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The role of depolymerization in simultaneous gasification and melt flow of polystyrene.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-14215OAI: oai:DiVA.org:kth-14215DiVA: diva2:331782
Note
QC 20100726Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2012-04-23Bibliographically approved
In thesis
1. Melt flow and surface stability effects on polymer flammability: A study on polystyrene, flexible polyurethane foam and polyolefin composites
Open this publication in new window or tab >>Melt flow and surface stability effects on polymer flammability: A study on polystyrene, flexible polyurethane foam and polyolefin composites
2009 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 60 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:5
Keyword
Melt, flow, dripping, collapse, combustion, pool fire, feed‐back, gasification, heat release, flammability, nanocomposites, molar mass, intumescence, polyurethane
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-10079 (URN)978-91-7415-239-5 (ISBN)
Public defence
2009-03-20, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100726Available from: 2009-03-11 Created: 2009-03-11 Last updated: 2010-07-26Bibliographically approved
2. Simulations of Semi-Crystalline Polymers and Polymer Composites in order to predict Electrical, Thermal, Mechanical and Diffusion Properties
Open this publication in new window or tab >>Simulations of Semi-Crystalline Polymers and Polymer Composites in order to predict Electrical, Thermal, Mechanical and Diffusion Properties
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Several novel computer simulation models were developed for predicting electrical, mechanical, thermal and diffusion properties of materials with complex microstructures, such as composites, semi-crystalline polymers and foams.

A Monte Carlo model for simulating solvent diffusion through spherulitic semicrystalline polyethylene was developed. The spherulite model, based on findings by electron microscopy, could mimic polyethylenes with crystallinities up to 64 wt%. Due to the dendritic structure of the spherulites, the diffusion was surprisingly independent of the aspect ratio of the individual crystals. A correlation was found between the geometrical impedance factor (τ) and the average free path length of the penetrant molecules in the amorphous phase. A new relationship was found between volume crystallinity and τ. The equation was confirmed with experimental diffusivity data for Ar, CH4, N2 and n-hexane in polyethylene.

For electrostatics, a novel analytical mixing model was formulated to predict the effective dielectric permittivity of 2- and 3-component composites. Results obtained with the model showed a clearly better agreement with corresponding finite element data than previous models. The analytical 3-component equation was in accordance with experimental data for nanocomposites based on mica/polyimide and epoxy/ hollow glass sphere composites. Two finite element models for composite electrostatics were developed.

It is generally recognized that the fracture toughness and the slow crack growth of semicrystalline polymers depend on the concentrations of tie chains and trapped entanglements bridging adjacent crystal layers in the polymer. A Monte Carlo simulation method for calculating these properties was developed. The simulations revealed that the concentration of trapped entanglements is substantial and probably has a major impact on the stress transfer between crystals. The simulations were in accordance with experimental rubber modulus data.

A finite element model (FEM) including diffusion and heat transfer was developed for determining the concentration of gases/solutes in polymers. As part of the FEM model, two accurate pressure-volume-temperature (PVT) relations were developed. To predict solubility, the current "state of the art" model NELF was improved by including the PVT models and by including chemical interactions using the Hansen solubility parameters. To predict diffusivity, a novel free-volume diffusion model was derived based on group contribution methods. All the models were used without adjustable parameters and gave results in agreement with experimental data, including recent data obtained for polycarbonate and poly(ether-etherketone) pressurized with nitrogen at 67 MPa.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:15
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-93519 (URN)978-91-7501-290-2 (ISBN)
Public defence
2012-04-20, F2,, Lindstedtsvägen 28, entréplan, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120420Available from: 2012-04-20 Created: 2012-04-20 Last updated: 2012-04-23Bibliographically approved

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