A. Crespy

Mechanical behaviour of polypropylene composites containing fine mineral filler: Effect of filler surface treatment

Abstract The inclusion of mineral fillers in thermoplastics improves some mechanical properties but reduces others, such as impact strength. However, the use of ultrafine fillers limits this degradation. The influence of two surface treatments on the mechanical properties of polypropylene/ultrafine-kaolin composites was studied. In the first treatment, stearic acid was used on dry powder, and the second was a cationic treatment with quaternary ammonium in suspension. An improvement in the impact strength was found when the second agent was used. This can be explained from both macroscopic and microscopic points of view. We observe a better particle dispersion in the matrix and thermal analysis indicates that the crystalline structure of these materials is finer. In addition, tensile tests carried out on matrix/agent blends show that a soft interface around each particle could act as a shock absorber during an impact test.

Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/ talc) has been investigated. The release of water from Mg(OH) 2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH) 2 , appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH) 2 loading in ternary compositions.

Flame retardant and mechanical properties of a copolymer PP/PE containing brominated compounds/antimony trioxide blends and magnesium hydroxide or talc

The incorporation of two brominated compounds/antimony trioxide blends into a PP–PE copolymer were studied. Both brominated trimethylphenyl indane (FR 1808) and poly(pentabromobenzyl acrylate) (FR 1025) confer good flame retardancy at 40% loading. A comparison was made with the incorporation of magnesium hydroxide at higher loadings (up to 64%) in the same copolymer. The mineral filler improves both fire resistance and stiffness of the copolymer, nevertheless the high loading causes a dramatic decrease in impact resistance. Moreover, the necessary surface treatment of the filler significantly lowers the maximal tensile strength. In order to maximize both fire resistance and mechanical properties, we combined each brominated flame-retardant system (20% in weight) with magnesium hydroxide or talc (20% in weight). Talc is used as reference. These composites show interesting fire-retardant properties in comparison with the copolymers containing only 40% of the brominated flame-retardant systems. In addition, the mechanical properties are on the whole improved.

Red phosphorus/aluminium oxide compositions as flame retardants in recycled poly(ethylene terephthalate)

Abstract The mechanical properties and fire resistance of a recycled poly(ethylene terephthalate) were improved by using a specific treatment of the waste material and the incorporation of encapsulated red phosphorus in combination with co-additives. The use of red phosphorus has to be limited due to a negative influence on impact resistance and rate of heat release. Among several metal oxides, Al 2 O 3 acts as a good co-synergist at a total loading of 5 wt.% due to its reactivity, high specific surface area and aluminium phosphate formation. The complementary use of glass fibres can also generate intumescence by improving the mechanical stability of the char layer.

Fire resistance and mechanical properties of a huntite/hydromagnesite/antimony trioxide/decabromodiphenyl oxide filled PP-PE copolymer

A natural mineral filler containing mainly huntite and hydromagnesite together with a blend of antimony trioxide (Sb2O3) and decabromodiphenyl oxide (DBDPO) was used to reduce the flammability of an ethylene-propylene copolymer. At the same time it was desirable to improve the stiffness of the copolymer without damaging its impact resistance even at high filler content. All the components and the resulting composites were studied by differential thermal (DTA) and thermogravimetric analysis (TGA). Specific flammability tests and mechanical tests were also carried out on the composites. The influence of the mineral filler and/or the Sb2O3/DBDPO blend on copolymer properties was investigated. The best results were obtained by combining both of the main components to give 25% mineral filler and 20% Sb2O3/DBDPO blend.

Influence of a fine talc on the properties of composites with high density polyethylene and polyethylene/polystyrene blends

Fine talc filled high density polyethylene (HDPE) and HDPE/polystyrene (PS) blends were extruded, injection moulded and characterized. Some of the mechanical properties of the talc filled HDPE and talc filled 75/25 HDPE/PS blend were deduced from stress–strain measurements. A comparison between the effect of the talc on the properties of the filled HDPE and filled 75/25 HDPE/PS blend showed that the mineral filler had the same effect on both systems provided that its array in the organic matrix is almost the same in both cases. In fact, the rheological results proved that the dispersion of talc in the HDPE matrix was not really affected by the presence of PS. The study particularly focused on the effect of talc on the ultimate tensile strength of the filled HDPE and that of the filled blend. It has been noted that the brittle nature of PS neutralizes, to a certain extent, the degrading effect of talc on this property. Furthermore, both PS and talc have a complementary effect on the stiffness and the resilience of HDPE/PS/talc blend composites.

