Study of the Addition of a Thermoplastic Vulcanizate to a HDPE Composite Highly Filled with Magnesium Hydroxide and Its Effect on the Tensile and Flame Retardant Properties

A work was carried out in order to obtain a TPV based on HDPE and EPDM, studying the effect of three different peroxides. The effect of one mono- and two bifunctional peroxides was studied. In general, at equal wt% of peroxide, the bifunctional peroxides produced greater gel content, higher tensile stress, and higher elongation at break. Thereafter, the work was focused on studying the effect of this TPV, as well as a commercial TPO, on the tensile and flame retardant properties of composites based on blends of HDPE and a thermoplastic elastomer (either TPV or TPO), plus 130 phr of magnesium hydroxide (MH). The composites without the rubbery phase, but with 130 phr of MH, were highly brittle and fragile. The composites with the rubbery phase, on the other hand, (either TPO or TPV), were tougher and presented relatively much higher tensile properties. With regard to flame retardancy, the formulations containing the TPV showed better flame retardancy and passed as V-1 in the UL-94V. With respect to the cone calorimeter, those with TPO or TPV all generated a total of 80 MJ of heat energy. The compositions with TPV, however, generated this amount of heat over a larger period of time, i.e., showing less heat generated per second. In addition, the compositions with TPV presented a markedly lower pHRR, by an average of 15%. Thermogravimetric analysis (TGA) showed that the MH in the samples with a 40 wt% rubbery phase starts decomposing at 315°C. However, as the temperature increases, the MH in the TPV composite apparently decomposes at a slower rate than that in the TPO composite.

Silane Functionalized Ethylene/Diene Copolymer Modifiers in Composites of Heterophasic Polypropylene and Microsilica

Ethylene/1,7-octadiene copolymer was polymerised with metallocene catalyst and hydrosilylated to form silane functionalised polyethylenes (PE-co-SiX, X=Cl, OEt, Ph). The functionalised species were tested as modifiers in composites of rubber toughened polypropylene (heterophasic PP, hPP) and microsilica filler (μSi). A metallocene-based functionalised PE (PE-co-SiF) produced earlier in our laboratory and three commercial grades of functionalised polyolefins (one PE- and two PP-based) were used as reference modifiers. Major differences were seen in the toughness of the composites both above and below the glass transition temperature (Tg) of PP. In addition to increasing the stiffness, the microsilica filler enhanced the toughness of the heterophasic polypropylene by over 200% at ambient temperature. Below the Tg of PP (at −20 °C), the influence of μSi was the opposite and the impact strength of the hPP/μSi composite was below that of unfilled hPP. With the addition of just 2 wt% of functionalised polyethylene, the poor cold toughness of hPP/μSi composite was improved by nearly 100%. With the same addition, the toughness of the composites at ambient temperature was improved by 50 to 100% compared with the unfilled hPP. This behaviour was explained by significant changes in the fracture mechanism. Addition of functionalised PE increased the concentration of microsilica in the rubbery phase, allowing the crack to enter that phase. The rubbery phase was also able to absorb a large amount of impact energy below the glass transition temperature of PP.

Toughening of Polypropylene Highly Filled with Aluminum Hydroxide

The flame retardant and mechanical properties of polypropylene (PP), highly filled with aluminum hydroxide (Al(OH)3) and toughened with ethylene propylene diene monomer (EPDM) and zinc neutralized sulfated EPDM ionomer (Zn-S-EPDM), were studied along with their morphology. The PP matrix when highly filled with Al(OH)3 particles can achieve an adequate level of flame retardancy, but there is a decrease in the mechanical properties because of inadequate adhesion between the Al(OH)3 particles and the PP matrix and the strong tendency of the filler to agglomerate. The rubber incorporated in the PP/Al(OH)3 composites has two roles: as compatibilizer and toughening agent. Although ordinary EPDM significantly improves the Izod impact strength of the composites, the tensile properties are much worse because of the weak interfacial adhesion between the modifier and the matrix. Using Zn-S-EPDM instead EPDM, the tensile properties are much improved with only a slight decrease in toughness, because of improvements in the interfacial adhesion between modifier and matrix. SEM micrographs show that the rubber phase is dispersed in the continuous PP matrix and that most Al(OH)3 particles are uniformly distributed in the rubbery phase. Larger, obviously rubbery, domains can be seen in the PP/EPDM/Al(OH)3 ternary composites. Much finer rubbery domains were found in the PP/Zn-S-EPDM/Al(OH)3 composites.

The Second Expansion Cycle in Ultramicrocellular Foams

Ultramicrocellular PMMA foams made from the low temperature rubbery phase, obtained by saturating the polymer with CO2 at 0°C and 34 atm, was subjected to a second expansion cycle by heating it rapidly to temperatures in the range 30 to 120°C. The blowing agent for the secondary expansion was either the residual CO2 in the foam at about 19 wt% level or fresh CO2 re-equilibrated at 0°C and 34 atm to a loading level of about 29 wt%. In the former case, the second expansion cycle led to lower foam densities whereas in the latter case it led to stretching and re-orientation of the cell walls with no significant gain in further foam density reduction or cell density increase.

Development of Some Promising Approaches for The Toughening of High-Temperature Polymers

High-temperature poly(arylene ether) and hydroxypolybenzoxazole polymers were toughened using dispersed rubbery phases. This rubbery phase was a hybrid material which was in-situ generated within the polymer matrix using mixtures of partially-hydrolyzable trialkoxy and dialkoxy organosilanes with a fully hydrolyzable tetraalkoxysilane. The resulting materials were characterized with regard to their structures, mechanical properties (modulus, ultimate strength, maximum extensibility, and toughness), thermal properties, optical properties, and tendencies to absorb water. Some of the results are presented here.