Mechanical properties decay and morphological behaviour of biodegradable films for agricultural mulching in real scale experiment

The use of plastic materials in agriculture causes the serious drawback of huge quantities of waste. The introduction of biodegradable materials, which can be disposed directly into the soil, can be one possible solution to this problem. Biodegradable materials are actually innovative materials; therefore, their physical properties must be evaluated in relation to their functionality during the use in field. In the present research results of experimental tests carried out on biodegradable films used in strawberries protected cultivation are presented. The decay of some relevant physical parameters of biodegradable films during the cultivation period was monitored by laboratory tests (SEM analysis, mechanical tensile tests and infrared reflectance spectroscopy). Infrared spectroscopy clearly indicated that the mechanical degradation starts from the starch component of the material. Tensile tests showed that the value of elongation at break of biodegradable materials decreased in some cases by 300% after 10 days of field application.     

The crystal and molecular structure of the tetraethylammonium salt of tetrahydridopentadecacarbonyltetrarhenate(2−) in two crystallographic forms

The structure of the title compound, (NEt₄)₂[H₄Re₄(CO)₁₅], is reported in two crystallographic modifications, I and II. Both forms axe monoclinic and the cell constants are as follows: I, a 11.355(2), b 21.204(4), c 17.416(3) Å, β 94.15(2)°, space group P2₁/c; II, a 21.831(4), b 17.584(3), c 11.446(2) Å, β 96.02(2)°, space group P2₁,/n. Two sets of 3042 (I) and 2870 (II) independent diffraction intensities, collected by counter methods, were used for the solution and refinement of the two structures. The final conventional R factors have values 5.5% (I) and 6.3% (II), respectively. The crystal packings are compared, showing different conformations of the (NEt₄)⁺ cations. The anions contain a tetrametal cluster formed by an isosceles triangle plus an apically bound metal atom; the carbonyl groups are all terminally bonded to the rhenium atoms. Some differences, present both in the metal atom clusters and in the carbonyl dispositions, are discussed and compared with a third, previously reported, crystallographic modification of the same compound.     

Path integrals and linear canonical transformations

For a system withN bosonic or fermionic degrees of freedom I calculate the coherent state propagator, i.e. the matrix element between coherent states of the evolution operator, for a general quadratic Hamiltonian plus a source term, using the holomorphic form of the path integral. The analysis and the result obtained are used to discuss the transformation properties of the path integral for linear canonical transformations (Bogoliubov-Valatin trfs), a preliminary to the formulation of a geometric theory of path integral quantization.

     

Analytical algorithm for molecular modeling

A molecular modeling procedure, based on internal coordinates and strictly analytical even in the most intricated cases, is described. Internal coordinates, always nonredundant, become mutually independent and can be varied without constraints. Structural refinement from diffraction data (Least-square method, LS) can be done using the classical Gauss-Newton approach and avoiding Lagrange multipliers. A comparative test done using published data has shown that while the new method gives rise to a structural refinement in perfect agreement with the known structure, the traditional methods (z-matrix and constraints based) does not work.     

Crystal structures of rhodacyclopentane derivatives

Two complexes containing a rhodacyclopentane ring, viz. (acac)Rh(C₆H₈)(py)₂ and (acac)₂Rh₂(C₆H₈)(PPh₃) have been studied by X-ray diffraction. The ring forms through oxidative coupling of two allene molecules giving the structure A with trivalent, octahedrally-coordinated rhodium. In the second complex the unsaturated hydrocarbon part is also π-bonded to another Rh atom, and one acac group acts as a five-electron donor.     

Conformation of cyclic disulfides: The twinned layered structure of (1R,2S,7R,8S)-1,2,7,8-tetrahydroxy-4,5,10,11-tetrathiacyclododecane

The title compound C₈H₁₆O₄S₄ (TTCD) has been synthesized and its crystalline water adduct TTCD·H₂O studied by single-crystal X-ray diffraction. TTCD molecules sandwich water molecules, giving rise to two-molecule layers (bilayers) ofP2₁/b symmetry which gain remarkable rigidity because of their hydrogen bonds. In their turn, bilayers are piled according to four different structures having equivalent inter-bilayer H bonding and the same nonprimitive unit cell of lattice parametersa=4.893(2) (unique axis),b=15.110(6),c=74.30(2) Å, and=90.00(2)°. The crystal is twinned by merohedry with the four structures in comparable amounts. The relationship of the solid-state conformations to the UV absorption spectrum in solution is also discussed.     

Reactive blending of bioaffine polyesters through free-radical processes initiated by organic peroxides

Reactive polymer blending of poly(β-hydroxybutyrate) (PHB) and its valerate copolymers (PHBV) are reported, following two different methodologies, namely polymerization of rubber inclusions in the preformed matrix or reactive melt blending of preformed polymers. As second phase, poly(butyl acrylate) (PBA) and polycaprolactone (PCL) are used. The results of spectroscopic, thermal, mechanical and morphological analysis indicate the existence of chemical interactions between the blend components. Such interactions are also responsible of a drastic change in the morphology.     

Conformations of cyclic disulfides: The crystal structure of (1RS,2RS,7RS,8RS)-1,2,7,8-tetrahydroxy-4,5,10,11-tetrathiacyclododecane

The racemic form of the title compound C₈H₁₈O₄S₄ (TTCD), a twelve-membered cyclic disulfide, has been synthesized and studied by X-ray diffraction. TTCD·H₂O crystallizes in a multiply twinned pseudo-monoclinicC-centered lattice. For convenience aC-centered triclinic unit cell was chosen of dimensionsa=33.855(3),b=5.534(1),c=14.836(2) Å, =90.05(1),=94.76(1), =89.22(1)°,V=2769(1) ų,Z=8, space groupC¯1. The structure, solved by direct methods, was refined to anR of 0.063, using 2769 observed reflections. The two crystallographically independent TTCD molecules in the unit cell have very similar conformations. The distortion from the pseudomonoclinic symmetry is discussed in relation to the hydrogen bonding network.