| 1. |
- Andersson, Martin, 1979-
(författare)
-
Asthma in school age : prevalence, incidence and remission in relation to environmental determinants
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background In the past half-century, the prevalence of asthma among children and adolescents has risen and asthma has become an important public health challenge in Sweden as well as in many other countries, necessitating further studies on this complex disease and its risk factor pattern. The studies included in this thesis aimed to investigate the clinical expression of childhood asthma over time, to describe the determinants of new-onset and remission of asthma, and to evaluate possible environmental risk factors in northern Sweden.Methods As the result of a repeated questionnaire survey among primary school children aged 7-8 years in three municipalities in the north of Sweden, two pediatric cohorts were formed, one in 1996 (n=3430) and one in 2006 (n=2585). The cohort created in 1996 was followed annually until the age of 19 years. Skin prick testing was performed on children in both cohorts. Lung function and bronchial hyperreactivity testing were carried out in children with asthma in the first cohort. The study participation and retention rates were very high in both cohorts. Among children in the second cohort living in Luleå, the home addresses were assigned to coordinates in a geographical information system (GIS) to evaluate the impact on respiratory health of living near roads with much traffic, which was measured as the number of vehicles daily. We used a validated reported diagnosis of asthma and International Study of Asthma and Allergies in Childhood (ISAAC) questions were incorporated into the questionnaire. A cross-sectional study of children of the same age ten years apart, longitudinal studies on asthma incidence and remission as well as a cross-sectional study on vehicle traffic were performed.Results While children aged 7-8 years in 2006 more often had a physician-diagnosed asthma compared to children of the same age in 1996 (7.4% vs 5.7%, p<0.001), they had less asthma symptoms, especially severe symptoms. In parallel, a more beneficial environment and a more intense treatment with inhaled corticosteroids (ICS) were observed. The explanation for this change in clinical expression probably includes also an increased awareness and diagnosing of asthma. From age 12 years to age 19 years, the cumulative incidence of physician-diagnosed asthma was 7.2% and of current wheeze 22.0%. The risk of new-onset asthma in adolescence was increased among girls, sensitized and those with heredity for asthma. Smoking and home dampness increased the risk for incident wheeze. The risk for both incident asthma and wheeze was inversely related to number of siblings. Among children with current asthma at age 7-8 years, 21% were in remission, 38% had periodic asthma and 41% had persistent asthma at a follow-up at age 19 years. Subjects in remission and with periodic asthma had significantly less airway obstruction and showed less bronchial hyperreactivity compared to subjects with persistent asthma. The probability of asthma remission from childhood to early adulthood was significantly increased by absence of allergic sensitization, male gender and a low asthma severity scoring at age 7-8 years. Sensitization to furred animals was more important as a determinant of both incidence and remission than sensitization to pollen. Living close to roads with high traffic flows, especially with heavy vehicles, was associated with an increased risk for current wheeze. Stratified analyses showed that the effect of traffic on asthma and wheeze was restricted to non-sensitized subjects.Conclusion Asthma onset in adolescence was more common among girls and remission was more common among boys. Children sensitized to furred animals and children with a more severe asthma were risk groups for persistence of asthma. Environmental factors such as smoking and dampness were associated to onset of asthma symptoms during adolescence, and vehicle traffic was associated with asthma symptoms among children also in a small city with relatively low traffic flows. Preventive measures like smoking reduction programs, improvement of damp housing conditions and separation of areas where many children live from heavily trafficked roads could prove to be beneficial.
