Translation of a paper presented at the 20th Congress Science and Technology of Macromolecules. TERNI 11-15 September 2011

Mechanical characterization, rheological, thermal and morphological of  PA6 / ABS blends with different content of PA6 

C. Di Fiore^a, S. Taglialatela Scafati^a, P. Cerruti^b, M. Malinconico^b

^aCossa Polimeri srl, Via dei Brughiroli, 6 21050 Gorla Maggiore (VA)

^bICTP-CNR, Via Campi Flegrei,34 Comprensorio “Adriano Olivetti” 80078 Pozzuoli (NA)

Abstract. The growing economic interest towards the polymer alloys, especially for specific technological applications, such as in the automotive industry, leads the research and development of new polymer blends. In this work we have studied the characteristics of a series of blends of PA6 / ABS with different content of PA6. The samples of blends were analyzed from different point of view. Mechanically: tensile, flexural, impact, properties;  Rheologically:  viscosity / shear rate curves measured with capillary rheometer and MFI (melt flow rate); Thermally: temperature Vicat softening, DSC, DMA and TGA  analysis; and Morphologically: (SEM micrograph). The aim of this study was to correlate, if possible, the obtained values ​​of different properties to the content of PA6 in the blend.

1. INTRODUCTION 

In specific technological applications is now a well-established practice the use of polymer alloys in order to obtain new materials which combine the characteristics, in terms of chemical, physical or mechanical properties, of the individual blend components, through their mixing in the melt. PA/ABS is  polymer blend of great interest both academically, a lot of scientific literature1,2, has been produced, several patents were made on this blend3,  and there are big industrial interest (automotive sector).

The nylon represent an interesting class of polymers for technological applications which, although exhibiting suitable characteristics for many applications (good chemical resistance, good mechanical properties at high temperatures), however, have several unfavorable aspects such as high hygroscopicity and poor dimensional stability.In this study were prepared by a series of mixtures of PA6 / ABS with different compositions of PA6 containing a constant amount of butadiene. Indeed, given that the content of butadiene in ABS strongly influences the mechanical properties, eg. elastic modulus and Izod impact strength, as well as the thermal properties, eg. the Vicat softening temperature, to study the influence of the percentage of PA6 on the properties of the blend it was decided to maintain constant the  amount butadiene and evaluate how the growing presence of PA6 change the properties of the blend. 

The samples obtained were characterized in terms of mechanical (tensile properties, flexural, impact), rheological (MFI melt flow index, curves viscosity / shear rate), thermal (Vicat softening temperature, DSC analysis, DMA, and TGA ) and morphology (SEM micrograph). 


2. EXPERIMENTAL PART  

The blends, with growing PA6 content, as indicated in Tab. 1, were prepared by corotating twin screw extruder (model Labtech L / D = 40) operating at 300 rpm with temperatures of the cilinder between 240 and 260 ° C. Of each sample were printed specimens, dimensions conform to technical standards ASTM, by Sandretto injection molding machine. The rheological characterization was performed by CEAST capillary rheometer at a temperature of 240 ° C and nozzle L / D = 20/1 in the range of shear rates between 100 and 5000 s-1. The values ​​of Vicat softening temperature were measured, according to ASTM D1525, with instrument CEAST HDT Vicat 3, at 50 ° C / h and with weight  of 1 Kg and 5 Kg. The notched Izod impact strength values ​​were determined with pendulum CEAST RESIL 5.5. Both properties tensile and bending were obtained using a dynamometer INSTRON 4467 equipped with indicator strain. The morphological study was conducted by means of scanning electron microscopy (SEM FEI Quanta 100) observing the fracture surfaces of specimens broken in liquid nitrogen and metallized with a gold-palladium mixture. Finally, the thermal analysis DSC was performed using a Pyris 6 DSC Perkin Elmer with the following temperature program: 30 to 260 at 10 ° C / min, from 260 ° C to 30 ° C to 10 ° C / min, from 30 ° C to 260 ° C at 10 ° C / min.

Tab. 1: Composition of the samples.

