Gy. Marosi

Effect of fillers on the fire retardancy of intumescent polypropylene compounds

Abstract The effects of fillers (talc and calcium carbonate) were investigated on polypropylene /ammonium polyphosphate/polyamide-6 (PP/APP/PA-6) intumescent system by using mechanical testing, LOI method, cone calorimetry and thermoanalytical techniques. Calcium carbonate and talc affect the fire protective properties of PP/APP/PA-6 system in different ways. It is shown that talc induces an increase in the Youngs modulus and a decrease in the elongation at break. Calcium carbonate leads to a decrease in the elongation at break, but there is no improvement in the Youngs modulus. Talc increases fire protective performance due to forming a ceramic like protective shield at the surface, whereas calcium carbonate decreases it because of a reaction with APP. Effects of talc and calcium carbonate were furthermore investigated on PP/APP/PA-6 system by measuring Rate of Heat Release (RHR), Total Heat Emitted (THE), CO/CO 2 evolution and residual mass. Results are interpreted by means of decomposition, chemical reaction between components and formation of a protective shield at the surface at ignition.

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.

Using polyamide 6 as charring agent in intumescent polypropylene formulations: II. Thermal degradation

The fire performance of intumescent PP/APP/PA6/EVA19 blends were previously put forward in part I of this article. In the present part, the thermal and thermo-oxidative degradations of the formulations are modelled. The comparison between the kinetic data determined in this study and data from previous studies suggests that PP degrades before the reaction between APP and PA6. However it may be supposed that in the conditions of a fire (i.e. at high heating rate) both reactions occur simultaneously. Thus the development of an efficient protective structure is possible which could explain the fire properties of interest observed in the conditions of the cone calorimeter.

Using polyamide-6 as charring agent in intumescent polypropylene formulationsI. Effect of the compatibilising agent on the fire retardancy performance

Abstract Addition of the ammonium polyphosphate/polyamide-6 blend is known to enable fire properties of interest to be obtained in many polymers. However, the use of an interfacial agent is required to stabilise the formulation. This study investigates the improvement of the fire performance induced by incorporation of ethylene–butyl acrylate–maleic anhydride (EBuAMA) and ethylene vinyl acetate (EVA x , where x is the vinyl acetate weight level) as interfacial agents of the polypropylene/ammonium polyphosphate/polyamide-6 blend. It is shown that the improvement strongly depends upon both the nature and the amount of interfacial agent used.

Role of interfacial layers in the properties of particle-filled polyolefin systems

Abstract Modified interfacial layers were studied in polypropylene—calcium carbonate systems compounded in a single-step process with a surface-active agent and an elastomer simultaneously. Samples with etched and non-etched surfaces were investigated by dielectric spectroscopy and scanning electron microscopy. An increase in the thickness of the interfacial layer was brought about by the increasing elastomer content of the system. However, when the concentration of the latter exceeded a critical upper limit, a new disperse elastomer phase could be observed in the matrix. The value of the critical concentration depends upon the type of elastomer and it is a characteristic parameter for a given polymer—elastomer system. Deformations and failure in the composite system are determined by the interfacial layer. A thick elastomer interphase around the filler particles acts as a bumper layer and stops the crazes. The interactions between the components and the change in the mechanical properties induced by the presence of named additives were also investigated by mechanical spectroscopy.

Influence of modified rheology on the efficiency of intumescent flame retardant systems

Optimal concentration of boroxo siloxane elastomer synergist was determined by LOI and cone calorimetric measurements on ammonium polyphosphate and pentaerythritol containing intumescent flame retardant for polypropylene. The increased viscosity of the melt and plasticity of intumescent char due to boroxo siloxane elastomer could be proved by a thermal scanning rheometric investigation. It is presumed, the increased melt viscosity is created by the product of boroxo siloxane-pentaerythritol, formed during the compound preparation, while the improved char plasticity is the result of product formed at high temperature from boroxo siloxane and ammonium polyphosphate.

Elastomer interphase in particle filled polypropylene; structure, formation and mechanical characteristics

34 Introduction 34 Materials and Methods 35 Sample Preparation 37 Results and Discussion 37 References 59 Paper submitted for publication August 1991

Thermoanalytical study of nucleating effects in polypropylene composites: III. Intumescent flame retardant containing polypropylene

Engineering application of polypropylene requires the employment of flame retardants. Reactive compounding of ammonium-polyphosphate and synergist additives with polypropylene is an effective way for forming flame retardant polypropylene. Both the ammonium-polyphosphate and the additives used for improving its performance effect the crystallization and melting behavior of polypropylene. Encapsulation of flame retardant additives with appropriate elastomer, in order to improve their water resistancy, causes further changes in degree of crystallinity and consequently in the mechanical properties.