSN 1042-7147, E-ISSN 1099-1581, Vol. 19, no 6, p. 588-595Article in journal (Refereed)
    Abstract [en]

    Untreated polyurethane flexible foams (PUFs) are prone to rapid fire growth due to their low density and low thermal conductivity. Furthermore, the low viscosity of the decomposition products generates severe dripping that increases the fire hazard related to the combustion of PUFs. In fact, this downward flow of flaming liquid often results in a pool-fire that promotes flame propagation and boosts the rate of heat release (HRR) due to a significant increase in the burning area and to feed-back between the flame on the pool-fire and the residual foam. In this work the effect of nartoparticles, i.e., clays and carbon nanofibers (CNFs), on the HRR is investigated with special attention given to melt dripping. A modified cone calorimeter test has been developed for this purpose. It is shown that CNFs form an entangled fiber network which eliminates melt dripping and decreases the HRR.

1 - 9 of 9
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