Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites

Nadka Dintcheva, Sahar Al-Malaika, Francesco P. la Mantia

Research output: Contribution to journalArticle

Abstract

Polyethylene (a 1:1 blend of m-LLDPE and z-LLDPE) double layer silicate clay nanocomposites were prepared by melt extrusion using a twin screw extruder. Maleic anhydride grafted polyethylene (PEgMA) was used as a compatibiliser to enhance the dispersion of two organically modified monmorilonite clays (OMMT): Closite 15A (CL15) and nanofill SE 3000 (NF), and natural montmorillonite (NaMMT). The clay dispersion and morphology obtained in the extruded nanocomposite samples were fully characterised both after processing and during photo-oxidation by a number of complementary analytical techniques. The effects of the compatibiliser, the organoclay modifier (quartenary alkyl ammonium surfactant) and the clays on the behaviour of the nanocomposites during processing and under accelerated weathering conditions were investigated. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), rheometry and attenuated reflectance spectroscopy (ATR-FTIR) showed that the nanocomposite structure obtained is dependent on the type of clay used, the presence or absence of a compatibiliser and the environment the samples are exposed to. The results revealed that during processing PE/clay nanocomposites are formed in the presence of the compatibiliser PEgMA giving a hybrid exfoliated and intercalated structures, while microcomposites were obtained in the absence of PEgMA; the unmodified NaMMT-containing samples showed encapsulated clay structures with limited extent of dispersion in the polymer matrix. The effect of processing on the thermal stability of the OMMT-containing polymer samples was determined by measuring the additional amount of vinyl-type unsaturation formed due to a Hoffman elimination reaction that takes place in the alkyl ammonium surfactant of the modified clay at elevated temperatures. The results indicate that OMMT is responsible for the higher levels of unsaturation found in OMMT-PE samples when compared to both the polymer control and the NaMMT-PE samples and confirms the instability of the alkyl ammonium surfactant during melt processing and its deleterious effects on the durability aspects of nanocomposite products. The photostability of the PE/clay nanocomposites under accelerated weathering conditions was monitored by following changes in their infrared signatures and mechanical properties. The rate of photo-oxidation of the compatibilised PE/PEgMA/OMMT nanocomposites was much higher than that of the PE/OMMT (in absence of PEgMA) counterparts, the polymer controls and the PE–NaMMT sample. Several factors have been observed that can explain the difference in the photo-oxidative stability of the PE/clay nanocomposites including the adverse role played by the thermal decomposition products of the alkyl ammonium surfactant, the photo-instability of PEgMA, unfavourable interactions between PEgMA and products formed in the polymer as a consequence of the degradation of the surfactant on the clay, as well as a contribution from a much higher extent of exfoliated structures, determined by TEM, formed with increasing UV-exposure times.
Original languageEnglish
Pages (from-to)1571-1588
Number of pages18
JournalPolymer Degradation and Stability
Volume94
Issue number9
DOIs
Publication statusPublished - Sep 2009

Fingerprint

Photooxidation
photooxidation
Polyethylene
clays
Extrusion
Polyethylenes
polyethylenes
Nanocomposites
nanocomposites
Clay
Surface-Active Agents
Surface active agents
Bentonite
Ammonium Compounds
surfactants
Polymers
montmorillonite
Clay minerals
polymers
Processing

Keywords

  • clay–PE nanocomposites
  • processing
  • photo-oxidation
  • polyethylene-graft-maleic anhydride

Cite this

Dintcheva, Nadka ; Al-Malaika, Sahar ; la Mantia, Francesco P. / Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites. In: Polymer Degradation and Stability. 2009 ; Vol. 94, No. 9. pp. 1571-1588.
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Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites. / Dintcheva, Nadka; Al-Malaika, Sahar; la Mantia, Francesco P.

In: Polymer Degradation and Stability, Vol. 94, No. 9, 09.2009, p. 1571-1588.

Research output: Contribution to journalArticle

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AU - Dintcheva, Nadka

AU - Al-Malaika, Sahar

AU - la Mantia, Francesco P.

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