73 research outputs found
Development and characterisation of flame retardant nanoparticulate bio-based polymer composites
PhDSince the discovery of carbon nanotubes (CNTs) and nanoclays, there has been a
great deal of research conducted for uses in applications such as: energy storage,
molecular electronics, structural composites, biomedical to name but a few. Owing to
their unique intrinsic properties and size means that they have an ever growing
potential in the consumer and high technology sectors. In recent years the concept of
using these as fillers in polymers has shown great potential. One such function is, as
flame retardant additives. These possess much better environmental credentials than
halogenated based additives as well as only needing to use a small loading content
compared to traditional micron sized fillers. The combination of the above make
these fillers ideal candidates for polymers and their composites. Especially with
regards to natural fibre composites.
Owing to environmental awareness and economical considerations, natural fibre
reinforced polymer composites seem to present a viable alternative to synthetic fibre
reinforced polymer composites such as glass fibres. However, merely substituting
synthetic with natural fibres only solves part of the problem. Therefore selecting a
suitable material for the matrix is key. Cellulose is both the most common
biopolymer and the most common organic compound on Earth. About 33 % of all
plant matter is cellulose; i.e. the cellulose content of cotton is 90 % and that of wood
is 50 %. However just like their synthetic counterparts, the poor flame retardancy of
bio-derived versions restricts its application and development in important fields
such as construction and transportation.
Abstract
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Traditional methods to improve the flame retardancy of polymeric material involve
the use of the micron sized inorganic fillers like ammonium polyphosphate (APP) or
aluminium trihydroxide (ATH). Imparting flame retardancy with these inorganic
fillers is possible but only with relatively high loadings of more than 50 wt. %. This
causes detrimental effects to the mechanical properties of the composite and
embrittlement. Applying nanofillers can achieve similar if not better flame retarding
performances to their micron sized counterparts but at much lower loading levels
(<10 wt.%), thus preserving better the characteristics of the unfilled polymer such as
good flow, toughness, surface finish and low density. This is the main focus of this
study and it will be achieved by using various experimental techniques including the
cone calorimeter and the newly developed microcalorimeter.
After a comprehensive literature survey (Chapter 2), the experimental part of the
thesis starts with a feasibility study of a flame retardant natural reinforced fibre sheet
moulding compound (SMC) (Chapter 3). This work demonstrated that with a
suitable flame retardant the peak heat release rate can be reduced. Chapter 4 deals
with further improving the flame retardancy of the previously used unsaturated
polyester resin. The aim is to study any synergistic behaviour by using aluminium
trihydroxide in conjunction with ammonium polyphosphate whilst testing in the cone
calorimeter. In Chapter 5, nanofillers are used to replace traditional micron sized
fillers. In unsaturated polyester, multi-walled carbon nanotubes and sepiolite
nanoclay are used together to create a ternary polymer nanocomposite. The
microcalorimeter was employed for screening of the heat release rate. This work
showed that the ternary nanocomposite showed synergistic behaviour with regards to
significantly reducing the peak heat release rate.
