Advanced

Foam, Fire and Free Volume - Chemical and Physical Aspects of Porous Polymers

Andersson, Anna LU (2010)
Abstract (Swedish)
Popular Abstract in Swedish

Bilsäten har genomgått en kontinuerlig utveckling ända sedan de först beskrevs år 1885. På den tiden kunde man läsa om vadderade läderbänkar, monterade på stora fjädrar, fastsatta i chassit på ”hästlösa vagnar”. När polyuretanskum först började tillverkas på 1950-talet introducerades de snabbt i bilsätena och dessa genomgick stora förbättringar. Skummen utgör idag en stor del av interiören i våra bilar och de bildar förarens och passagerarnas kontaktyta mot själva bilen. Dessa material måste därför uppfylla flera viktiga krav på säkerhet och komfort.

I studien som presenteras här har flera aspekter av polyuretanskummens egenskaper studerats. Särskilt fokus har lagts på brandskyddande,... (More)
Popular Abstract in Swedish

Bilsäten har genomgått en kontinuerlig utveckling ända sedan de först beskrevs år 1885. På den tiden kunde man läsa om vadderade läderbänkar, monterade på stora fjädrar, fastsatta i chassit på ”hästlösa vagnar”. När polyuretanskum först började tillverkas på 1950-talet introducerades de snabbt i bilsätena och dessa genomgick stora förbättringar. Skummen utgör idag en stor del av interiören i våra bilar och de bildar förarens och passagerarnas kontaktyta mot själva bilen. Dessa material måste därför uppfylla flera viktiga krav på säkerhet och komfort.

I studien som presenteras här har flera aspekter av polyuretanskummens egenskaper studerats. Särskilt fokus har lagts på brandskyddande, mekaniska och vibrations-dämpande egenskaper. Det visade sig att de skum som används i bilsäten kan brandskyddas genom att tillsätta så kallade intumescenta komponenter (från latinets intumescere, som betyder att svälla). Intumescenta komponenter är sådana som reagerar med varandra och sväller när de utsätts för värme. Tekniken är känd från utvecklingen av intumescenta färger som sväller och skyddar det underliggande materialet mot hastig temperaturstegring vid brand. Den intumescenta processen verkar brandhämmande och värmeutvecklingen under brand minskade avsevärt när det intumescenta systemet var tillsatt till skummet. Dessutom fanns ett karakteristiskt lager av förkolnat material kvar efter brandtestet, vilket tyder på att den intumescenta processen hade verkat.

En ny, lovande metod för att förbättra de mekaniska egenskaperna i polyuretan-skum, utan att samtidigt öka densiteten på skummen, är att tillsätta hyperförgrenade polymerer. Dessa polymerer har en kärna med fyra armar, varje arm är i sin tur förgrenad så att hela molekylen har mängder med grenar. Denna hyperförgrenade polymer tillsattes polyuretanskummen i låga halter och visade sig ha stor positiv effekt på de mekaniska egenskaperna. Parallellt med förbättrade mekaniska egenskaper bidrog den hyperförgrenade polymeren, om än lite, med vibrations-dämpande egenskaper i intervallet kring 1 Hz. När frekvensintervallet utökades till det hörande området, 100-5000 Hz, visade det sig att materialets ljudabsorption ökade som funktion av mängden hyperförgrenad polymer i ett intervall mellan 500 Hz och 1600 Hz. För att utreda hur den hyperförgrenade molekylen kunde bidra till akustisk dämpning studerades materialets kemiska egenskaper med infraröd spektroskopi, en metod som avslöjar vilka kemiska bindningar och grupper som finns i ett material. Det kunde fastsällas att den hyperförgrenade polymeren var fullständigt reagerad med polyuretanen och fungerade som en effektiv tvärbindare i systemet. Samtidigt minskade mängden vätebindningar till följd av den ökade tvärbindningsgraden.

