Andrea Márton

Ceramic precursor in flame retardant systems

Boroxo siloxanes were used as a ceramic precursor, combined with an intumescent flame retardant additive system, in polypropylene. Varying the composition and content of the precursor characteristic changes of melt viscosity were detected. Chemical interaction of the additives at the temperature of processing, confirmed using Fourier transformed infrared (FTIR) methods, are related with these rheological changes. Raman microscopic analyses were used to obtain better understanding of the chemical changes of the precursor during flame treatment. Interaction between boroxo siloxane and layered silicate (montmorillonite) nanoparticles was investigated using thermogravimetry.

Organosilicon surface layer on polyolefins to achieve improved flame retardancy through an oxygen barrier effect

A model system consisting of a polyethylene substrate surface treated by vinyltriethoxysilane and by organoboroxo-siloxane (OBSi), and an OBSi-containing intumescent flame-retarded compound (IFR-OBSi) based on polypropylene, ammonium polyphosphate and pentaerythritol were prepared and investigated. After a radio-frequency plasma treatment of the model system its oxygen permeability decreased by about one order of magnitude. According to XPS studies, enrichment of Si took place on the surface of the untreated IFR-OBSi, while after its ignition in a cone calorimeter surface enrichments of N and P were also detected. According to the evolution of the Si 2p peaks, creation of glass-like surface coatings took place on both the model system upon its RF plasma treatment and on IFR-OBSi upon its flame treatment. A small portion of OBSi remained unreacted in the surface layer of the flame-treated IFR-OBSi, which may ensure the plasticity necessary to prevent it from cracking and to ensure improved flame retardancy.

Fire retardancy effect of migration in polypropylene nanocomposites induced by modified interlayer

Montmorillonite nanoparticles were found to be inefficient in polypropylene because of the lack of a heat insulating char layer and the decomposition of the compatibilising surfactant layer on their surface. Combination with an ammonium polyphosphate-based intumescent system showed some synergism due to modified rheology. The effect of surface and interface modification was analysed using Raman microscopy and X-ray photoelectron spectroscopy. Forming a heat resistant coating layer of low surface energy around the nanoparticles promotes their migration to the surface and formation of a flexible barrier layer, and thus leads to better performance.

Role of pigments in the stability of polyethylene systems

The photodegradation processes of high-density polyethylene (HDPE) films containing either a phthalocyanine-based pigment, or a rutil (TiO 2 )-based pigment, as well as of the unpigmented films stabilised differently were investigated during photo-ageing, applying mechanical, gel content and XPS measurements. The phthalocyanine pigment-containing film showed degradation characteristics (abrupt decrease of elongation at break after short irradiation period, no gel formation, high concentration of oxygen-containg functional groups on the surface) similar to those of the films containing a low amount of stabiliser. The behaviour of the TiO 2 -containing film and that of the unpigmented films containing a higher amount of stabiliser were also similar (slow decrease of elongation at break, increase of gel content, lower amount of oxygen-containing functional groups on the surface). The concentration of oxygen-containing functional groups in samples pigmented with phthalocyanine increased remarkably with increasing processing temperature. The results suggest that the phthalocyanine pigment influences the photostability indirectly, through reduction of the thermal stability of polymer due to the adsorption of the thermal stabiliser by the phthalocyanine pigment. Coating the surface of phthalocyanine with reactive surfactant improved the photostability of the HDPE film.

New reactive additives for interface modification in multicomponent polyolefin systems

New reactive additives were synthesised and used as interface modifiers in different multicomponent polyolefine systems. The synthesis was carried out in computer-controlled reactor by means of Diels-Alder reaction and condensation. These additives are capable of combining the benefits of dispersing and coupling agents. A part of the synthesised reactive surfactants have also synergistic effect in flame retardant systems. Their surface-active character facilitates the reactive compounding. The undesirable transport processes of stabilisers and components of flame-retardants in polyolefine systems could be effectively controlled by interface modification.

Use of layered structures in recycling of polymers

Multilayer systems consisting of flame retarded and reinforced layers of recycled polymer were formed. The structure and the thickness of the interfacial layer between the phases were analysed by Differential Scanning Calorimetry and Raman microscopy. The sequence order of the layers was varied for achieving improvement in both the flame retardancy and mechanical performance of recycled polymers and for obtaining upcycled product this way. Investigation of injection moulded and compression moulded products demonstrated the advantage of reinforced core and flame retarded shell over the opposite structure. The multilayered structure was found an economic way for producing recycled polymer materials of improved fire resistance, flexural strength and modulus.

Reactive surfactants – new type of additive for multicomponent polymer systems

A new type of interfacial additive has been developed by the authors recently. The molecules of amphiphilic character are capable of forming chemical bonds at both the polar and the apolar sides. These reactive surfactants have been synthesised in a specially designed computer-controlled reactor system. The aim of the development was to combine the advantages of nonreactive surfactants and reactive coupling agents, making possible an in-line reactive interface modification during the compounding process of the polymer system. The characteristics and effects of the synthesised compounds were determined using methods of analytical and colloid chemistry, like Raman microscopy, surface tension, contact angle and rheological measurements.