Manufacturing of starch-based materials using ultrasonic compression moulding (UCM): toward a structural application.

An experimental study of the ultrasonic compression moulding (UCM) to manufacture biobased composites made of semicrystalline starch powders and softwood fibres is described. The main objective was to assess the potential of using this fast and economical processing technique to elaborate a 100% biobased composite which might substitute more usual polymer materials for structural applications. The starch powder was chosen as raw material for the matrix while the reinforcement was made of softwood fibres. Tablets made of starch only and composite beams were processed under different conditions and characterised by several techniques. Three types of starch powders and two types of fibres were used as raw materials. A morphological and crystalline analysis was carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The native semicrystalline structure of starch granules was not totally preserved so as to obtain a homogeneous material. Diametral compression tests on tablets were performed to improve the processing route and obtain the materials with the best properties. Bending tests were used on composite beams to quantify the mechanical properties and study the effects of the processing parameters. The optimum processing parameters were defined and allowed obtaining a matrix for which the flexural strength reached 21 MPa. Mechanical properties were improved when fibres were added into the matrix: three-points bending tests showed a Young's modulus of 6 GPa, a flexural strength of 75 MPa and a flexural strain at break of 6% for a bulk density of 1.25. Considering these results, UCM appears to be a promising process to design a 100% biobased composite with mechanical properties comparable to those of classical discontinuous fibre composites.

Comparison of Hektoen and Salmonella-Shigella agar on 6033 stools of human origin submitted for routine isolation of Salmonella sp. and Shigella sp.

From 1989 through 1991, 6033 stool specimens from patients at Orleans Hospital (France), were cultured for enteric pathogens. Hektoen agar (HE) was compared with Salmonella-Shigella agar (SS) after direct streaking and after overnight enrichment in Mueller-Kauffmann broth. Yersinia strains were not computed. Seven strains of Salmonella serotype Typhi were isolated, on both media, and excluded from computations for discussed reasons. Out of a total of 9 Shigella strains, HE isolated 9 and SS isolated 7. No statistically significant difference appeared about isolation of non-Typhi Salmonella strains (127 vs 114 from direct streaking, 237 vs 243 after enrichment). Predictive values of suspicious colonies were not statistically different. Numbers of false positives were not different, except for black centred colonies of the direct streaking (231 on HE vs 186 on SS, p less than 0.05). The skill of technologists was not taken into account but was found likely to be more accurate on SS agar. This data suggest that, since the frequency of Shigella sp became much lower, the differential of efficiency of HE vs SS agar is no longer obvious in human medical routine.