Granulometric Characterization of Short Fiberglass in Reinforced Polypropylene. Relation to Processing Conditions and Mechanical Properties

Abstract In most cases, for reinforced thermoplastics, a knowledge of average filler length is not enough information. The entire granulometric filler distribution needs to be known, if structure is to be correlated with properties. We have developed a technique of granulometric determination based on image analysis to analyse rapidly the evolution of the granulometry of short fiberglass. Once images in grey levels from polarized light microscopy have been acquired, each selected fiber on the frame is individualized and labelled before measurement and data treatment. For the fiber, the size factor chosen is the length, or the maximum Feret diameter. With this tool, we have been able to study more precisely the evolution of the fiber length distribution during processing with a polypropylene matrix. Finally, we elucidate the dependence of mechanical properties such as impact and tensile strengths on glass filler size.

Study of the degradation of fire-retarded PP/PE copolymers using DTA/TGA coupled with FTIR

Abstract A PP/PE copolymer was successively flame retarded using Mg(OH) 2 , then using brominated trimethylphenyl indane associated with Sb 2 O 3 (Br/Sb), and finally using blends of equal weights of this last combination with Mg(OH) 2 or talc-containing non-hydrated fillers. Decompositions of pure and additive-containing copolymer were studied by DTA/TGA coupled with FTIR. A good correlation exists between the maxima of Gram–Schmidt curves and the derivatives of TGA curves. The coupling of techniques shows that the incorporation of the Br/Sb flame retardant limits strong exothermic phenomena due to sample ignition. In the case of Mg(OH) 2 associated with Br/Sb, the decomposition of the hydrated mineral occurs at a lower temperature than the reaction between brominated trimethylphenyl indane and Sb 2 O 3 . This delays the action of Br/Sb flame retardant towards higher temperatures, improving the thermal stability of the polymer. A good agreement is also found between DTA/TGA-FTIR conclusions and fire resistance tests carried out on standardized samples. When magnesium hydroxide is replaced by the fillers, the interest in using a pure talc, which appeared in fire resistance tests, is not strongly confirmed by DTA/TGA-FTIR. This discrepancy may be ascribed to the reduced influence of mass diffusion phenomena due to the small weight of the sample used in thermal analysis experiments.

Determination of the microtexture of reinforced thermoplastics by image analysis

Abstract The mechanical properties of reinforced thermoplastics depend on such characteristics of the filler as granulometry, orientation and dispersion. These different microtextural parameters were determined by using a single tool: image analysis, which was coupled with optical and electron microscopies. The different materials tested were based on short-glass-fibre-reinforced polypropylene obtained by extrusion and injection steps. For the different samples analysed, the processing conditions and the filler concentration were constant, and variability was due to the different average lengths of the filler incorporated in the matrix. The different filler parameters were determined with particular emphasis on the techniques of dispersion characterisation. The techniques developed in this study were based on image analysis. They enabled us to estimate filler-size distribution and development of the three-dimensional orientation inside the material and between different samples. The development of the filler dispersion was also made apparent. In addition, the relationships obtained between the different microtextural parameters were investigated. The general conclusion is that image analysis is very suitable for characterisation of this kind of material.

The Combined Action of Huntite and Hydromagnesite for Reducing Flammability of an Ethylene-Propylene Copolymer

Abstract The flammability of a filled ethylene-propylene copolymer is discussed. A mineral filler with 40% of hydromagnesite and 60% of huntite by weight is used as a flame retardant additive. Some burning characteristics and mechanical properties have been studied in relation to the amount of incorporation. Flammability was measured by the oxygen index method, the dripping test and the rate of spread of flame test. Thermal degradation was investigated by differential scanning calorimetry and thermogravimetry in combination with differential thermal analysis.