Superkritisk koldioxid (scCO2) är koldioxid som värmts till över 31 °C och trycksatts till över 7.4 MPa. Vid detta tillstånd beter sig ämnet som ett mellanting mellan en gas och en vätska, det har gasliknande viskositet men vätskeliknande densitet. Inom ramen för denna studie har scCO2 använts som medel för att genomföra kristallisation och kristallövergångar i polymerer. För att en polymer ska kunna ordna sina långa kedjor regelbundet och bilda kristaller krävs en viss rörlighet hos kedjesegmenten. Denna rörlighet är relaterad till polymerens fria volym. Den fria volymen är den volym i de amorfa (icke-kristallina) delarna av polymeren som inte utgörs av polymerkedjorna, det vill säga utrymmet mellan kedjorna. Storleken på dessa hålrum är oftast mindre än en nanometer och kan erhållas genom att mäta livslängden på elektronens antimateria, positronen, med en metod som kallas PALS. Polymerer som behandlades i scCO2 svällde och uppvisade större storlek på den fria volymen än de obehandlade polymererna. Tiden som polymeren behandlades, och vid vilken temperatur, påverkade kristallisationen av polymeren men inte storleken på den fria volymen. Däremot hade trycket under behandlingen stor inverkan på den fria volymen. Större tryck gav större storlek på den fria volymen hos den behandlade polymeren. Den expanderade fria volymen var märkbar även flera veckor efter scCO2-behandlingen vilket visar på en långvarig effekt av behandlingen. (Less)
Abstract
Automotive seating has been under continous development since it was described for the first time in 1885. At that time one could read about a “padded leather bench seat sitting on springs mounted directly to the frame of a horse-less carriage”. With the development of flexible polyurethane foam in 1950-1960 the seats were considerably improved and the traditional springs were eventually replaced by foams throughout the seat. Flexible polyurethane foam constitutes a large part of the interiour of our vehicles and it represents the interphase between the driver/passanger and the vehicle, therefore it needs to meet up to several requrements coupled to safety and comfort of driving.



In this study several aspects of flexible... (More)
Automotive seating has been under continous development since it was described for the first time in 1885. At that time one could read about a “padded leather bench seat sitting on springs mounted directly to the frame of a horse-less carriage”. With the development of flexible polyurethane foam in 1950-1960 the seats were considerably improved and the traditional springs were eventually replaced by foams throughout the seat. Flexible polyurethane foam constitutes a large part of the interiour of our vehicles and it represents the interphase between the driver/passanger and the vehicle, therefore it needs to meet up to several requrements coupled to safety and comfort of driving.



In this study several aspects of flexible polyurethane foams have been investigated. Specific focus has been on flame retardancy, mechanical properties and noise reduction. It was found that an intumescent system – a flame retardant system which swells when subjected to heat – containing ammonium polyphosphate, pentaerythritol and melamine could be incorporated to a loading of 7.5 % in a flexible polyurethane foam formulation. This novel flame retarded material showed significantly reduced values of heat release measured with cone calorimetry. There was furthermore evidence of char formation after the cone calorimetry measurement, indicating that intumescence occurred to some degree. Characterization of mechanical properties of flexible polyurethane foams are in general well developed in tensile and compression modes. In the present study we expanded the view on automovtive foams by looking at the shear behaviour of flexible polyurethane foams under uniaxial compressive deformation. The foams were found to exhibit negative apparent Poisson ratios at a certain uniaxial deformation window. A promising, alternative route to increased load bearing in flexible polyurethane foams was investigated. Small additions of a hyperbranched polymer (HBP) enhanced the load bearing properties considerably parallel to a small but significant increase of damping at 1 Hz. The addition of HBP furthermore affected the sound absorption of flexible polyurethane foam. In a region between 500 and 1600 Hz the normal incident sound absorption coefficient alfa increased systematically with HBP loading. The chemical nature of the strut material was investigated to gain knowledge in mechanism behind the sound absorption enhancement, since no morphological differences in cell structure could be detected among the foams. Solvent extraction and FTIR analysis confirmed incorporation of HBP into the polymer backbone by reaction with isocyanate.



Supercritical carbon dioxide scCO2 offers an environmental friendly and inexpensive approach to solvent treatment of polymers. The supercritical state of CO2 is reached at temperatures above 31 °C and pressures above 7.4 MPa At these conditions the compound exhibits properties intermediate of a gas and a liquid, with gas-like viscosity and liquid-like density. The scCO2 plasticizes and swells the polymer, inducing crystallization and certain crystal transitions.