Abstract
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The same nanofillers were utilised in Chapters 6 and 7 but this time in combination
with a thermoplastic (polypropylene) and bio-derived polymer (polylactic acid),
respectively. In both systems an improved flame retardancy behavior was achieved
whist meeting the recyclability objective. Chapter 8 attempts to show how the
optimised natural fibre composite would behaviour in a large scale fire test. The
ConeTools software package was used to simulate the single burning item test (SBI)
and to classify the end product. This is a necessity with regards to commercialising
the product for consumer usage. Finally, Chapter 9 is a summary of the work carried
out in this research as well as possible future work that should be conducted
Influence of fillers on mechanical properties of ATH filled EPDM during ageing by gamma irradiation
International audienceThe presence of a significant content of fillers accelerates the degradation of ATH filled EPDM subjected to gamma irradiation at room temperature. Above the melting temperature of the EPDM, this induces a decrease in the apparent mechanical reinforcement of the fillers. This also promotes de-cohesion mechanisms which leads to an increase in the strain at break with irradiation dose. It is not clear whether the use of a filler treatment attenuates this accelerating effect or not; however, part of this treatment remains efficient at a high dose and seems also to delay but not suppress the occurrence of de-cohesion mechanisms at large strain. Moreover, at room temperature, i.e. below the melting temperature, all the consequences of ageing by gamma irradiation are strongly attenuated by the presence of a semicrystalline microstructure, the morphology of which is not too strongly modified by irradiation. (C) 2010 Elsevier Ltd. All rights reserved
The Thirteenth Annual Conference YUCOMAT 2011: Programme and the Book of Abstracts
The First Conference on materials science and engineering, including physics, physical chemistry, condensed matter chemistry, and technology in general, was held in September 1995, in Herceg Novi. An initiative to establish Yugoslav Materials Research Society was born at the conference and, similar to other MR societies in the world, the programme was made and objectives determined. The Yugoslav Materials Research Society (Yu-MRS), a nongovernment and non-profit scientific association, was founded in 1997 to promote multidisciplinary goal-oriented research in materials science and engineering. The main task and objective of the Society has been to encourage creativity in materials research and engineering to reach a harmonic coordination between achievements in this field in our country and analogous activities in the world with an aim to include our country into global international projects.
Until 2003, Conferences were held every second year and then they grew into Annual Conferences that were traditionally held in Herceg Novi in September of every year. In 2007 Yu-MRS formed two new MRS: MRS-Serbia (official successor of Yu-MRS) and MRS-Montenegro (in founding). In 2008, MRS – Serbia became a member of FEMS (Federation of European Materials Societies)
Novel functionalized polyolefins as compatibilizers in polyolefin/polyamide 6 blends and polyethylene/metal hydroxide composites
Ricinoloxazoline maleinate (OXA) was grafted by melt free radical grafting onto polyolefins and elastomers to produce new compatibilizers for polymer blends. Effects of initial monomer and peroxide concentrations on the degree of grafting, on the amount of residual monomer, and on the side reactions were investigated. Reactive compatibilizers could be prepared with a suitable choice of processing conditions and initial concentrations. These oxazoline functionalized polyolefins and elastomers were found to act as effective compatibilizers in polymer blends.
Blends of polyolefins and polyamide 6 were compatibilized with two novel types of compatibilizers: oxazoline functionalized polymers prepared by grafting and functionalized polyolefins prepared by copolymerization using metallocene catalysts. Comparison was made with commercial compatibilizers. Effects of the compatibilizers on blend morphology and thermal, tensile, and impact properties were studied. All of the functionalized polyolefins were effective compatibilizers in polyethylene/polyamide 6 blends. They were able to reduce the particle size and attach the particles more firmly to the matrix. The toughness was improved, though usually at the cost of stiffness. Only functionalized polyethylenes prepared with metallocene catalysts were able to improve the stiffness and strength along with toughness.
