47 research outputs found
The role of sodium silicate in newsprint deinking.
Thesis (M.Sc.)-University of Natal, Durban, 2003.Mondi Ltd. operates a deinking plant at its Merebank mill. The plant recycles 85 000
tons per annum of flat news and magazine to produce a furnish for its newsprint
papermachines. A review of the relevant pulping and flotation chemistry literature
revealed that the role played by sodium silicate appears to be multi-faceted and in
some dispute. Sodium silicate has an undisputed role in pH buffering, hydrogen
peroxide stabilisation and the prevention of fibre yellowing. However, its role in
deinking is said to be that of an ink collector or alternatively an ink dispersant. The
mill's own experience has shown that the sodium silicate plays a vital role in the
deinking process.
Sodium silicate's ability to disperse ink, both alone and in the presence of calcium ions
and fatty acid soaps, was investigated using a model ink system. A representative
newsprint ink base was dispersed in the laboratory under conditions similar to those
encountered in a deinking pulper. The resultant dispersions were studied using
turbidity and particle size analysis. The morphology of the ink particles was determined
using a scanning electron microscope. Sodium silicate proved to be a poor disperser of
ink particles, but nevertheless appeared to greatly influence the dispersing properties
of the soap in the presence of calcium ions.
The nature of the interactions between sodium silicate, calcium ions and the collector
soap were studied in an attempt to elucidate the role of sodium silicate. A model
system consisting of the sodium salt of collector soap, calcium ions and sodium silicate
was studied under the conditions that prevail in a typical newsprint deinking pulper. It
was found that the soap and the sodium silicate compete for the calcium ions, and
sodium silicate showed a measurable chelating e:ffect on calcium ions. Thus,
increasing levels of sodium silicate lead to an increase in the concentration of sodium
soap in solution. It was hypothesised that this effect would lead to better dispersion of
ink particles and improved deinking performance.
This chelating effect was evaluated in laboratory deinking studies. Samples of
newsprint were pulped in a 251 Lamort laboratory pulper under a variety of conditions,
viz. with fresh water, with an excess of soap, with an excess of calcium, with and
without sodium silicate. The pulps were floated in a 201 flotation cell. The brightness and colour of the unfloated and floated pulps were measured. The level of the final
brightness after flotation was taken as a measure of deinking efficiency.
The highest final brightness was achieved when there was an excess of sodium soap
and a low Ca hardness in the pulper. Softening the water used in pulping without
adding excess sodium soap did not significantly improve pulp brightness. The lowest
final brightness occurred in the presence of an excess of calcium in the pulper. Calcium
in the pulper in the presence of sodium silicate did not result in a significantly lower
final brightness.
The results support the hypothesis that sodium silicate sequesters the soluble calcium
in a pulping system, thereby increasing the sodium soap concentration and the
resultant deinking performance. Apart from sodium silicate's chief role as a peroxide
stabiliser, the sequestering action on calcium appears to be its main mechanism of
action in a deinking system.
An appreciation of this role will facilitate the optimisation of deinking systems with
respect to calcium hardness and silicate concentration. To this end it was
recommended that the Merebank deinking plant should evaluate the use of water with
a low calcium ion concentration and the addition of some soap into the pulper to
improve their deinking plant performance
Neural network modelling and prediction of the flotation deinking behaviour of complex recycled paper mixes.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2011.In the absence of any significant legislation, paper recycling in South Africa has grown
to a respectable recovery rate of 43% in 2008, driven mainly by the major paper
manufacturers. Recently introduced legislation will further boost the recovery rate of
recycled paper. Domestic household waste represents the major remaining source of
recycled paper. This source will introduce greater variability into the paper streams
entering the recycling mills, which will result in greater process variability and operating
difficulties. This process variability manifests itself as lower average brightness or
increased bleaching costs. Deinking plants will require new techniques to adapt to the
increasingly uncertain composition of incoming recycled paper streams. As a
developing country, South Africa is still showing growth in the publication paper and
hygiene paper markets, for which recycled fibre is an important source of raw material.
General deinking conditions pertaining to the South African tissue and newsprint
deinking industry were obtained through field surveys of the local industry and
assessment of the current and future requirements for deinking of differing quality
materials.
A large number of operating parameters ranging from waste mixes, process variables
and process chemical additions, typically affect the recycled paper deinking process.
In this study, typical newsprint and fine paper deinking processes were investigated
using the techniques of experimental design to determine the relative effects of
process chemical additions, pH, pulping and flotation times, pulping and flotation
consistencies and pulping and flotation temperatures on the final deinked pulp
properties.
Samples of recycled newsprint, magazines and fine papers were pulped and deinked
by flotation in the laboratory. Handsheets were formed and the brightness, residual ink
concentration and the yield were measured. It was determined that the type of
recycled paper had the greatest influence on final brightness, followed by bleaching
conditions, flotation cell residence time and flotation consistency. The residual ink
concentration and yield were largely determined by residence time and consistency in
the flotation cell.
