2013 Volume 1
Cambridgepp 907-925Overview of Practical and Theoretical Aspects of Mineral Oil Contaminants in Mill Process and PaperboardsAbstractPDF
The paperboard industry is committed to consumer protection in food packaging and has assigned top priority to the issue of mineral oil hydrocarbons (MOH) as early as spring 2010. In this work, we have developed practical methods, using gas chromatography with a flame ionization detector (GC-FID) laboratory equipment, to characterize the level of mineral oil saturated hydrocarbons (MOSH) and aromatic hydrocarbons (MOAH) in European and North American newspapers, paperboards, and inks. As part of our validation protocol, several samples were analyzed by an external laboratory (ISEGA, Aschaffenburg, Germany) using Biedermann’s protocol and an average deviation of 6% for the MOSH and 17% for the MOAH was observed between ISEGA and our method. Using the reference Tenax migration method (EN, 14338), the hexane or heptane vapour transmission rate (HVTR) method was developed to measure the barrier efficiency within one day, showing a very good correlation; R2 = 0.80 to 0.92.
Much higher MOH concentrations in newspaper printed areas infer that printing inks constituents are the most likely source of MOSH/MOAH in recycled paperboard. When processing such raw material, the drying section is one of the paperboard making process steps that significantly reduces the MOSH and MOAH level. Although low or free mineral oil printing inks would be preferable, the use of functional barriers can significantly reduce the migration of MOSH/MOAH, whenever necessary. Mineral oil migration barrier efficiencies of about 90% were obtained using polymeric functional barriers applied at the mill with conventional coating equipment. Finally, a first attempt was made to theoretically model the migration of mineral oil through model polyacrylate functional barriers. The correlation between calculated (theoretical) and experimental hexane permeabilities seems reasonable and a predictive discrimination between good and bad barrier polymers appears possible for acrylate copolymers (R2=0.72) within foreseeable limitations with respect to chemical composition.
Extracted xylan from beech dissolving pulp and eucalyptus kraft pulp was precipitated on unrefined, bleached, once-dried softwood kraft pulp and sulfite pulp. The temperature, pH, ionic strength, xylan concentration, pulp consistency, and the dwell time were analyzed regarding their influence on the adsorption of xylan. Furthermore, handsheets were made to investigate the impact of xylan on the tensile strength and the tearing resistance of the paper. The swelling behavior of the fibers was of interest as well as the determination of the total and surface charge of the pulp.
The xylan content of the fibers could be significantly increased. The temperature, xylan concentration and ionic strength showed a large influence on precipitation. No significant change in the attachment of xylan between neutral and low alkaline level of the pH could be noticed. A higher pulp consistency, including a sufficient mixing during adsorption, is favorable. Xylan shows a large impact on the tensile strength of the softwood handsheets. The tensile index of the handsheets made of the softwood pulp and refined at 3.000 revolutions with a PFI mill could be increased by up to 38% compared to the reference sample. The xylan-modified samples also showed by trend a higher stretch at break of about 0.5%. This could be the result of a higher surface area and total charge of the fibers. Thus, enhanced swelling is caused leading to softer and more flexible fibers. These effects provoke a larger area in molecular contact. On the other hand, the trend of the tear index of the softwood handsheets with an increased amount of xylan declines stronger after a longer time period of refining.
Cambridgepp 929-944Paper-Based Blood Grouping; Exploring the Mechanisms of Red Blood Cell Agglutination in Antibody-Treated Paper via Confocal MicroscopyAbstractPDF
The recent invention of paper-based blood typing devices which are inexpensive, but also accurate and easily interpreted, has shown great promise for the future. Despite the efficacy of these devices, the underlying mechanisms responsible for how they function have remained largely unknown. This work illuminates these mechanisms by using the technique of confocal microscopy to delve into the behaviour of red blood cells at the micro-scale and view exactly what is happening as blood samples interact with antibody treated paper substrates. The underlying mechanisms responsible for the phase separation of red blood cells and plasma from whole blood on paper are elucidated for the first time, opening the door to future enhancements to such devices. It was revealed that the dominant mechanism responsible for the separation of whole blood into its respective phases was the physical entrapment of large red blood cell aggregates following their agglutination. Understanding these mechanisms and the effects of the paper structure makes optimization of paper-based blood diagnostics possible. Further investigations of optimal pore sizes, tortuosity or fibre size may lead to significant improvements in the sensitivity and accuracy of this important diagnostic platform.