|
|
| 2. |
- Carlsen, Hanne Krage, 1981-
(författare)
-
Health effects of air pollution in Iceland : respiratory health in volcanic environments
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Air pollution has adverse effects on human health. The respiratory system is the most exposed and short-term changes in air pollution levels have been associated with worsening of asthma symptoms and increased rates of heart attacks and stroke. Air pollution in cities due to traffic is the major concern, as many people are exposed. However, natural sources of air pollution such as natural dust storms and ash from volcanic eruptions can also compromise human health. Exposure to volcanic eruptions and other natural hazards can also threaten mental health. Air pollution has not been extensively studied in Iceland, in spite of the presence of several natural pollution sources and a sizeable car fleet in the capital area.The aim of this thesis was to determine if there was a measurable effect on health which could be attributed to air pollution in Iceland. This aim was pursued along two paths; time series studies using register data aimed to determine the short-term association between daily variation in air pollution and on one hand daily dispensing of anti-asthma medication or the daily number of emergency room visits and emergency admissions for cardiopulmonary causes and stroke. The other method was to investigate if exposure to the Eyjafjallajökull volcanic eruption was associated with adverse health outcomes, either at the end of the eruption, or 6 months later.In paper I time series regression was used to investigate the association between the daily number of individuals who were dispensed anti-asthma medication and levels of the air pollutants particle matter with an aerodynamic diameter less than 10 μm (PM10), nitrogen dioxide (NO2), ozone (O3), and hydrogen sulfide (H2S) during the preceding days. For the study period 2006-9, there were significant associations between the daily mean of PM10 and H2S and the sales of anti-asthma medication 3 to 5 days later. Giving the exposure as the highest daily one-hour mean gave more significant results. Air pollution negatively affected the respiratory health of asthma medication users, prompting them to refill their prescriptions before they had originally intended to.In paper II the main outcome was the number of individuals seeking help at Landspitali University Hospital emergency room for cardiopulmonary disease or stroke. Time series regression was used to identify the lag that gave the best predictive power, and models were run for data for 2003-9 pollutants PM10, NO2, and O3. O3 was significantly associated with the number of emergency hospital visits the same day and two days later in all models, and both for men, women and the elderly. Only emergency hospital visits of the elderly were associated with NO2, and there were no associations with PM10.In paper III the aim was to investigate if the health effects of PM10 were affected by the addition of volcanic ash from the 2010 eruption of Eyjafjallajökull and 2011 eruption of Grímsvötn to PM10 in the capital area. Time series regression of emergency hospital visits and PM10 before and after the Eyjafjallajökull eruption showed that the effect tended to be higher after the eruption, but the results were not significant. Analysis with a binary indicator for high levels of PM10 from volcanic ash and other sources showed that volcanic ash was associated with increased emergency hospital visits. There were no associations with high levels of PM10 from other sources.In paper IV, the health of the population exposed to the ongoing eruption of Eyjafjallajökull in 2010 was investigated thoroughly. Lung function in adults was better than in a reference group from the capital area, though many reported sensory organ irritation symptoms and symptoms of stress and mental unhealth, especially those with underlying diseases.Paper V report the results from a questionnaire study which was carried out six months after the Eyjafjallajökull eruption. The study population comprised a cohort of south Icelanders exposed to the eruption to varying degrees and a reference group from north Iceland. Respiratory and eye symptoms were much more common in south Icelanders than in the reference group, after adjusting for demographic characteristics. Mental unhealth rates had declined considerably.In the studies, we found that urban air pollution and natural particles have short-term effects on anti-asthma medication dispensing and emergency room visits and hospital admissions. Exposure to natural particles in the form of volcanic dust was associated with increased respiratory symptoms in a very exposed population. There were indications that volcanic ash particles were associated with increased emergency hospital visits in the following days.
|
|
| 3. |
|
|
| 4. |
- Hedman, Linnea, 1979-
(författare)
-
Epidemiological studies of asthma and allergic diseases in teenagers : methodological aspects and tobacco use
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Parental reports are often used in studies of asthma and allergic diseases in children. A change in respondent from parent to index subject usually occurs during adolescence. Little is known about the effects this change in method might have on the outcomes of a longitudinal study. Smoking is a major cause of respiratory symptoms among adults and environmental tobacco smoke (ETS) is a risk factor for asthma among children. Less is known about these associations among teenagers. In order to improve prevention of smoking, it is important to identify populations at risk of becoming smokers. The aim of this thesis were to 1) evaluate the methodological change from parental to self-completion of a questionnaire about asthma and allergic diseases, and 2) to study determinants for, and respiratory health effects of ETS and personal smoking in teenagers.In 1996, a longitudinal study of asthma and allergic diseases among schoolchildren started within the Obstructive Lung Disease in Northern Sweden (OLIN) studies. All children in first and second grades (aged 7-8 years) in three municipalities, Luleå, Kiruna and Piteå (n=3,525) were invited and 97% participated by parental completion of a questionnaire. The cohort has been followed with annual questionnaires until age 16-17 years and with high participation rates (>91%). From age 12-13 years, the teenagers were the respondents and questions about their tobacco use were included. In addition to the questionnaire completed by the teenagers at age 13-14 years, a questionnaire was also distributed