P OLYMER N ANOCOMPOSITES
IN T HIN F ILM A PPLICATIONS
Linda Fogelström
AKADEMISK AVHANDLING
som med tillstånd av Kungliga Tekniska högskolan i Stockholm framlägges till offentlig granskning för avläggande av teknisk doktorsexamen.
Fredagen den 7 maj 2010, kl 10.00 Sal D1, Lindstedtsvägen 17, KTH, Stockholm
Fakultetsopponent:
Prof. José M Kenny
Instituto de Ciencia y Tecnología de Polímeros (ICTP‐CSIC), Madrid, Spanien
Stockholm 2010
Linda Fogelström: Polymer Nanocomposites in Thin Film Applications.
Doctoral thesis in Polymer Technology from the School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden, 2010.
TRITA‐CHE‐Report 2010:12, ISSN 1654‐1081, ISBN 978‐91‐7415‐615‐7
A BSTRACT
The introduction of a nanoscopic reinforcing phase to a polymer matrix offers great possibilities of obtaining improved properties, enabling applications outside the boundaries of traditional composites.
The majority of the work in this thesis has been devoted to polymer/clay nanocomposites in coating applications, using the hydroxyl‐functional hyperbranched polyester Boltorn® as matrix and montmorillonite clay as nanofiller.
Nanocomposites with a high degree of exfoliation were readily prepared using the straightforward solution‐intercalation method with water as solvent. Hard and scratch‐resistant coatings with preserved flexibility and transparency were obtained, and acrylate functionalization of Boltorn® rendered a UV‐curable system with similar property improvements. In order to elucidate the effect of the dendritic architecture on the exfoliation process, a comparative study on the hyperbranched polyester Boltorn® and a linear analogue of this polymer was performed. X‐ray diffraction and transmission electron microscopy confirmed the superior efficiency of the hyperbranched polymer in the preparation of this type of nanocomposites.
Additionally, an objective of this thesis was to investigate how cellulose nanofibers can be utilized in high performance polymer nanocomposites. A reactive cellulose “nanopaper” template was combined with a hydrophilic hyperbranched thermoset matrix, resulting in a unique nanocomposite with significantly enhanced properties. Moreover, in order to fully utilize the great potential of cellulose nanofibers as reinforcement in hydrophobic polymer matrices, the hydrophilic surface of cellulose needs to be modified in order to improve the compatibility. For this, a grafting‐from approach was explored, using ring‐opening polymerization of ε‐
caprolactone (CL) from microfibrillated cellulose (MFC), resulting in PCL‐modified MFC. It was found that the hydrophobicity of the cellulose surfaces increased with longer graft lengths, and that polymer grafting rendered a smoother surface morphology. Subsequently, PCL‐grafted MFC film/PCL film bilayer laminates were prepared in order to investigate the interfacial adhesion. Peel tests demonstrated a gradual increase in the interfacial adhesion with increasing graft lengths.
Keywords: Nanocomposites, hyperbranched polymers, montmorillonite, clay nanoparticles, exfoliated, coatings, crosslinking, TEM, XRD, mechanical properties, thermal properties, cellulose nanofibers, Atom Transfer Radical Polymerization, Ring‐Opening Polymerization, poly(ε‐caprolactone), surface modification, grafting, interfacial adhesion