In commercial polyolefin composites, fillers are usually coated with a fatty acid to make them organophilic. Replacement of fatty acid coatings with polymeric compatibilizers was studied in polyethylene/aluminum hydroxide (PE/ATH) and polyethylene/magnesium hydroxide (PE/MH) composites. The polymeric compatibilizers were oxazoline grafted polyethylene prepared by melt free radical grafting, hydroxyl and carboxylic acid functionalized polyethylenes prepared with metallocene catalysts, and commercial functionalized polyethylenes. Adhesion fracture changed to cohesion failure when the fatty acid coating was replaced through the addition of polymeric compatibilizers. Improvement in both stiffness and toughness was achieved, and improvements in flammability properties achieved with ATH or MH were preserved when polymeric compatibilizers were used as adhesion promoters.reviewe
Thermooxidative stability of PMMA composites
Tato práce se zabývá studiem termooxidační stability kompozitů polymethylmethakrylátu (PMMA) plněného mikro a nanočásticemi siliky. V připravených vzorcích byly použity různé objemové zlomky a různé velikosti částic siliky. Studium stability bylo prováděno pomocí termogravimetrie, která umožňuje simulovat podmínky termooxidační degradace. Indukční perioda byla stanovena za použití různých rychlostí ohřevu a aplikací izokonverzních metod. Závislosti teplot degradací na rychlostech ohřevu sloužily pro určení parametrů odvozených ze čtyř různých teplotních funkcí, které dovolují předpověď stability materiálu (indukční periody) při zvoleném rozsahu teplot. Zjištěné výsledky ukazují, že větší částice siliky snižuji stabilitu PMMA, zatímco nanočástice v nízkých koncentracích ji nijak neovlivňují.In this work the thermooxidative stability of poly(methyl metacrylate) (PMMA) composites reinforced with silica micro and nanoparticles was studied. Different volume fractions and particles sizes of silica particles were used. PMMA/silica composites were analysed by thermogravimetry which simulated the conditions of thermooxidative degradation. The induction periods were determined using different heating rates and applying the isoconversional methods. The dependence of degradation temperatures on heating rates were used for the determination of adjustable parameters derived for four different temperature functions allowing the prediction of material stability (induction periods) at chosen temperatures. Results showed that the larger silica particles destabilized the PMMA structure while smallest nanoparticles at low concentration had no effect on the stability.
Advanced Flame Retardant Materials
Recent disasters caused by the spread of fire in buildings and in transportations remind us of the importance of fire protection. Using flame-retardant materials is one important element of the firefighting strategy, which aims to prevent fire development and propagation. These materials are used in different applications, such as in textiles, coatings, foams, furniture, and cables. The development of more efficient and environmentally friendly flame-retardant additives is an active multidisciplinary approach that has attracted a great deal of interest. Studies have aimed at the development of new, sustainable, and flame-retardant additives/materials, providing high performance and low toxicity. Also studied were their properties during ageing and recycling, as well as modeling physical and chemical processes occuring before ignition and during their combustion. The development of sustainable flame retardants and understanding their modes of action provide a strong link between these topics and cover many fields from organic chemistry, materials engineering, and toxicology, to physics and mathematics
Flame Retardant Polymer Nanocomposites and Interfaces
The flame retardant efficiency of polymer nanocomposites is highly dependent on the dispersion of the nano-fillers within the polymer matrix. In order to control the filler dispersion, it is very essential to explore the interfacial compatibility between fillers and matrices, which provides a guide for the flame retardant nanocomposites compounding. In this short review, we mainly focus on the thermoplastic polymers and their interactions with the surfaces of the flame retardant fillers. Other physical properties of those nanocomposites such as mechanical properties, gas permeability, rheological performance and thermal conductivity are also briefly reviewed along with the flame retardancy, since they are all dispersion related
Mg-Al Layered Double Hydroxide: A Potential Nanofiller and Flame-Retardant for Polyethylene
The presented research report deals with the investigation of magnesium aluminum based layered double hydroxide (LDH) as a potential nanofiller and flame-retardant for polymers with special reference to polyethylene. LDH is a mixed hydroxide of di- and trivalent metal ions that crystallizes in the form of mineral brucite. The basic reason for selecting LDH or more specifically magnesium-aluminum based LDH (Mg-Al LDH) is their typical metal hydroxide-like chemistry and conventional clay-like layered crystalline structure. The former is helpful in the direct participation in flame inhibition through endothermic decomposition and stable char formation. On the other hand, the later makes LDH suitable for polymer nanocomposite preparation, which can address the poor dispersibility problem associated with conventional metal hydroxide