to a random sample of 10% of the parents and 294 participated (84%). The parents and the teenagers reported a similar prevalence of asthma, respiratory symptoms, rhinitis, eczema and environmental factors. Two statistically significant differences were found: the teenagers reported a higher prevalence of wheezing during or after exercise (14% vs 8%, p<0.05), and having a dog in the home in the last 12 months (42% vs 29%, p<0.001). Answer agreement between parents and teenagers on questions about asthma was almost perfect with kappa values of 0.8-0.9. Corresponding kappa values for questions about respiratory symptoms and rhinitis were 0.3-0.6 and for eczema 0.5-0.6. Agreement about environmental factors varied from 0.2-0.9. Kappa values for parental smoking were 0.8-0.9. The risk factor pattern for allergic diseases was similar regardless of respondent, ie parent or teenager.The prevalence of smoking increased from 3% at 12-13 years to 6% at 14-15 years. Smoking was more common among girls, while the use of snus was more common among boys. Significant risk factors related to smoking among teenagers were smoking family members, female sex and living in an apartment. Having physician-diagnosed asthma did not prevent the teenagers from becoming smokers. Factors related to using snus were a smoking mother and male sex. Daily smokers aged 16-17 years (9%) reported a significantly higher prevalence of wheezing and physician-diagnosed asthma compared to non-smokers. There was a significant dose-response association with higher prevalence of wheeze among those who smoked ≥11 cigarettes per day compared to those who smoked ≤10 per day. In multivariate analyses, maternal environmental tobacco smoke exposure was a significant risk factor for ever wheeze and physician-diagnosed asthma at age 16-17 years, while daily smoking was a risk factor for current wheeze.In conclusion, the methodological change of questionnaire respondent from parent to index subject did not substantially alter the findings of this longitudinal study. There were significant sex differences in the tobacco use: smoking was more common among girls and snus was more common among boys. The most important factor related to tobacco use was presence of family members who smoke. Both maternal ETS exposure and personal smoking was associated with asthma and wheeze in adolescence. ETS was associated with lifetime symptoms but daily smoking was more strongly associated with current symptoms.
|
|
| 5. |
- Modig, Lars, 1976-
(författare)
-
Asthma, rhinitis, and asthma-related symptoms in relation to vehicle exhaust using different exposure metrics
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Air pollution is a well known public health problem that involves both long-term and acute effects. An outcome associated with traffic-related air pollution is respiratory illness. Many studies have described the relationship between asthmatic symptoms and traffic-related air pollution; however, few have investigated the potential of air pollution to cause asthma itself, especially among adults. The overall aim of this thesis was to study the relationship between vehicle exhaust levels at home and the prevalence of self-reported annoyance and asthmatic symptoms, and the incidence of asthma and rhinitis. These relationships were evaluated using different indicators of exposure with a high spatial resolution. Three different data sets were used for the four papers included in this thesis. The first paper (paper I) is based on a questionnaire that was sent to a random selection of the adult population within three Swedish cities (Gothenburg, Uppsala, and Umeå) as part of the Swedish Environmental Protection Agency’s health-related environmental monitoring. The aim was to study the degree of self-reported annoyance and the prevalence of asthmatic symptoms in relation to the levels of vehicle exhaust outside the home. The level of exposure was described using modeled levels of nitrogen dioxide (NO2) as the exposure indicator. The second paper (paper II) is based on new asthma cases identified within the Obstructive Lung disease In Northern Sweden (OLIN) study, each with a matched referent. The aim of this study was to analyze if new cases of asthma had higher levels of vehicle exhaust outside the home compared to the population controls. Exposure was assessed using both measured levels of NO2 outside each home, and by summarizing the amount of traffic within a 200 metre buffer surrounding each participant’s home. Papers III and IV were based on the Respiratory Health in Northern Europe (RHINE) Cohort, a prospective cohort of adults included in 1990 and followed up with in 1999. The proportion of new cases of asthma (papers III and IV) and rhinitis (paper IV) were identified based on the answers from the initial and follow-up questionnaires. In paper III, exposure was assessed by using meteorological dispersion models to calculate the levels of NO2 outside each home as an indicator of the levels of vehicle exhaust. As an alternative indicator, the distance from each participant’s home to the nearest major road was calculated using geographical information system (GIS) tools. The exposure assessment in paper IV was also based on meteorological dispersion models, but expressed the levels of vehicle exhaust as particle mass concentration. The results show that the levels of vehicle exhaust outside the home are significantly correlated with the degree of self-reported annoyance and the prevalence of asthmatic symptoms, and also with the risk of developing asthma, but not rhinitis, among adults. The odds ratio (OR) for high annoyance to vehicle exhaust and reporting asthmatic symptoms was 1.14 (95% Confidence Interval, CI 1.11-1.18) and 1.04 (95% CI 1.01-1.07) per 1 µg/m3 increase in the NO2 level outside the home, respectively. Paper II showed there was a non-significant tendency for increased risk of developing asthma among those living with high levels of vehicle exhaust outside their home. This finding was then supported by papers III and IV, showing a significant relationship between the onset of asthma and the mean (winter) levels of NO2 outside the home (OR=1.46, 95% CI 1.07-1.99 per 10 µg/m3) and the levels of vehicle exhaust particles outside the home. In paper III, living close to a major road was significantly related to the risk of developing asthma. No significant results were shown between vehicle exhaust and rhinitis. In conclusion, vehicle exhaust outside the home is associated with the prevalence of annoyance and asthmatic symptoms, and with the risk of developing asthma, but not rhinitis, among adults.
