Bert J. Kip

A facility location allocation model for reusing carpet materials

Re-using the huge quantities of carpet waste that are yearly generated has become a must. A facility location–allocation model for the collection, preprocessing and redistribution of carpet waste is presented. This model differs from other mathematical models for supporting the design of the logistic structure of reuse networks among others in a completely free choice of the locations for preprocessing and in explicitly taking into account depreciation costs. Two applications of the model, one in Europe and one in the United States of America, are described.

Confocal Raman Microspectroscopy: Theory and Application to Thin Polymer Samples

Raman microspectroscopy can be used effectively to study very small samples or to study small areas within a transparent sample. With the application of the technique of confocal microscopy to a Raman microscope, the depth resolution of the instrument can be enhanced considerably. Confocal microscopy uses a pinhole, placed in the back image plane of the microscope objective, to block light from outside the focal plane. In this way the signal from the small volume element one wants to study can be better separated from the signals arising from the surrounding material. In this paper we show that the performance of the confocal Raman microscope can be described satisfactorily by geometrical optics. Furthermore, we have performed measurements to determine the depth resolution of our system for different combinations of objectives and pinholes. Finally, we report on the applications of this technique to different polymer systems, such as multilayer foils, fibers, and fiber composites.

Raman Imaging of Heterogeneous Polymers: A Comparison of Global versus Point Illumination:

Two alternative methods of Raman imaging, via global (wide-field) illumination and via point illumination in combination with confocal light collection, have been applied to the study of heterogeneous polymer systems. From the results obtained it becomes apparent that the fluorescence inherent to most polymer systems severely limits the use of global illumination. Furthermore, the lack in depth resolution in Raman imaging by global illumination ruled out this method for the study of bulk polymer samples. Also as a consequence of the absence of depth resolution, the global illumination technique appeared more vulnerable to artifacts arising from scattering effects due to the sample geometry and fluorescence. Hence, for a general application of Raman imaging to the study of polymer samples, Raman imaging by point illumination in conjunction with confocal light collection is the method of choice

Investigation of melamine-formaldehyde cure by Fourier transform Raman spectroscopy

Abstract Fourier transform (FT) Raman spectroscopy has been used for characterization of melamine-formaldehyde (MF) resins. Band assignments were based on a combination of literature band assignments, a study of the Raman spectra of model compounds and well characterized MF adducts and resins. The triazine ring breathing band at 975 cm −1 and the C-H stretching bands around 3000 cm −1 can be used as internal reference bands in the Raman spectra of MF resins. It is shown that FT-Raman spectroscopy, in combination with 13 C nuclear magnetic resonance and liquid chromatography can bring further elucidation on the methylolation and ether- and methylene-bridge formation in (cured) MF resins.

An in situ Raman spectroscopic study of the degradation of PVC

Raman spectroscopy has been used to study the in situ degradation of PVC in nitrogen and in air at different temperatures. After a rapid initial increase in the number of polyenes, the rate decreases and eventually the concentration becomes constant while the rate of dehydrochlorination is constant over the same period. These results are interpreted using a ‘steady-state’ approach. After a certain time the rate of formation of polyenes equals the rate of consecutive reactions of polyenes, i.e. cross-linking and oxidation. A higher degradation temperature and a higher oxygen concentration both result in a lower steady-state concentration of polyene.

Determination of the Local Temperature at a Sample during Raman Experiments Using Stokes and Anti-Stokes Raman Bands

Sample heating due to high incident laser power in Raman experiments on (industrial) polymers and catalysts can easily lead to unwanted changes in morphology or desorption of surface species. Therefore temperature of the sample at the laser spot was studied by determining Stokes and anti-Stokes Raman intensities. Temperature can normally be determined within an accuracy of about 5 K, although for samples having nothing but Raman bands above 1000 cm−1, the anti-Stokes lines are very weak and accuracy of temperature determination decreased drastically. For most of the samples studied in the macro-Raman setup, powers up to 250 m\V could be used without measurable heating. In the micro-Raman setup heating started earlier due to higher focusing.