type fillers in polyolefin matrix. Besides, unlike layered silicate type clays (often reported for their capability to improve flame retardancy of polymers), LDH being reactive during combustion has higher efficiency to reduce the heat released during combustion of the composites. LDH clay with fixed Al:Mg ratio was synthesized using urea hydrolysis method and characterized. The organic modification of Mg-Al LDH using anionic surfactants has been studied in details. The main purpose of such modification is to enlarge the interlayer distance and to render it more organophilic. The surfactants were selected based on their functionality, chain length, etc and the modification was carried out by regeneration method. In the modified LDHs, the surfactants anions are arranged as a monolayer in the interlayer region and expand the interlayer distance according to their tail size. PE/LDH nanocomposites were prepared by melt-compounding method using a co-rotating tightly intermeshed twin-screw extruder and the morphological, mechanical and flammability properties of the nanocomposites were investigated in details. The X-ray diffraction analysis and electron microscopic analysis show a complex LDH particle morphology with hierarchy of particle size and shape starting from exfoliated particles fragments to particle aggregates over few hundred nm size. The exfoliated LDH platelets are distributed both in the vicinity of large particles and also in the bulk matrix. The melt rheological characterization of the nanocomposites also reflects the similar complex particle morphology. The dynamic oscillatory shear experiments showed that with increasing LDH concentration, the rheological behavior of the nanocomposite melts deviates strongly from that of the unfilled polyethylene. Thermogravimetric analysis (TGA) shows that LDH significantly improves the thermal stability of the polymer matrix in comparison to the unfilled polymer. The flammability studies of the PE/LDH nanocomposites have been reported in terms of various standard methods, like limited oxygen index (LOI), cone-calorimetry and UL-94 vertical and horizontal burn tests. The cone-calorimetric investigation shows that the nanocomposites have significantly lower burning rate and heat released during combustion. With increasing concentration of LDH though the LOI value of the nanocomposite increases marginally, the burning behavior, like dripping, rate of burning, etc are significantly improved. The flammability performance of LDH in combination with other commonly used flame-retardant (magnesium hydroxide) was also investigated. It has been observed that in polyethylene, a 50 wt% combination filler (4:1 weight ratio of magnesium hydroxide and LDH) can provide similar flammability ratings (like V0 rating in UL94 test, no dripping, etc) as that observed with 60 wt% magnesium hydroxide alone
Multi-scale Fire Modelling of Combustible Building Materials
The utilisation of lightweight polymers in building materials has come under tremendous scrutiny, driven by the numerous high-profile fire incidents (e.g., Grenfell Tower UK, 2017) and heightened public awareness of highly combustible materials in the past decade. Consequently, this creates significant interest in developing robust numerical tools to effectively assess the fire behaviours and toxicity of these combustible materials and establish safe use guidelines. In this dissertation, a modelling framework has been developed incorporating multi-scale computational techniques that capture and couple the thermal degradation and combustion characteristics of building materials. This includes (i) characterisation of essential pyrolysis kinetics from thermogravimetric analysis (TGA) via machine learning aided algorithm; (ii) in-depth pyrolysis breakdown from molecular dynamics (MD) simulations coupled with reactive force fields (ReaxFF); and (iii) Computational Fluid Dynamics (CFD) pyrolysis model involving char formation, moving boundary surface tracking and gas-phase combustion considering detailed chemical reaction mechanisms and soot particle formation.
The framework was adopted to assess the fire performance of a selection of FR/non-FR building materials. For the first time, the composition of char formations for the selective polymers was predicted by the MD simulation by analysing the accumulation of pure carbon chain compounds. The extracted pyrolysis kinetics achieved accurate fits with the experimental data. Furthermore, the application of MD allowed the characterisation of the full distribution of volatile and toxic gas species without substantial prior knowledge or experimental testing. The realised pyrolysis inputs were applied in the CFD model for cone calorimeter simulations, which yielded good agreement with experiments in terms of heat release, ignition time and burning duration. With the incorporation of solid interface tracking and char formation, the model was able to predict the thermal degrading solid surface and capture the prolonged burn duration. The char formation acts as a thermal layer to protect the unburnt virgin material from heat penetration during the pyrolysis process. Furthermore, with the application of detailed chemical kinetics for combustion and soot formation reaction mechanisms, the fire model was able to aptly predict the generation of asphyxiant gas such as CO and CO2 during the burning process
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