|
|
| 6. |
- Olsson, David, 1982-
(författare)
-
Adverse effects of exposure to air pollutants during fetal development and early life : with focus on pre-eclampsia, preterm delivery, and childhood asthma
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background Air pollution exposure has been shown to have adverse effects on several health outcomes, and numerous studies have reported associations with cardiovascular morbidity, respiratory disease, and mortality. Over the last decade, an increasing number of studies have investigated possible associations with pregnancy outcomes, including preterm delivery. High levels of vehicle exhaust in residential neighborhoods have been associated with respiratory effects, including childhood asthma, and preterm birth is also associated with childhood asthma.The first aim of this thesis was to investigate possible associations between air pollution exposure and pregnancy outcomes – primarily preterm delivery but also small for gestational age (SGA) and pre-eclampsia – in a large Swedish population (Papers I–III). The second aim was to study any association between exposure to high levels of vehicle exhaust during pregnancy and infancy and prescribed asthma medication in childhood (Paper IV).Methods The study cohorts were constructed by matching other individual data to the Swedish Medical Birth Register. In the first two studies, air pollution data from monitoring stations were used, and in the third and fourth studies traffic intensity and dispersion model data were used.Preterm delivery was defined as giving birth before 37 weeks of gestation. SGA was defined as having a birth weight below the 10th percentile for a given duration of gestation. Pre-eclampsia was defined as having any of the ICD-10 diagnosis codes O11 (pre-existing hypertension with pre-eclampsia), O13 (gestational hypertension without significant proteinuria), O14 (gestational hypertension with significant proteinuria), or O15 (eclampsia). Childhood asthma medication was defined as having been prescribed asthma medication between the ages of five and six years.Results We observed an association between ozone exposure during the first trimester and preterm delivery. First trimester ozone exposure was also associated with pre-eclampsia. The modeled concentration of nitrogen oxides at the home address was associated with pre-eclampsia, but critical time windows were not possible to investigate due to high correlations between time windows. We did not observe any association between air pollution exposure and SGA. High levels of vehicle exhaust at the home address, estimated by nitrogen oxides and traffic intensity, were associated with a lower risk of asthma medication.Conclusion Air pollution exposure during pregnancy was associated with preterm delivery and pre-eclampsia. We did not observe any association between air pollution levels and intrauterine growth measured as SGA. No harmful effect of air pollution exposure during pregnancy or infancy on the risk of being prescribed asthma medication between five and six years of age was observed.
|
|
| 7. |
- Olstrup, Henrik, 1978-
(författare)
-
Air pollution and health – Indicators, trends and impacts
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on some of the limitations and difficulties that exist when it comes to quantifying the human health effects that arise as a result of air pollution exposure. The following four issues are particularly analysed and discussed: 1) The measurement techniques used for carbonaceous particles and their lack of consistency; 2) Do the health risks associated with exposure to PM10 depend on the content of elemental carbon in the aerosol?; 3) Trends in air pollutants and the health effects that arise as a result of changed exposure to the measured pollutants; 4) The associations between the measured concentrations of different air pollutants in Stockholm and the daily number deaths; 5) Air quality indicators and health outcomes as basis for an air quality health index (AQHI).The method that has been used is largely based on empirical data analysis, where further statistical processing has been used in order to clarify the scientific issues. The overall conclusions are the following: 1) The health impact assessments associated with exposure to carbonaceous particles would benefit from the introduction of a more uniform measurement technique in order to get more consistent and reliable results; 2) The health risks associated with exposure to PM10 are dependent on the content of elemental carbon; 3) The life expectancy increase associated with decreasing NOx trends during 1990–2015 in Stockholm, Gothenburg and Malmo make up as much as about 20 % of the total gain in life expectancy during this period, which clearly shows the beneficial effects related to decreased exposure; 4) The associations between daily mortality and the concentrations of O3 and PM2.5-10 in Stockholm are statistically significant, which does not apply to the exhaust-related pollutants, possibly reflecting behavioural factors affecting the degree of exposure; 5) In comparison with the currently used air quality index (AQI), the air quality health index (AQHI) is a more useful tool in order to address the short-term health effects associated with multi-pollutant exposure to NOx, O3, PM10 and birch pollen.We hope that these findings will be useful from a policy point of view. Introducing a more consistent measurement technique for soot particles would be beneficial in assessing the health effects related to exposure to these particles. The increase in life expectancy associated with decreasing NOx trends shows the benefits from a public health perspective when it comes to introducing emission-reducing measures from traffic. The AQHI would be beneficial to implement in legislation, as it is based on several pollutants, which means that the cumulative health effects associated exposure to several different air pollutants are accounted for.
