The following image shows POLYPROPYLENE/COSMOS-RICE(30%) granules that have been realized to create the composites

This work allows to evaluate of the effects of COSMOS RICE (CR) on structure and properties of melt compounded polypropylene (PP) based composites by means of extensive structural, physical (mechanical testings) and thermal analyses. In terms of comparison CaCO3 and COSMOS (C) (from commercial colloidal silica, see based PP composites, produced and analyzed in the same conditions,  have been also considered.

The difference with COSMOS technology is also related to the use of COSMOS-RICE containing soluble salts, that were not washed from inert.

The results of this study has been very recently published and are freely available at:

The effectiveness of filler dispersion can be measured indirectly from mechanical properties evaluation. Figure 1 reports the trend of normalized tensile elastic modulus varying CR content and melt compounding speed. In order to have a more direct comparison with pristine polymer properties, normalized values obtained by the ratios between composites and matrix ones has been used. As already specified the values regarding COSMOS based composites have been recovered from a previous publication and used in terms of comparison [Besco, S.; Brisotto, M.; Gianoncelli, A.; Depero, L.E.; Bontempi, E.; Lorenzetti, A.; Modesti, M. Processing and properties of polypropylene-based composites containing inertized fly ash from municipal solid waste incineration. Journal of Applied Polymer Science 2013, 130, 4157–4164].
Tensile modulus increase can be observed as a function of CR content, up to a maximum value corresponding to about +100% for PP/CR 30wt.% composites (100rpm, that is the screw speed variation) if compared with pristine PP. Moreover,  regarding PP/CR composites, considering experimental error, screw speed variation seem to have negligible effects on stiffness, leading to only slightly higher values for the samples obtained at 100rpm.
Moreover, from the comparison between rice husk silica based (CR) and colloidal silica based (C) inertized fly ash fillers there are not remarkable differences to be reported considering experimental error.
Regarding the comparison with CaCO3 based formulation it can be observed that C and CR based composites (30wt.% filler content, 100rpm) show comparable values in terms of stiffness increase with respect to pristine polymer performances.
A very similar trend can be observed for normalized flexural elastic modulus, as reported in Figure 2 as a function of filler composition (C, CR, CaCO3), filler content (5, 15, 30 wt.%) and compounding screw speed (50 or 100rpm). If compared with tensile modulus analysis the maximum increases reached with for the different compositions are lower on average, even if for PP/C 30wt.% (100rpm) composite a +100% can be observed with respect to pristine PP. Moreover, in this case the CR based composite shows values significantly lower than C and CaCO3 based ones obtained in the same conditions.
The plot in Figure 3 refers to the trends evaluated for maximum flexural stress (normalized) varying samples composition and processing conditions. A clear increase can be evidenced as a direct function of filler content both for C and CR based samples, even if with values well below the ones observed for elastic moduli. The most remarkable result concerns with PP/COSMOS 30wt.% (100rpm) sample, that show a value about +20% higher than the one measured for C and CaCO3 based composites obtained with the same formulation and using the same processing conditions.
Moreover these results confirms the little or negligible influence of processing conditions on the macroscale mechanical behavior of the CR based composites.
Regarding thermal properties, normalized melt crystallization temperature behavior as a function of formulate and processing parameters was also calculated. The parameter has been obtained calculating the ratio between composite and matrix crystallization temperatures for each considered sample. A proportional increase up to about +10% (corresponding a relative increase of +18°C if compared to pristine PP) can be observed proportionally with the increase of CR content, while for colloidal silica based materials (C) the increase appears much more contained. Regarding CaCO3 based composites (30wt.% filler content, 100 rpm) they show the lowest increase in melt crystallization temperature if compared with the similar C and CR based. The increase of crystallization temperature can have remarkable effects on manufacturing costs regarding injection molding processes due to the possibility of reducing cooling step and hence to shorten production cycles.
The thermal stability of the composites has been evaluated using thermal-gravimetric analysis and comparing the temperatures corresponding to the 50% of weight loss for the different samples. Also for this property a proportional increase with respect to filler content can be observed regarding CR based samples while, within experimental error, processing conditions don’t influence thermal stability as well. The comparison within CR and CaCO3 based materials (30 wt.% filler content) underline the higher stabilizing effect of the former, while C seems to show an intermediate behavior.

In summary it is possible to conclude that the new proposed filler (COSMOS-RICE), made on stabilized MSWI fly ash, after the application of a new low cost technology, can be used in the PP composites production, instead of calcite, allowing to preserve natural resources.



FIG.1 – Tensile modulus for CR, C and CaCO3 based composites varying processing conditions (normalized values).



FIG.2 – Flexural modulus for CR, C and CaCO3 based composites varying processing conditions (normalized values).

FIG.3 – Maximum stress (flexural) for CR, C and CaCO3 based composites varying processing conditions (normalized values).

This work was made in collaboration with University of Padova (prof. Modesti).

Many thanks to Vusapl and Velaworks (two Slovakian SMEs) for supporting the activity.

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