An on-line technique of sensing CO₂ concentration in molten polymers in process extruders was studied with a near infrared (NIR) spectrophotometer. The NIR spectra were acquired at an optical flow cell where the sample solutions were forced to pass through before entering an extruder die. Experiments were carried out for a polypropylene and CO₂ system at 473-503K and ∼9.4MPa. The CO₂ concentrations were evaluated from the NIR absorbance data after baseline corrections. The plots of the absorption peak area against the apparent CO₂ weight fraction determined from the CO₂/polymer feed ratio were found to show a linear relationship, suggesting the applicability of the Beer-Lambert's law in terms of weight fraction base. Further experiments at higher CO₂ concentrations clearly exhibited saturation behaviors in the plots of NIR absorption peak area against the apparent feed concentration, which meant that below the saturated concentrations the NIR absorption could provide the correct CO₂ concentration by using the Beer-Lambert's law and the saturated solubility. Thus it could be noted that NIR spectra can be a useful technique for quantitative analysis of CO₂ concentration in molten polymers.

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This study examines a new material recycling technology by the kneaded co-extrusion of sintered waste resin pellets added to a molten polyethylene (PE) stream in an intermixing corotating twin screw extruder. Polystyrene (PS), nylon-6 (PA) and ABS were used as the waste resin pellets to be combined with the PE matrix. Test pieces for measuring tensile stress and bend strength were molded from material extruded under different kneading conditions of kneading temperature, residence time and PE content. Good physical properties were obtained at longer residence times and higher kneading temperatures. For the PS/PE system extruded at 230°C and 33rpm, the tensile stress of molded samples reached 15MPa with PE content ranging from 20∼50wt%. For the PA/PE system, tensile stress and bend strength could be increased by about 1∼3MPa with the addition of ADMER as a compatibilizer. Optical micrographs of cross sections showed that better physical properties correlated with better phase mixing. The phase mixing between components of the blends was quantified by dynamic viscoelasticity.

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Resin-coated paper (RC paper) which is manufactured by melt-extrusion of a coating of polyethylene resin onto both sides of the paper base is mainly used as a support for imaging materials such as photographic paper. The surface smoothness of RC paper is an important property and it is necessary to quantitatively define the surface smoothness. We thus analyzed the surface roughness of RC paper and sharp dents (pits) or “pear skin” generated on the surfaces of RC paper. We found that the surface roughness calculated by a flattening estimation using a leveling theory for a liquid coating corresponded well with the experimental values. Also we found that the observed density of surface pits agreed well with those obtained by using an index based on the flattening estimation model where the pits are related to deep vacancies which still remain on the surface of the base paper even after coating the base paper. These results support the validity of the flattening estimation model and the pit generation model where the pits are considered to be projections of the volume of deep vacancies remaining on the surface of the base paper. The pit estimation model can be widely applied by using the index correcting the elastic behavior of a resin.

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