Vnetljivost polimernih kompozitov z ogljikovimi vlakni

diplomsko delo

Luka Skubic (Avtor), Urška Šebenik (Mentor)

Povzetek

Ogljikova vlakna so snovi, zgrajena iz ogljikovih atomov in imajo izjemne lastnosti, predvsem, ko sestavljajo kompozit. Njihova izdelava je zahtevna, toda končni produkt je kakovosten in zaradi tega dosega tudi visoke cene na trgu. Ogljikova vlakna so kar petkrat močnejša od železa, imajo visoko trdnost in so korozijsko odporna. So odlično električno prevodna, imajo visoko natezno trdnost in nizek koeficient toplotnega raztezka. Niso škodljiva za človeka in kar je skoraj najboljša lastnost, so nevnetljiva. Čeprav so ogljikova vlakna nevnetljiva, je vnetljivost še vedno velik problem, ko ogljikova vlakna združujemo v polimerne kompozite. Poznamo tri najpogostejše polimerne osnove, ki se uporabljajo v kompozitih. To so epoksi, vinilester in poliesterska smola (poliesterska smola je le redko uporabljena z ogljikovimi vlakni). Vsak kompozit ima polimerno osnovo, ki je vnetljiva, zato se za visoko stopnjo nevnetljivosti, kompozitom dodajajo snovi, ki vnetljivost zavirajo. Pravimo jim zaviralci gorenja. Zaviralce gorenja lahko nanašamo v kompozit na različne načine. Lahko jih vmešamo v polimer med procesom izdelave, lahko jih kemijsko vgradimo v glavno polimerno verigo. Uporabimo lahko tudi zaviralce gorenja, ki se nanašajo kot zaščitna plast ali pa sami od sebe tvorijo zaščitno last, ko pridejo v stik z dovolj visokimi temperaturami. Zaviralce gorenja v splošnem delimo na fosforjeve, dušikove, halogenske, intumescenčne ter anorganske. Halogenski zaviralci gorenja temeljijo na dveh elementih, kloru in bromu, anorganski pa na aluminiju in magneziju. Anorganski zaviralci gorenja večinoma dodajamo le kot katalizatorje, da pospešijo delovanje drugih zaviralcev gorenja, ki so dodani kompozitu. Intumescenčni zaviralci gorenja ob povišanih temperaturah tvorijo zaščitno plast, ki varuje kompozit pred vžigom in razpadom. Za polimerne kompozite z ogljikovimi vlakni se večinoma uporabljajo halogenski in fosforjevi zaviralci gorenja. Prav fosforjevi zaviralci gorenja so začeli nadomeščati halogenske predvsem zato, ker so halogenski zaviralci gorenja škodljivi za človeka in okolje. Učinkovitost zaviralcev gorenja lahko določamo z različnimi tehnikami. Navadno merimo mejno vrednost kisika, to je koncentracija kisika, pri kateri snov še gori, lahko izvedemo skupino testov UL-94 ali pa s kalorimetrijo izmerimo sproščanje toplote in z rentgensko fotoelektronsko spektroskopijo spremljamo sestavo kompozita. Z dodajanjem zaviralcev gorenja kompozitnim materialom, se soočamo tudi z nevšečnostmi. Če pride do vžiga materiala in zaviralec ni učinkovit, lahko pride do učinka svečnega stenja, kjer gori polimer na ogljikovih vlaknih, vse dokler gorenje ni umetno prekinjeno oz. zmanjka goriva. Problem nastane tudi v polarnosti zaviralcev, kajti bolj polaren zaviralec gorenja kot polimerna osnova oslabi strukturo kompozita in privede do slabših mehanskih lastnosti. Danes se v kompozitih z ogljikovimi vlakni uporablja epoksi smola. Ker so materiali, zgrajeni iz epoksi smole lahki, lahko nadomestijo druge, prej težje materiale, kar je uporabno predvsem v letalski in avtomobilski industriji. Sprva so se takšnim kompozitom dodajali halogeni zaviralci gorenja, danes pa se zaradi nevarnosti vedno bolj uporabljajo fosforjevi. Potrebno je dobro poznati tako lastnosti zaviralcev gorenja kot tudi kompozita, da lahko dosežemo dobro odpornost proti vnetljivosti in tako še izboljšamo lastnosti polimernim kompozitom z ogljikovimi vlakni.

