Molecular motion and transitions in solid tripalmitin measured by deuterium nuclear magnetic resonance

Deuterium nuclear magnetic resonance (NMR) quadrupole echo spectra of deuterated acyl chains and the glyceryl moiety of tripalmitin were found to depend on the crystal form. At 20°C, which is below melting points, line shapes indicate that molecular motions in theβ form (triclinic subcell) are more restricted than inβ′ (orthorhombic) orα (hexagonal). Motional rates in excess of about 20 kHz are responsible for the line shapes. Spin-lattice relaxation, sensitive to motional frequencies in the tens of megahertz range, is much faster for methyl (CD₂) groups inα orβ′ than inβ, indicating that fast motions are also governed by crystal form. General theoretical considerations suggest that motion of methylene groups is dynamically heterogeneous and that motion of methyl (CD₃) groups may be averaged by motions other than rotation about the terminal C-C bond. The isothermal solid-state transition fromα toβ, induced by increasing the temperature to 35°C, was accompanied by NMR lineshape changes consistent with immobilization. The reversible transition ofα to “sub-α” upon cooling, accompanied by orthorhombic-like Bragg spacings and other changes in the X-ray pattern and by corresponding changes in the infrared spectrum, also produced a marked restriction in NMR-detected mobility of the kind seen inβ′ relative toα. The advantages of²H NMR for studies of motions and transitions in solid glycerides are discussed. Presented at the 80th Annual Meeting of AOCS in Cincinnati, May 1989, and at the 81st Annual Meeting in Baltimore, May 1990.     

Modeling of structural reaction injection molding. Part II: Comparison with experimental data

A flow channel for experimental modeling of the structural reaction injection molding (SRIM) process, for producing composites with a sandwich‐like structure, has been designed and constructed. It consists of a thin rectangular box, in which the reinforcing glass fabrics with different permeabilities are positioned parallel to each other. The core layer is a thick, porous mat. Location of the other denser and thinner reinforcing materials into the flow channel was symmetrical with respect to the spacer mat. The channel has transparent walls for observing propagation of the impregnation front in the spacer mat and in the reinforcing dense layers. Development of the impregnation front during filling the flow channel and the pressure profile in the gate were measured for non‐foaming reactive polyurethanes. Enough good correspondence between the calculated and experimentally observed flow front position and pressure profiles was obtained.     

Aachen Technology Overview of 3D Textile Materials and Recent Innovation and Applications

Applied Composite Materials - This paper provides an overview of the recent definition, technologies and current trends regarding 3D fabrics. In this paper a definition of 3D fabrics, including...