CAMPIONE	COMPOSIZIONE	CAMPIONE	COMPOSIZIONE
PA 0	ABS 100%	PA40	PA6 40% ABS 60%
PA10	PA6 10% ABS 90%	PA50	PA6 50% ABS 50%
PA20	PA6 20% ABS 80%	PA60	PA6 60% ABS 40%
PA30	PA6 30% ABS 70%	PA65	PA6 65% ABS 35%

3 RESULTS AND DISCUSSION 

The Izod impact strength values ​​at 23 ° C, shown in Fig. 1, reveal that the Izod impact strength of only ABS is not appreciably influenced by the presence of PA6 for contents up to 10% (sample PA10), while the presence in a concentration higher PA6 in the blend (up to 30%) is manifested as a defect induced in the morphological structure, making the compound more fragile. The Izod impact strength values ​​show, however, between the PA30 and the PA40 an increase in impact strength from 204 J / but values ​​greater than 620 J / m. This shows that in this range of composition is achieved a significant degree of adhesion at the interface between the components, resulting in effective dissipation of the impact energy. A sensitive change of characteristics, in this composition range, is also found in the values ​​of softening temperature VICAT: from 125 ° C to 171 ° C of PA30 PA40 of (see Fig. 2). As reported is further confirmed by morphological analisys (Fig. 3) between these two compositions shows that a change in morphology, with one aspect of the ductile fracture for the sample PA40, characterized by the frequent variation of the direction of propagation of the fracture, differently from the sample PA30, for which the surface shows a brittle-type fracture, with fracture lines that propagate along the sample without interruption. Since the length of the path of a fracture is related to the ability of the sample to dissipate energy, frequent changes in direction lead to a lengthening of the path of the fracture, and thus to higher values ​​of resilience. It is evident that, for compositions in which PA6 is present at 40% or greater, it determines an inversion of phase, with the polyamide as a continuous phase and the dispersed phase as ABS. To maintain constant the content of butadiene, the copolymer, as the alloy is enriched in PA6, must contain a fraction butadiene higher, and consequently manifest a more elastomeric behavior. Furthermore, since the energy at the interface between phase and polyamide elastomeric phase decreases drastically when the polyamide becomes the continuous phase (between 30 and 40% polyamide) as a result is obtained an effective dissipation of the impact energy.

Fig. 1: Resilience Izod (23 ° C) as a function of PA6 content

Fig. 2: Performance of the "VICAT" (at 50 ° C / h) as a function of the PA6 content.

(a)

(b)

Fig. 3: SEM micrographs of  PA30 (a) and PA40 (b) samples.

Another evidence of the change that takes place between the properties of the blends containing 30% and 40% of PA6 emerges from the DSC diagram (Fig. 4). Indeed in cooling is observed that the phenomena of crystallization of PA6 occur for a content of at least 40% (from the sample PA40 in Fig. 4 a) and that in correspondence of such a composition will begin to highlight the occurrence of a multi peak fusion in the second heating scan (Fig. 4 b), which can be attributed to the fusion of two different crystal structures. The melting peak at a lower temperature is due to the fusion of crystals formed during cooling, while the second is related to the fusion of crystals formed during heating, the perfection of which implies higher melting temperatures.

Fig. 4: DSC paths in cooling (a) and second run in heating (b)

4. CONCLUSIONS 
The behavior of alloy PA6 / ABS with increasing content of PA6  at constant  content of the polybutadiene phase was studied through chemical-physical, morphological and mechanical Izod impact investigations.  It was observed that, for PA6 content lower than 40%, the alloys have a brittle behave, as a result of a high incompatibility at the interface between the components. For the content of polyamide in excess of 40%, the system shows a ductile and tough behavior, with good dissipation of the impact energy, the ability of the dispersed phase to interfere with the propagation of the fracture. Also the thermal behavior shows that between 30% and 40% of PA6, the polyamide phase is able to crystallize in cooling, indicating further that between these two compositions is obtained a phase inversion. 

References

1. J. Ren, H. Wang, L. Jian, J. Zhang, S. Yang. Morphological, thermal and mechanical properties of compatibilized Nilon 6/ABS. Journal of Macromolecular Science 47 (2008) 712-722.
2. V.J. Triacca, S. Ziaee, J.W. Barlow, H. Keskkula, D.R. Paul. Reactive compatibilization of blends of nylon 6 and ABS materials. Polymer 32 (1991) 1401-1413.
3. G. Humme, F. Fahnler, D. Neuray, K.H. Ott, P Tacke. Impact-Resistant Polyamide moulding compositions. Bayer Aktiengesellschaft US Patent n. 4,221,879 - Sep. 9 1980.