The laboratory data generated was used to train artificial neural networks which
described the laboratory data as a multi-dimensional mathematical model. It was found
that regressions of approximately 0.95, 0.84 and 0.72 were obtained for brightness,
residual ink concentration and yield respectively.
Actual process data from three different deinking plants manufacturing seven different
grades of recycled pulp was gathered. The data was aligned to the laboratory
conditions to take into account the different process layouts and efficiencies and to
compensate for the differences between laboratory and plant performance. This data
was used to validate the neural networks and select the models which best described
the overall deinking performances across all of the plants. It was found that the
brightness and residual ink concentration could be predicted in a commercial operation
with correlations in excess of 0.9. Lower correlations of ca. 0.5 were obtained for yield.
It is intended to use the data and models to develop a predictive model to facilitate the
management and optimization of a commercial flotation deinking processes with
respect to waste input and process conditions
Effect of interchain coupling on conducting polymer luminescence: excimers in derivatives of poly(phenylene vinylene)
Optical excitation of a chain in a polymer film may result in formation of an
excimer, a superposition of on-chain excitons and charge-transfer excitons on
the originally excited chain and a neighboring chain. The excimer emission is
red-shifted compared to that of an on-chain exciton by an amount depending on
the interchain coupling . Setting up the excimer wavefunction and
calculating the red shift, we determine average values, referred to a
monomer, of 0.52 eV and 0.16 eV for poly(2,5-hexyloxy -phenylene
cyanovinylene), CN-PPV, and poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-1, 4
p-phenylene vinylene], MEH-PPV, respectively, and use them to determine the
effect of interchain distance on the emission.Comment: 10 pages, RevTeX, 1 PS figure, replaced version of cond-mat/9707095,
accepted for publication in Phys. Rev. B, Rapid Communicatio
Excited States of Ladder-type Poly-p-phenylene Oligomers
Ground state properties and excited states of ladder-type paraphenylene
oligomers are calculated applying semiempirical methods for up to eleven
phenylene rings. The results are in qualitative agreement with experimental
data. A new scheme to interpret the excited states is developed which reveals
the excitonic nature of the excited states. The electron-hole pair of the
S1-state has a mean distance of approximately 4 Angstroem.Comment: 24 pages, 21 figure
Single-cell RNA sequencing uncovers the nuclear decoy lincRNA PIRAT as a regulator of systemic monocyte immunity during COVID-19
The systemic immune response to viral infection is shaped by master transcription fac-tors, such as NF-ÎșB, STAT1, or PU.1. Although long noncoding RNAs (lncRNAs)have been suggested as important regulators of transcription factor activity, their contri-butions to the systemic immunopathologies observed during SARS-CoV-2 infectionhave remained unknown. Here, we employed a targeted single-cell RNA sequencingapproach to reveal lncRNAs differentially expressed in blood leukocytes during severeCOVID-19. Our results uncover the lncRNA PIRAT (PU.1-induced regulator of alar-min transcription) as a major PU.1 feedback-regulator in monocytes, governing the pro-duction of the alarmins S100A8/A9, key drivers of COVID-19 pathogenesis. Knockoutand transgene expression, combined with chromatin-occupancy profiling, characterizedPIRATasanucleardecoyRNA,keepingPU.1frombindingtoalarminpromotersandpromoting its binding to pseudogenes in naĂŻve monocytes. NF-ÎșBâdependent PIRATdown-regulation during COVID-19 consequently releases a transcriptional brake, fuelingalarmin production. Alarmin expression is additionally enhanced by the up-regulation ofthe lncRNA LUCAT1, which promotes NF-ÎșBâdependentgeneexpressionattheexpenseof targets of the JAK-STAT pathway. Our results suggest a major role of nuclear noncod-ing RNA networks in systemic antiviral responses to SARS-CoV-2 in humans
âGod is Hidden in the Earthly Kingdom:â The Lutheran Two-Kingdoms Theory as Foundation of Scandavanian Secularity
Martin Lutherâs signature âtwo kingdomsâ teaching of the sixteenth century was an early and innovative theory of secularization that lies at the heart of historical Scandinavian culture. Defying the organic medieval models of Western Christendom, Luther separated the heavenly and earthly kingdoms, the saint and the sinner, faith and reason, church and the state, Gospel and the Law, as well as the spiritual and secular uses of law, government and authority. Though God is separated from day-to-day life, Luther wrote, God is still hidden in the earthly kingdomâ and can be seen through various âmasks,â âmists,â and âmimes.â Though the visible church is separated from the state and other institutions, religion remains pervasive in the common callings of every person to be Godâs prophet, priest and king in every vocation and location of life. Lutherâs two kingdoms theory is a complicated and controversial part of this thinking, but it is worth re-exploring today as pluralistic Scandinavia faces strong new pressures of both sacralization and secularization and seeks to discern anew âthe hidden sacraliity of the secular.