|
|
| 8. |
- Orru, Hans, 1980-
(författare)
-
Exposure to particulate matter and the related health impacts in major Estonian cities
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Particulate matter (PM) is one of the most studied and problematic pollutants due to its toxicity and relatively high concentrations. This thesis aims to clarify the main sources and exposures of PM in Tallinn and Tartu, study the associations with health effects, and estimate the extent of those effects with health impact assessment (HIA).It appeared that the main sources of particulate air pollution in Tallinn (the capital of Estonia) and Tartu (the second largest city of Estonia) are local heating and traffic, including road dust. In addition to local emissions, particulate levels are affected by transboundary pollution. If the transboundary air masses originated from the Eastern European areas, the concentration as well as the oxidative capacity of fine particles was significantly higher in urban background air in Tartu compared to air masses coming from Scandinavian areas (Paper I).During the last 15 years, traffic increase has been very fast in Tartu. However, due to the improvement in vehicle technology during this period, there has been only a slight increase in concentration of exhaust particles (Paper II). Nevertheless, a greater increase in road dust emissions was detected.A statistically significant relationship between long-term exposure to those traffic induced particles and cardiac disease in the RHINE (Respiratory Health in Northern Europe) Tartu cohort was shown (Paper III). However, no significant associations with respiratory health were found.The HIA in Tallinn demonstrated 296 (95% CI = 76–528) premature deaths annually, because of PM (Paper IV). The average decrease in life expectancy was predicted to be 0.64 (95% CI 0.17–1.10) years. However, among risk groups it can be higher. In addition, several cardiovascular hospitalizations are related. The costs to society because of health effects reach up to €150 million annually (95% CI = 40–260) from premature deaths and hospitalization constitute an additional €0.3 million (95% CI = 0.2–0.4).The special HIA scenario, when more pollution fuel peat will be used in boiler houses was analysed as well (Paper V). It indicated that peat burning would result in up to 55.5 YLL per year within the population of Tartu. However, the health effects of pollution from current traffic, local heating, and industry are at least 28 times bigger.In conclusion, exposure to PM cause considerable health effects in the form of cardiopulmonary diseases in main Estonian cities.
|
|
| 9. |
- Raza, Wasif, 1971-
(författare)
-
Impacts of Active Transport on Health : with a focus on physical activity, air pollution, and cardiovascular disease
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: There are increasing number of health impact assessment studies investigating the health effects by transferring trips made by motorised transport to active commuting; however, air pollution exposure during active commuting and its impact on health has been less thoroughly assessed. It is furthermore uncertain whether there is any interaction effect between air pollution and physical activity for the risk of cardiovascular diseases. The overall aim of the thesis was to improve the knowledge base for assessments of the total impact on health of a mode shift resulting in both increased physical activity and increased air pollution exposure, especially regarding combined effects on cardiovascular risks.Methods: The thesis is based on four studies. In Study I, methodological issues related to the assessment of air pollution in previous studies on the health impact of changes in transport mode were critically reviewed. In Study II, the effect of leisure time and active commuting physical activity, on chronic diseases was quantified by conducting a random-effect meta-analysis. In two prospective cohort studies, participants of the Västerbotten Intervention Programme living in the Umeå region were studied to assess the impact as well as interaction effect of physical activity and air pollution on the incidence (Study III) and recurrence (Study IV) of cardiovascular diseases.Results: In previous studies on the health impact of changes in transport mode, there was a large methodological discrepancy between studies due to different assumptions for air pollution exposure assessments in general populations and commuters as well as methods for estimation of impacts. Randomeffect meta-analyses showed a beneficial effect of leisure time physical activity and active commuting on morbidity among individuals performing these activities at the minimum level of physical activity recommended by WHO, equivalent to 11.25 MET-hours per week. Beneficial effects of exercise on firstincident ischemic heart disease (IHD) were observed among individuals with high residential PM10/PM2.5 concentrations, but not among individuals with low concentrations. Adverse effects associated with high residential PM10 and PM2.5 concentrations were only observed among the individuals whom less frequently exercised. A statistically significant interaction effect was found between air pollution and exercise in training clothes for first-incident IHD but not for recurrence of IHD/stroke.Conclusions: The results in this thesis strengthen the public health message that physical activity is beneficial for cardiovascular health, even in areas with air pollution. Therefore, public health and transport policies should be designed to improve population health through promotion of active transport and mitigation of air pollution.