Cambridgepp 967-989Gold Nanoparticles Paper as Surface Enhanced Raman Scattering (SERS) Platform for Bio-diagnostic ApplicationsAbstractPDF
We explored the sensitivity and selectivity of gold nanoparticles (AuNPs) treated paper as a generic SERS diagnostic platform to identify and quantify low concentrations of a specific (bio)analyte in aqueous solutions. The effects of gold nanoparticles (AuNPs) concentration on their adsorption and aggregation states on paper were explored. The surface coverage of AuNPs on paper scaled linearly with their concentration profile in solutions. The SERS performances of the AuNPs-treated papers were evaluated with a model Raman molecule, 4-aminothiophenol (4-ATP), and their SERS intensities increased linearly with the density of AuNPs on paper. To increase the SERS sensitivity, the retention and aggregation state of nanoparticles on paper was controlled by pre-treating paper with a series of cationic polyacrylamide (CPAM) solutions. The CPAM pre-treated paper produced a more uniform distribution of AuNPs compared to untreated paper. Higher surface coverage and aggregation of AuNPs on paper were favoured by CPAM solutions of higher concentration, charge density and molecular weight. The optimized AuNPs-CPAM paper showed a higher sensitivity and Raman enhancement factor (EF), which was almost an order of magnitude higher than the untreated AuNPs paper. After the SERS sensitivity towards the detection of model Raman molecule (4-ATP) was proven, the SERS selectivity of AuNPs paper was demonstrated by functionalizing the AuNPs with a model biomolecule platform consisting of biotin/streptavidin assemblies for the detection of antibody-antigen binding. The modification of antibody local structure due to the interaction with antigen was detected. Evidence of antigen binding was elucidated from the SERS spectra, confirming the presence of antigen. Reproducible spectra features were observed for the functionalized AuNP papers which were exposed to different concentration of antigen; the spectra intensity increased as a function of antigen concentration. The sensitivity and selectivity of AuNPs paper substrates as a low-cost and generic SERS platform for bio-diagnostic application was demonstrated.
Requirements for paper to be used as substrate for printed functionality were investigated. A recyclable, multilayer-coated paper substrate that combines adequate barrier and printability properties for printed electronics and sensor applications was developed. In this multilayer structure, a thin top-coating consisting of mineral pigments is coated on top of a dispersion-coated barrier layer. The top-coating provides well-controlled sorption properties through controlled thickness and porosity, thus enabling optimizing the printability of functional materials. The optimum barrier layer structure was investigated by studying the influence of latex type and amount in blends with different size and shape factor kaolin pigments. Highly aligned high shape factor kaolin improved barrier properties in general, but was found especially useful against organic solvents, which may degrade the latex. Dimensional stability and its influence on substrate surface properties as well as on functionality of conductive tracks were studied by exposure to high/low humidity cycles. The barrier layer of the multilayer coated paper reduced the dimensional changes and surface roughness increase caused by humidity and helped maintain the conductivity of printed tracks. As proof of concept functional devices, hygroscopic insulator field effect transistors were printed on the multi- layer curtain coated paper using a custom-built roll-to-roll hybrid printer.
Cambridgepp 995-1006Elastic Properties of Sheet and Materials from Vibration TestingAbstractPDF
Many materials, including paper products, come in sheet form and exhibit orthotropic symmetry. Information about the elastic stiffnesses of such materials can often be obtained quickly and accurately using a measurement method based on the vibration modes and natural frequencies of rectangular panels. The method is outlined and illustrated, and some case studies discussed in which the method is applied to fibre-reinforced composite materials and to the selection of wood for musical instruments.