JEC COMPOSITES MAGAZINE - Issue #41 - June 2008 - 69

KNOW-HOW system – here, the screw/barrel system of extrusion and injection moulding devices. The system (figure 5) consists of a square pitch screw placed in a transparent cylindrical barrel made of polymethylmethacrylate (PMMA). The screw is actuated by an electrical motor (speed max 44 rpm, torque max 9 Nm) and conveys the transparent viscous fluid to a tube in closed circuit. An aperture is provided to inject fluorescent particles or a small amount of a masterbatch, prepared by mixing fluorescent particles in with the same fluid evolving through the circuit. The fluorescence excitation is assured by a laser sheet (Ï = 532 nm) passing by the axis of the cylindrical system. Four CCD cameras (Basler A301F) equipped with filters to subtract the source light are mounted on a mobile support around the Visiovis. They are aligned parallel to the screw/barrel system and perpendicularly to the geometrical plan of the laser sheet. Each camera can record up to 80 images per second, with a resolution of 640 x 480 pixels and a depth of 8 bits. The acquisition of images, performed in the dark to visualize only the fluorescent particles, is triggered by an electromechanical output transducer (switch). In front of the cameras, on the opposite side of the laser sheet, an optical fibre collects on-line the signal emitted by the fluorescent particles. The fluorescence signal is analyzed by a spectrofluorimeter (USB2000 + miniature fibre optic spectrometer, Oceanoptics) and the spectra are regularly recorded. The geometrical parameters of Visiovis (table 1 and figure 6) are comparable to the design parameters of the metering section of the devices typically used for extrusion and injection moulding, characterized by a shallow channel and a pitch value fairly similar to the diameter value [14]. Tab. 1: Visiovis geometrical parameters vs. design parameters of industrial device metering section Fig.6: Schematics of a screw/barrel system The transparent fluid used to model a molten thermoplastic polymer (or an uncured thermoset resin) is polydimethylsiloxane (PDMS) (Roth, Germany), available with different viscosities. Fillers are selected for their potential application with plastics, their natural luminescence or the possibility of modifying their emission properties: 1) GT5700 (GloTech, New Zealand), a phosphorescent rare earth aluminate pigment. This commercial micro-sized pigment (45-55 μm) is easily excitable by UV-visible radiation. 2) Cloisite® Na+ (hydrophilic clay) and Cloisite® 30B, Cloisite® 10A, Cloisite® 15A (organically-modified clays) (Southern Clay Prod., USA), commercial clays successfully photo-functionalized by cation exchange with Rhodamine 6G perchlorate (Sigma-Aldrich, France). Some early results Geometrical parameters Barrel diameter (Db) Screw root diameter (Ds) Screw pitch (2π·Ph) Channel depth (H) Channel width (W) Screw angle, measured in the middle of the channel (φ) Aspect ratio (λ) Curvature (ε) Torsion (α) Tan(φ) where φ=α/ε Visiovis 40 mm 30 mm 40 mm 5 mm 34.6 mm 20° 6.9 0.44 0.16 0.33 Metering section [14] 120 mm 110 mm 120 mm 5 mm 109 mm 18.37° 21.8 0.15 0.05 0.33 The serial images acquired by the cameras (two examples are shown in figure 7) are useful to evaluate the temporal evolution of nanofiller distribution in the volume of fluid comprised in between the screw flights. We implemented two Matlab programs which process the serial images acquired with photo-functionalized clays on the basis of, respectively, the standard deviation of image luminosity and the Fourier transformation of textured images (Figure 8). The first processing step calculates, for each picture of a given series, the local values of the standard deviation of image luminosity, integrates these values on the whole surface of the picture and plots the logarithm of the integral standard deviation as a function of the number of images (i.e. the number of screw revolutions). The second processing step codifies a textured image by the frequencies of an elementary textural unit (e.g. a spiral or twisted fluorescent volute in a homogeneously black matrix). The Fourier transformation of an image composed of discrete pixels produces a discrete spectrum of frequencies, delimited by a minimum and a maximum frequency value. The minimum value corresponds to the physical dimension of the picture (minimum of details); the maximum value corresponds to the intrinsic frequency of pixel repetition (maximum of details). The higher the main coding frequencies, the finer the texture of the numerical picture: an image which is finely textured is coded by high frequencies since the No41 May 2008 / JEC Composites Magazine
JEC COMPOSITES MAGAZINE - Issue #41 - June 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #41 - June 2008
