No abstract

Calcium carbonate (CaCO3) particles have been widely used in filling thermoplastics for different applications in automotive, packaging, and construction. No agreement has been reached in the research community regarding the function of CaCO3 for enhancing toughness of homopolymer polypropylene (HPP). This study was to understand the effect of different loading levels of CaCO3 on HPP toughness, including notched and unnotched impact strength. A batch mixer was used to thermally compound CaCO3 particles with HPP at loading levels of 10, 20, 30, 40, and 50 wt.%, followed by specimen preparation using an injection molding process. The mechanical properties of the composites, including tensile, flexural, and impact were characterized. The results indicated that tensile strengths decreased significantly with increasing loading levels of CaCO3 particles while the tensile and flexural modulus increased significantly with increasing particle loadings. The composite tensile properties changed linearly with increasing CaCO3 loadings. The notched Izod impact strength of the composites was sustained by adding CaCO3 particles up to 40 wt.% while the unnotched impact strength decreased significantly with the addition of CaCO3 particles. Different deformation mechanisms between notched (fracture propagation) and unnotched (fracture initiation and propagation) impact tests were proposed to be the reason.

No abstract

This study examined variation of stomatal density in two populations of Quercus petraea (Matt.) Liebl. and two populations of Q. robur L. from northwestern Turkey. Stomatal density was determined in fully expanded and dried leaf samples that were collected from trees under natural conditions. Stomatal densities of Q. petraea and Q. robur varied from 186 to 459 per mm 2 (mean value: 333 stomata per mm 2 ) and from 397 to 826 per mm 2 (mean value: 517 stomata per mm 2 ), respectively. Significant differences in stomatal density were found between these two oak species in Turkey as well as between populations within species. Strong and significant negative correlations were observed between stomatal density and leaf length within each species and across the species. While in Central Europe Q. petraea occurs in drier environments than Q. robur, in the present study Q. robur populations grow in more arid environments and have smaller leaves and a higher stomatal density than Q. petraea. Stomatal density had negative correlations with each of the other leaf characters apart from sinus width. In addition, the interspecific P ST value (0.48) for stomatal density was relatively high compared to the mean genetic differentiation calculated at eight microsatellite loci (F ST = 0.030), suggesting different local adaptations of populations. Further studies that include additional populations will be necessary to associate genetic variation at candidate genes with phenotypic and environmental variation.