Spotlight 2002 Abstracts
Paper Science EngineeringCELLULOSE MICROFIBERS AS REINFORCEMENT IN HIGH PERFORMANCE ENGINEERING THERMOPLASTICS
Deepanjan Bhattacharya and William T Winter, Cellulose Research Institute, SUNY-ESF, Syracuse, NY-13210.
Cellulose obtained from bagasse was broken down into microfibers (MF) through a sulfuric acid hydrolysis and a 2-stage homogenization process. The surfaces of the resulting MF were chemically modified with Maleic anhydride through a heterogeneous phase reaction. The success of this reaction was confirmed by Fourier transform infrared spectroscopy (FTIR) and NMR studies using a HR/MAS (High-Resolution Magic-Angle Spinning) probe as well as CP/MAS measurements. Wide-angle X-ray diffraction studies (XRD) confirmed that the esterification reaction was restricted to the crystal surfaces. The carboxylic acid content on the surface of the MF was determined from pHmetric titrations. Thermogravimetric analyses (TGA) of the cellulose MF revealed significant improvements in their thermal stability and extent of degradation upon surface modification. A kinetic study of the thermal degradation process revealed that while bagasse and cellulose crystals followed a first order reaction, the degradation of surface modified crystals were more complex. These surface modified cellulose MF could serve as excellent reinforcing filler particles in engineering thermoplastic composites. Preliminary studies of the reinforcement of poly(methylmethacrylate) with cellulose MF have yielded encouraging results
Asif Hasan and Dr. Steven Keller (co author and faculty member), Doctoral Student, Paper Science Engineering Department, 418 Walters Hall, SUNY college of environmental science and forestry, Syracuse, NY-13210.
Non-uniformity defects may occur in paper and paperboard as a result of the hydrodynamics in the headbox and forming zone of a paper machine. Since their occurrence is related to the machine speed, streaks may appear stationary or mobile, they may be intermittent or continuous and may occur at regular or irregular intervals across the machine width. For this reason, there is substantial interest in characterizing the various forms of streaks (not limited to grammage variation) determine their origin and provide preventive measures. A novel approach pursued by Kellomaki, Keller, Pawlak and Sung  was able to separating the static and stochastic components of spatial variability data and thus provide information about the scale of features, e.g. flocs or streaks, as function of position within the data array in one direction. The local energy map can be decomposed into two different parts that contains all the energy related to the static mean grammage profile and local stochastic variability. In this work, the major focus was: classification and measurement of the various forms of streaks in addition to grammage non-uniformity. The primary objective was to reduce massive amount of data into meaningful indicators that can be used to distinguish the streak defects and identify their origin. Streak defects are always not inflicted by grammage variation but may also result from filler distribution. No procedure to characterize this type of streaks is available so far. Ash imaging has the potential to become a viable method to spot the filler distribution streaks. This work was limited to paper samples with a grammage value of less than 120 g/m2-which makes it specific to the light to medium density paper.
1. Kellomaki, Markku., Pawlak, Joel. J., Sung, Yong-Joo., and Keller, D. Steven., “Characterization of Non-stationery Structural Non-uniformities in Paper,” in the12th fundamental Research Symposium Keble College, Oxford, UK(2001).
Yong Joo Sung and D. Steven Keller, Faculty of Paper Science and Engineering, 417 Wallters Hall, SUNY-College of Environmental Science and Forestry, Syracuse, NY 13210.
The local variation of the paper structure is usually contained not only stochastic variation but also the periodic variation. Since the periodic variation of paper structure can cause a significant defects in the end use paper properties such as the optical appearance and printability, the evaluation and determination of the periodic pattern is very important to identify the origin of the periodic variation and to remove or minimize the variation.
In this poster, the systematic method for detecting, analyzing and identifying the periodic variation in the paper structure. The spatial distribution of the fundamental local structural properties such as the local thickness map, the local grammage map, the local density map and both surface roughness map were obtained by using a storage phosphor b radiography imaging system and the twin laser profilometer(TLP) instrument. Although the periodic variation can be detected by naked eye, the more detailed information of the periodic variation can be obtained by using two-dimensional fast Fourier transform (FFT). This analysis method could isolate the periodic variation from the stochastic variation and make it possible to visualize the original pattern for each periodic variation. The applications of this method to the real commercial paper are presented.
Haowen Xu and Dr. D. Steven Keller, Faculty of Paper Science and Engineering, 418 Walters Hall, SUNY College of Environmental Science and Forestry, Syracuse, NY13210.
The rheology of coating colors at high solid contents and shear rates is of increasing importance as coating machine speeds continue to increase since as a general rule, coating color should be applied at as high solid as possible. This is to minimize the drying cost as well as improve the surface properties of coated paper. Coating pigment are mineral particles with diameters in the range of 0.5-2.0mm. These are used to impart high smoothness and gloss to the paper surface and improve the printing qualities. The suspension of coating pigments usually exhibits complex non-newtonian flow behavior when subjected to high shear rate and high solid content. In some cases, shear thickening (dilantancy) has been observed. This has been correlated with the non-uniformity of coating surface, poor runnability on the coater and other problems occurred in pumping, screening and delivery systems. A thorough understanding of the rheological behavior of pigment suspension in shear thickening regimes could provide essential information about the performance of coating color in the coating process and thus give an insight into the design of coating delivery and recirculation systems.
The flow properties of concentrated calcium carbonate dispersions used as paper coating pigments have been investigated in ramp and transient shearing flows using a Couette flow viscometer. The dispersion was composed of stabilized calcium carbonate particles suspended in water with volume concentration in the shear thickening regimes. Ramp test results indicated a shear thinning region at low shear rates and then a discontinuous or gradual shear thickening region after the critical shear rates. The samples which exhibit discontinuous shear thickening behavior in ramp test were found to “jam” or solidify in the transient rheological test, which might indicate an irreversible change in the microstructure of suspensions. The viscous energy dissipated prior to collapse was found to be constant, regardless of the applied shear rates. The samples with a gradual or weak shear thickening region also show a gradual increase of shear stress as a function of time, which could be associated with the formation of transient hydrodynamic clusters. The stress recovery curve for different shear rates in the shear thickening region could be collapsed into a master curve if plotted against strain.