|
|
| 10. |
- Reyes Forsberg, Diana Carolina, 1984-
(författare)
-
Experimental study of alkalinisation of cellulose in industrial relevant conditions
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mercerisation of cellulose pulp with a solution of NaOH is the first step of manufacturing cellulose-based value-added products, e.g. viscose fibres and cellulose ethers. During this process, cellulose transforms into a swollen crystalline structure, alkali cellulose (Na-Cell). This increases the reactivity of the cellulose and makes it more accessible for reagents to penetrate and react with the hydroxyl groups. The mercerisation conditions are known to affect the degree of alkalinisation of cellulose as well as the final products. The main objective of this thesis is to investigate how the alkalinisation of softwood sulphite dissolving cellulose pulp is influenced by the co-variation of process variables in the mercerisation in industrial relevant conditions, for both viscose and cellulose ether production. This objective was achieved by quantitative analysis of the effect of simultaneous variation of a set of key parameters on the degree of alkalinisation (i.e. degree of activation, DoA) of the chosen dissolving pulp. Quantitative measurements were performed using Raman spectroscopy data, evaluated by partial least squares (PLS) regression. For mercerisation at viscose production conditions, the effect of studied variables on mass yield was also considered. In the case of mercerisation at ether processing conditions, formation of alkali cellulose at a fixed temperature was included. The knowledge obtained on mercerisation under ether processing conditions was then applied for preparation of the ionic cellulose ether carboxymethylcellulose (CMC). The overall results show that temperature has a strong effect on DoA and mass yield for mercerised samples under steeping conditions. Measured DoA decreases as the temperature increases from 20 to 70 °C. Mass yield correlates positively with the temperature up to 45-50 °C in the PLS model, after which the relation is negative. The [NaOH] and reaction time show a complex dependence of other variables. At mercerisation conditions for cellulose ether production, the NaOH/AGU stoichiometric ratio, denoted as (r), shows to be very important for DoA, with a positive correlation. At these mercerisation conditions, temperature shows no effect on DoA. The influence of the [NaOH] (which also refers to the concentration of water) shows a complex dependence on (r). As (r) increases and [NaOH] decreases, the measured DoA increases. Prolonged mercerisation time shows no significance in the modelled DoA. However, a gradual increase of the DoA over time was seen when mercerisation was performed with 30% and 40% [NaOH] at (r) = 0.8, suggesting a slow diffusion of NaOH and Na-Cell formation. 13C CP-MAS NMR measurements of samples produced at room temperature show that formation of the Na-Cell allomorph is mainly determined by the [NaOH]. However, in the transition area between Na-Cell I and Na-Cell II, (r) also seems to be of importance. An increase of DS in the produced CMC samples also shows to be consistent at such conditions with the increase in the measured DoA and with increased (r) and decreased [NaOH]. However, these conditions also favour the formation of by-products. In the synthesised CMC samples, a DS of up to 0.7 was achieved. Measured solubility was lower than expected for any given DS. This, along with the non-statistical distribution of monomer units in the polymer chains, indicates high heterogeneity in the synthesised samples. The distribution of substituents within the AGU shows attachment to hydroxyl oxygens in the order O3 < O2 ≈ O6. The relative importance of the substitution at O3 indicates an increase at this position when [NaOH] increases.The models presented in this thesis will hopefully serve as a basis for predicting the effects of the studied variables on the DoA, as well as on the mass yield of cellulose pulp when mercerisation conditions are adjusted. Moreover, it is believed that the presented studies can give a better understanding of mercerisation at cellulose ether conditions, hence enabling further development of this process step.
|
|