Micro-Raman imaging of heterogeneous polymer systems: General applications and limitations

This article assesses the use of micro-Raman imaging with respect to polymer science. This relatively novel technique allows, at high spatial resolution, the acquisition of chemical and morphological information over an area of a sample. Using Raman imaging by confocal laser line scanning, a wide range of problems in polymer analysis has been studied to outline the capabilities and limitations of the technique. Three ternary polymer blends consisting of polypropene/polyethene/ethene-propene copolymer, polybutyleneterephthalate/polycarbonate/very low density polyethene, and styrene-co-acrylonitrile/styrene-co-maleicanhydrate/poly-2,6-dimethylphenylene oxide were studied with regard to compositional and morphological heterogeneities. In a binary polymer blend consisting of two different acrylate monomers, the refractive index profile established after artificially induced diffusion of the main components was determined from the concentration gradients. The distribution of unreacted free melamine in a cured melamine-formaldehyde resin was analyzed. Furthermore, the general structure of a composite sample consisting of polyethene fibers in an epoxide matrix was studied. Raman imaging proved suitable for the characterization of heterogeneities in composition and morphology on a size scale equal to or larger than 1 μm. In this sense, the technique helps to close the gap between infrared microscopy, with its comparatively poor spatial resolution, on the one hand, and transmission electron microscopy, with its limited chemical information, on the other hand. For heterogeneities on a submicron scale, the value of the technique is limited to the determination of average information. When combined with curve fitting, Raman imaging permitted us to determine the composition of the polypropene/polyethene/ethene-propene copolymer blend with an accuracy of 5–10%. The main limitations to micro-Raman imaging of polymer systems based on the confocal laser line scanning technique have been identified as the destruction of the samples due to insufficient heat dissipation of the high-incident laser power, interferences due to fluorescence, and the stability of the instrumentation during long collection times required for good signal-to-noise ratio spectra of weak Raman scatterers.

A quantum chemical study of the degradation and the maximum polyene length in PVC

Abstract The semi-empirical MINDO/3, AM1 and MNDO-PM3 methods were employed to study the stability of polyenes, polyenyl cations and polyenyl radicals. Both cations and radicals were subjected to computation since the elimination of HCl from PVC might proceed according to an ionic or radical mechanism. We subsequently investigated the effect of additional alkane chain ends, as well as PVC-like chain ends to both ends of the polyene sequence, in order to mimic degraded PVC better. The results are discussed in relation to the experimentally observed polyene length distribution in degraded PVC, as revealed from UV-Vis and Resonance Raman Spectroscopic data. The following conclusions may be drawn from the data presented. The MINDO/3 method has to be rejected. From the calculations, which basically refer to the molecules being in the gas phase, it was concluded that the formation of radical intermediates during polyene formation is much preferred (energetically) as compared to the corresponding ionic species. However, several researchers have suggested that the ionic process is preferred in solid PVC (‘solvation effect’); for solid PVC hard experimental evidence is still lacking with respect to either of the two mechanisms. The introduction of saturated chain ends markedly influences the energetics and the stability of the polyenes. HCl abstraction from an intact PVC chain was calculated to be about as probable as HCl abstraction adjacent to a polyene sequence. Calculations on polyenes with PVC-like chain ends do not give any indication that there is a maximum polyene length after which further elimination of HCl becomes less probable from an energetic point of view. The calculated data presented show no evidence for a finite polyene length, and thus do not support the unzipping mechanism. We propose a new one-step unzipping mechanism.

Determination of free melamine content in melamine-formaldehyde resins by Raman spectroscopy

We have shown that Raman spectroscopy can be used to determine the free melamine content in melamine-formaldehyde (MF) resins. In contrast to the conventional liquid chromatography method, the Raman spectroscopic method can be directly applied to cured resins without sample preparation. The necessary assignments of bands were supported by theoretical analysis of Raman frequencies. In addition, Raman imaging was used to determine the homogeneity of the free melamine content in cured MF resins.

Role of an active environment of use in an environmental stress crack resistance (ESCR) test in stretched polyethylene : A vibrational spectroscopy and a SEM study

Abstract Characterisation of the role of an active environment of use in an industrial Environmental Stress Crack Resistance (ESCR) test has been carried out during the tensile deformation of polyethylene samples. We intended to map the presence of the active environment within the material using Raman and infrared spectroscopy. We found Raman not suitable for the detection of this environment inside the sample while by IR the environment seemed to be predominantly present within the transition fronts of the material. A stress-induced environment diffusion mechanism is suggested. By scanning electron microscopy (SEM) differences in the deformation process between drawing in air or in detergent became apparent. These results suggest that the environment penetrates into the sample during the necking process, stabilising crazing. At the molecular level it is likely that chain slip and unravelling of molecular disentanglements are facilitated. All these observations may also be operative during the ESC phenomenon as samples are subjected to stress, resulting in crazing.