Thermal properties and stability of PE/MWCNT nanocomposites

Polimeri sve više zamjenjuju obične materijale te je istraživanje njihovih svojstava važan korak prema stvaranju materijala sa poboljšanim svojstvima. U ovom radu cilj je bio istražiti utjecaj višestijenih ugljikovih nanocjevčica (MWCNT), masenih udjela od 0,5 do 4 mas %, na toplinska svojstva i stabilnost polietilena niske gustoće PE-LD te polietilena visoke gustoće PE-HD. Toplinska svojstva u neizotermnim i izotermnom uvjetima ispitivana su tehnikom diferencijalne pretražne kalorimetrije (DSC), a toplinska stabilnost termogravimetrijskom analiztom (TGA). Uzorci nanokompozita PE-LD/MWCNT i PE-HD/MWCNT pripravljeni su u dvopužnom ekstruderu te zatim prešanjem u hidrauličkoj preši. Uzorci su sadržavali od 0-4 mas % nanopunila MWCNT. DSC analiza u neizotermnim uvjetima je pokazala da PE-HD brže kristalizira i ima uređeniju strukturu u odnosu na PE-LD. Do određenog udjela, dodatak MWCNT ubrzava kristalizaciju PE-HD matrice te potiče kristalizaciju PE-HD matrice što je najizraženije u sustavu s 1 % mas. udjela nakon čega se učinak smanjuje. Također, dodatak MWCNT matrici PE-LD ubrzava kristalizaciju što je najizraženije u sustavu s 3 % mas udjela nakon čega se učinak smanjuje. Male količine punila MWCNT do 0,5 mas % neznatno potiču kristalizaciju PE-LD matrice dok daljnji dodatak ometa kristalizaciju. Entalpije kristalizacije i entalpije taljenja za nanokompozitni sustav PE-LD/MWCNT su različite dok su za nanokompozitni sustav PE-HD/MWCNT sličnih vrijednosti što ukazuje da PE-HD ima savršenije kristalne strukture te da su procesu zagrijavanja ne dolazi do rekristalizacije. Također, DSC analiza je pokazala da dodatak punila ubrzava izotermnu kristalizaciju PE-LD i PE-HD matrica. Rezultati termogravimetrijske analize (TGA) pokazali su da bolju toplinsku stabilnosti ima matrica PE-HD u odnosu na PE-LD te da dodatak MWCNT poboljšava toplinsku stabilnost obje polietilenske matrice pri čemu je učinak znatno izraženiji za PE-HD.Polymers are common substitutes for the usual materials so their research is very important step towards creation of materials with improved performances. The objective of this study was to determine influence of multiwall carbon nanotubes (MWCNT), in amount from 0,5 to 4 % wt, on thermal properties and stability of low-density polyethylene (PE-LD) and high-density polyethylene (PE-HD). Thermal properties under isothermal and non-isothermal conditions were investigated by differential scanning calorimetry (DSC) and thermal stability was determined by thermogravimetric analysis. Nanocomposite samples PE-LD/MWCNT and PE-HD/MWCNT were prepared in twin screw extruder and then pressed on hydraulic press. Samples containing from 0-4 % wt of MWCNTs were prepared. DSC analysis under non-isothermal conditions showed that crystallization of PE-HD is faster and more arranged crystals are formed than in PE-LD. Till certain amount, addition of multiwall carbon nanotubes accelerates crystallization and raises crystallization of PE-HD matrix which is the most prominent in the system with 1 % wt MWCNT after which this effect decreases. Also, addition of MWCNT to the matrix PE-LD accelerates crystallization which is the most prominent in the system with 3 % wt MWCNT after which the effect decreases. Small amounts of fillers till 0,5 % wt MWCNT slightly raises crystallization while further addition disrupts crystallization. Enthalpy of crystallization and melting enthalpy of the nanocomposite system PE-LD/MWCNT are different while for the nanocomposite system PE-HD/MWCNT have similar values which points out that the PE-HD has the perfect crystal structure and that in process of heating there is no recrystallization. Also, DSC analysis showed that addition of the fillers accelerates isothermal crystallization both PE-LD and PE-HD matrix. Results of the thermogravimetric analysis showed that matrix PE-HD is more thermally stable than the PE-LD matrix and that addition of the MWCNT improves thermal stability of both polyethylene matrices wherein that effect is the more prominent for PE-HD matrix