Engineering fine paper by utilising the structural elements of the raw materials

The objective of this thesis was to explore the possible ways of using the intrinsic properties of cellulosic pulp fibres and inorganic pigments, by combining these elements using non-standard procedures, as a means to engineer a new composite material – a novel uncoated woodfree paper with improved physical properties. Precipitated calcium carbonate (PCC) was used as the inorganic pigment in this study. To accomplish this objective, we conducted a preliminary study on web addition followed by detailed studies on in-situ precipitation in fibrillated pulp suspensions and blending of novel furnish materials. We evaluated the different technological approaches by analysing the production process and product quality. In the first approach, chemical precipitation and spraying of filler dispersion onto a fibrous web, and mechanically pressing to assist penetration into the network, were compared against conventional filler dosage before web forming. The results showed that web addition approach results in higher tensile strength and lower light scattering of paper. Filler agglomeration and optical crowding, in chemical precipitation and web application respectively, resulted in significantly deteriorating the light scattering of the handsheets. The experimental conditions were not sufficient to obtain an even distribution of filler along the thickness direction of paper and the filler characteristics were not optimised in this study. In the second technique, precipitation onto fibrillated pulp suspensions was investigated by varying the pulp substrate, PCC crystal structure, and pre-refining a mixture of pulp and milk of lime. According to the research findings, PCCs formed by precipitation of calcium carbonate onto cellulosic fibrils and fibres do not necessarily have the same characteristics as reference PCCs formed by carbonizing milk of lime. Precipitation of calcium carbonate onto fibrillated fibres and microfines increases the retention of filler but impairs the dewatering of handsheets during pressing. Higher amount of fibrillated cellulosic substrates in combination with appropriate filler morphology, scalenohedral or rhombohedral, contribute to increased bond strength and light scattering of traditional fine paper. Pre-refining a mixture of pulp and calcium hydroxide results in grinding of lime, and hence, the composites have a greater surface area than the reference filler. Composite filled handsheets, from this study, exhibited high light scattering. In the third method, the microfines-filler composite was envisioned as the backbone structure for a new composite material – uncoated fine paper. In the new composite paper, strength properties arise from the microfibrillated cellulose, bulk and pores originate from the filler surrounded by fibrils, whereas tear strength is imparted by a minimal proportion of pulp fibres in the composite. Compared to conventional fibre based fine paper, even at high filler loading the new composite material showed higher bending stiffness, tensile and tear indices, internal bond strength, light scattering and brightness properties. The new concept of fines-pigment-based furnish enables us to load pigments in uncoated wood free paper up to 50%-60%. However, dewatering time is considerably longer. This method needs to be optimised, with further research on dewatering, and printability, before scaling it to an industrial process. This study shows the potential of different approaches, novel furnish components and addition of pigment onto a formed web, in the creation of new composite fine paper. Novel composite structure for fine paper can be achieved by employing the smallest component of pulp fibres, cellulosic microfines, in combination with pigments. The characteristics of microfines and crystal structure of pigments are important control variables in the formation and properties of the new composite paper. On the other hand, cellulosic microfines are highly swollen and retard dewatering. Therefore, further optimisation of process methodology and product quality can be expected to lead to some useful advances in commercialisation of this technology

STRUCTURE AND PROPERTIES OF SOME NATURAL CELLULOSIC FIBRILS

This study examines the properties of cellulosic fibrillar fines manufactured from different pulp raw materials, bleached softwood kraft (bswk), themomechanical (TMP), and non-wood sisal. Chemical characterisation showed that the carbohydrate and lignin contents of sisal were between those of bswk and TMP. Sisal was found to contain about three times more calcium than bswk and TMP. Measurements from the immobilization kinetics showed that the solids content after immobilization was highest for the sisal suspension followed by TMP and bswk. This indicates that the dewatering ability of the fines suspension increases in the order bswk<TMP<sisal. The loss modulus (G'') was maxmium with bswk, indicating that the greatest viscous dissipation before immobilisation took place in the bswk suspension. The strength properties of fines sheets decreased in the order bswk>TMP>sisal. This is due to the highly fibrillated nature of bswk fines, as illustrated by fibre saturation point (FSP), differential scanning calorimetric (DSC), and hydrodynamic specific volume (HSV) measurements

HIV transmission risk through anal intercourse: systematic review, meta-analysis and implications for HIV prevention

Background The human immunodeficiency virus (HIV) infectiousness of anal intercourse (AI) has not been systematically reviewed, despite its role driving HIV epidemics among men who have sex with men (MSM) and its potential contribution to heterosexual spread. We assessed the per-act and per-partner HIV transmission risk from AI exposure for heterosexuals and MSM and its implications for HIV prevention

Plasmodium Food Vacuole Plasmepsins Are Activated by Falcipains*

Intraerythrocytic malaria parasites use host hemoglobin as a major nutrient source. Aspartic proteases (plasmepsins) and cysteine proteases (falcipains) function in the early steps of the hemoglobin degradation pathway. There is extensive functional redundancy within and between these protease families. Plasmepsins are synthesized as integral membrane proenzymes that are activated by cleavage from the membrane. This cleavage is mediated by a maturase activity whose identity has been elusive. We have used a combination of cell biology, chemical biology, and enzymology approaches to analyze this processing event. These studies reveal that plasmepsin processing occurs primarily via the falcipains; however, if falcipain activity is blocked, autoprocessing can take place, serving as an alternate activation system. These results establish a further level of redundancy between the protease families involved in Plasmodium hemoglobin degradation

Clients of sex workers in Switzerland: it makes sense to counsel and propose rapid test for HIV on the street, a preliminary report.

BACKGROUND: Clients of street sex workers may be at higher risk for HIV infection than the general population. Furthermore, there is a lack of knowledge regarding HIV testing of clients of sex workers in developed countries. METHOD: This pilot study assessed the feasibility and acceptance of rapid HIV testing by the clients of street-based sex workers in Lausanne, Switzerland. For 5 evenings, clients in cars were stopped by trained field staff for face-to-face interviews focusing on sex-related HIV risk behaviors and HIV testing history. The clients were then offered a free anonymous rapid HIV test in a bus parked nearby. Rapid HIV testing and counselling were performed by experienced nurse practitioners. Clients with reactive tests were offered confirmatory testing, medical evaluation, and care in our HIV clinic. RESULT: We intercepted 144 men, 112 (77.8%) agreed to be interviewed. Among them, 50 (46.6%) had never been tested for HIV. A total of 31 (27.7%) rapid HIV tests were performed, 16 (51.6%) in clients who had not previously been tested. None were reactive. Initially, 19 (16.9%) additional clients agreed to HIV testing but later declined due to the 40-minute queue for testing. CONCLUSION: This pilot study showed that rapid HIV testing in the red light district of Lausanne was feasible, and that the clients of sex workers accepted testing at an unexpectedly high rate. This setting seems particularly appropriate for targeted HIV screening, since more than 40% of the clients had not previously been tested for HIV even though they engaged in sex-related HIV risk behaviour

Antimalarial activity of azadipeptide nitriles

Azadipeptide nitriles-novel cysteine protease inhibitors-display structure-dependent antimalarial activity against both chloroquine-sensitive and chloroquine-resistant lines of cultured Plasmodium falciparum malaria parasites. Inhibition of parasite's hemoglobin-degrading cysteine proteases was also investigated, revealing the azadipeptide nitriles as potent inhibitors of falcipain-2 and -3. A correlation between the cysteine protease-inhibiting activity and the antimalarial potential of the compounds was observed. These first generation azadipeptide nitriles represent a promising new class of compounds for antimalarial drug development