Plasticized PVC Nanocomposites - The Effect of Montmorillonite Treatment and Processing Conditions on Material Properties
Polyvinyl chloride (PVC) is one of the world’s most widely produced polymers. Its products are used in a wide range of areas such as building and construction, packaging, automotive, electrical/electronic and healthcare. PVC can easily be tailored to adapt material properties to specific applications. This is largely achieved by adding certain components to the PVC material formulation. Some of these additives are essential for PVC processing, such as heat stabilizers. Others greatly alter the material properties, like for example plasticizers that makes the material soft and flexible.
Nano-sized fillers have the advantage to remarkably improve material properties even at very low additions. Among nanoclays layered silicates have been widely studied and are known to improve mechanical properties and to add barrier properties to a material. Montmorillonite (MMT) is the most commonly used nanoclay for processing with polymers.
In this thesis the aim was to organically modify MMT to be suitable for incorporation in plasticized PVC. For this purpose novel methods for organomodification of MMT was developed in order to avoid the use of commercially available organoclays (OMMT) which are known to catalyse dehydrochlorination of PVC.
A solid-liquid state method to produce OMMTs was developed and plasticized PVC composite materials were processed. Composite materials were characterized with X-ray diffraction (XRD), mechanical testing, Scanning Electron Microscopy (SEM), gas permeability, cone calorimetry, Vicat softening temperature (VST), thermogravimetric analysis (TGA) and determination of hardness.
It was found that the addition of 10 phr sodium MMT to a tributyl citrate (TBC)-plasticized PVC significantly improved the material properties. Increased E-modulus by up to 182 %, nearly halved oxygen permeability and a significantly reduced total smoke released (TSR) by 37 % in fire testing. The whole manufacturing process of composite materials was developed to be free from solvents, prepared by dry-blending in a high-speed mixer followed by two-roll milling.
scanning electron microscopy
VDL-salen, Hörsalsvägen 7 (Chalmers Tvärgata 4C), Göteborg.
Opponent: Prof. Ulf Gedde, Fiber och Polymerteknologi, Kemivetenskap, KTH, Sverige