In the present study positron annihilation lifetime spectroscopy (PALS) was utilized to investigate the scCO2 treatment effect on free volume of semi-crystalline polymers. Supercritical CO2 treatment resulted in an increased size of the free volume sites of syndiotactic polystyrene and poly(ethylene naphthalate). Among the treatment parameters time, temperature and pressure, only pressure had a significant effect on the value of free volume expansion. Treatment pressure as well as temperature affected the crystallization and crystal transitions taking place during the scCO2 treatment. Crystal transitions not feasible at ambient conditions, e.g. gamma-crystalline sPS into the beta-form, were performed in scCO2. The expanded free volume, which is coupled to the amorphous fraction of the polymer, was observed several weeks after treatment, long after the gas had desorbed from the material, indicating a long-term effect caused by the scCO2 treatment. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof Gedde, Ulf W, Fibre and Polymer Technology, KTH, Stockholm
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Poisson ratio, vibration damping, acoustic impedance, cell morphology, hyperbranched polymer, Polymer foams, free volume, positron annihilation, supercritical fluid.
defense location
Lecture hall B, Centre for Chemistry and Chemical Engineering, Getingevägen 60, Lund University Faculty of Engineering
defense date
2010-09-17 13:00
ISBN
978-91-7422-245-6
language
English
LU publication?
yes
id
2aea570e-462b-4568-a3a8-f24a14d0222c (old id 1658739)
date added to LUP
2010-08-23 15:27:00
date last changed
2016-09-19 08:45:19
@misc{2aea570e-462b-4568-a3a8-f24a14d0222c,
  abstract     = {Automotive seating has been under continous development since it was described for the first time in 1885. At that time one could read about a “padded leather bench seat sitting on springs mounted directly to the frame of a horse-less carriage”. With the development of flexible polyurethane foam in 1950-1960 the seats were considerably improved and the traditional springs were eventually replaced by foams throughout the seat. Flexible polyurethane foam constitutes a large part of the interiour of our vehicles and it represents the interphase between the driver/passanger and the vehicle, therefore it needs to meet up to several requrements coupled to safety and comfort of driving.<br/><br>
<br/><br>
In this study several aspects of flexible polyurethane foams have been investigated. Specific focus has been on flame retardancy, mechanical properties and noise reduction. It was found that an intumescent system – a flame retardant system which swells when subjected to heat – containing ammonium polyphosphate, pentaerythritol and melamine could be incorporated to a loading of 7.5 % in a flexible polyurethane foam formulation. This novel flame retarded material showed significantly reduced values of heat release measured with cone calorimetry. There was furthermore evidence of char formation after the cone calorimetry measurement, indicating that intumescence occurred to some degree. Characterization of mechanical properties of flexible polyurethane foams are in general well developed in tensile and compression modes. In the present study we expanded the view on automovtive foams by looking at the shear behaviour of flexible polyurethane foams under uniaxial compressive deformation. The foams were found to exhibit negative apparent Poisson ratios at a certain uniaxial deformation window. A promising, alternative route to increased load bearing in flexible polyurethane foams was investigated. Small additions of a hyperbranched polymer (HBP) enhanced the load bearing properties considerably parallel to a small but significant increase of damping at 1 Hz. The addition of HBP furthermore affected the sound absorption of flexible polyurethane foam. In a region between 500 and 1600 Hz the normal incident sound absorption coefficient alfa increased systematically with HBP loading. The chemical nature of the strut material was investigated to gain knowledge in mechanism behind the sound absorption enhancement, since no morphological differences in cell structure could be detected among the foams. Solvent extraction and FTIR analysis confirmed incorporation of HBP into the polymer backbone by reaction with isocyanate.<br/><br>
<br/><br>
Supercritical carbon dioxide scCO2 offers an environmental friendly and inexpensive approach to solvent treatment of polymers. The supercritical state of CO2 is reached at temperatures above 31 °C and pressures above 7.4 MPa At these conditions the compound exhibits properties intermediate of a gas and a liquid, with gas-like viscosity and liquid-like density. The scCO2 plasticizes and swells the polymer, inducing crystallization and certain crystal transitions.<br/><br>
<br/><br>
In the present study positron annihilation lifetime spectroscopy (PALS) was utilized to investigate the scCO2 treatment effect on free volume of semi-crystalline polymers. Supercritical CO2 treatment resulted in an increased size of the free volume sites of syndiotactic polystyrene and poly(ethylene naphthalate). Among the treatment parameters time, temperature and pressure, only pressure had a significant effect on the value of free volume expansion. Treatment pressure as well as temperature affected the crystallization and crystal transitions taking place during the scCO2 treatment. Crystal transitions not feasible at ambient conditions, e.g. gamma-crystalline sPS into the beta-form, were performed in scCO2. The expanded free volume, which is coupled to the amorphous fraction of the polymer, was observed several weeks after treatment, long after the gas had desorbed from the material, indicating a long-term effect caused by the scCO2 treatment.},
  author       = {Andersson, Anna},
  isbn         = {978-91-7422-245-6},
  keyword      = {Poisson ratio,vibration damping,acoustic impedance,cell morphology,hyperbranched polymer,Polymer foams,free volume,positron annihilation,supercritical fluid.},
  language     = {eng},
  title        = {Foam, Fire and Free Volume - Chemical and Physical Aspects of Porous Polymers},
  year         = {2010},
}