Ključne besede

kemija polimerov;polimeri;polimerni kompoziti;ogljikova vlakna;epoksi smole;vinilestrske smole;poliestrske smole;vnetljivost;zaviralci gorenja;diplomska dela;

Podatki

Jezik:	Slovenski jezik
Leto izida:	2019
Tipologija:	2.11 - Diplomsko delo
Organizacija:	UL FKKT - Fakulteta za kemijo in kemijsko tehnologijo
Založnik:	[L. Skubic]
UDK:	678:614.84(043.2)
COBISS:	1538277571
Št. ogledov:	442
Št. prenosov:	93
Ocena:	0 (0 glasov)
Metapodatki:

Ostali podatki

Sekundarni jezik:	Angleški jezik
Sekundarni naslov:	Flammability of polymer composites reinforced with carbon fiber
Sekundarni povzetek:	Carbon fibres mainly consist of carbon atoms and they have some outstanding properties, especially when it is integrated in a composite. Although the production of carbon fibres is complex, the final product has great quality, which is why carbon fiber materials are expensive in the market. Carbon fibres are five times stronger than iron as well as rigid and corrosion resistant. Electric conductivity of carbon fibres and their tensile strength are high and thermal expansion coefficient is low. They are not poisonous for people in addition to not being flammable, which is one of their best features. Flammability, however is still a very big problem, when carbon fibres are put into polymer composites. There are three main polymer matrices, which can be used in polymer composites: epoxy resin, vinylester resin and polyester resin , which is rarely used with carbon fibres. Since almost every polymer has a polymer matrix which is flammable, special materials are added to the composites in order to make them non-flammable. They are called flame retardants and they can be integrated into composites in different ways. They can either be added to polymer matrix during the production process or they can be integrated in the main polymer chain. Flame retardants, which are added as protective coating or which form protective coatings during the exposure to high temperatures can also be used. In general, flame retardants can be divided to phosphorous, nitrogen, halogen, intumescent and inorganic flame retardants. Halogen flame retardants mainly contain one of two elements (chlorine or bromine) and inorganic flame retardants are generally made of aluminium or magnesium. Inorganic flame retardants are mostly used as catalysts, so they speed up the effect of other flame retardants added to the composite. Intumescent flame retardants create a protective layer at high temperatures, which protects composite from ignition and degradation. Mainly halogen and phosphorus flame retardants are used for polymer composites with carbon fibres. Since halogen retardants appear to be harmful to people and to the environment, phospohorous flame retardants started to be used as a substitute. Effectiveness of flame retardants can be determined by using various techniques. Most commonly the limiting oxygen index, and shows the percentage, where material still burns. In addition group of UL-94 tests can be performed or determine heat release with calorimetry or we can watch a chemical composition of product with x-ray photoelectron spectroscopy. Because of the addition of flame retardants to composite materials, several problems emerge. If the ignition of material happens and the flame retardants are not effective, a candlewick effect could happen. This means that the polymer is burning on carbon fibres until fire is turned down artificially or the fuel runs out. Another problem occurs in the polarity of flame retardants; if flame retardant is more polar than polymer matrix, structure of composite becomes weak, which leads to bad mechanical properties. Nowadays, epoxy resin is mostly used in polymer composites with carbon fibres. Materials from such substances can replace other, heavier materials, which is very useful in aviation and automobile industry. Firstly, halogen flame retardants were added to such composites, and because halogen flame retardants are toxic, more and more phosphorus flame retardants are used. Properties of flame retardants and composites have to be well researched, so that good flame retardancy can be reached and that is how polymer composites with carbon fibres properties are even improved.
Sekundarne ključne besede:	flammability;carbon fibres;polymer composites;flame retardant;
Vrsta dela (COBISS):	Diplomsko delo/naloga
Študijski program:	1000372
Komentar na gradivo:	Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, UNI Kemijsko inženirstvo
Strani:	30 str.
ID:	12365823