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21.
  • Forsman, Samuel (författare)
  • Suggestions for innovation in the supplying of joinery products through the application of Lean-thinking and 3-D sensing
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The supplying of engineer-to-order joinery products to the construction industry is a novel research area in both the wood-related and the construction-related fields. The process of supplying the construction industry with highly refined one-of-a-kind wood products is here examined in order to explore possible process innovations to identify factors contributing to inefficiency, to define areas for innovation to improve industry performance, and to evaluate 3-D sensing technologies as a way of achieving a model-based joinery production. The organizations studied use a mixture of concept-to-order and design-to-order production strategies to produce what in this thesis are called engineer-to-order joinery products.The main consumer of the engineer-to-order joinery products are theconstruction industry, an industry that has been criticized for not keeping upwith other production industries in terms of quality, cost efficiency, innovation,and production methods. The development of Lean production principles andsupply chain management are innovations commonly suggested to increase the degree of industrialization in the construction industry, and this is reflected in the research approach adopted for the work described in this thesis. The conditions for supplying engineer-to-order joinery products to theconstruction industry have been studied and areas for innovation efforts aresuggested. The primary research question has been: Can new technology and new management methods be applied to improve process efficiency and efficacy in the supplying of engineer-to-order joinery products? Lean principles and 3-D sensing are two perspectives chosen to investigate this supply process. The study has used both qualitative and quantitative research methods, with a slight overweight towards the qualitative methods, as the context for the quantitative research has always been in focus. Real-world case studies have been used for the empirical data collection.The results suggest that there is a significant potential for increasing efficiency and efficacy through: greater focus on cross-organisational innovation focusing on higher levels of industrialisation, new forms of contractual relations, supply chain cooperation, improved knowledge-transfer and information management, developing competence on 3-D sensing and “BIM”-modelling, and through organisational consolidation.
22.
  • Gardelli, Viktor (författare)
  • To Describe, Transmit or Inquire Ethics and technology in school
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Ethics is of vital importance to the Swedish educational system, as in many other educational systems around the world. Yet, it is unclear how ethics should be dealt with in school, and prior research and evaluations have found serious problems regarding ethics in education. The field of moral education lacks clear and widely accepted definitions of key concepts, and these ambiguities negatively impact both research and educational practice. This thesis draws a distinction between three approaches to ethics in school – the descriptive ethics approach, the value transmission approach, and the inquiry ethics approach – and studies in what way (if at all) they are prescribed by the national curriculum for the Swedish compulsory school, how they relate to students’ moral reasoning about technology choices and online behaviour, and what pedagogical merits and disadvantages they have. Hopefully, this both contributes to reducing the ambiguities of the field, and to answering the question of how ethics should be dealt with in education.The descriptive ethics approach asserts that school should teach students empirical facts about ethics, such as what views and opinions people have. The value transmission approach holds that school should mediate some set of predefined values to the students and make sure the students come to accept these values. The inquiry ethics approach is the view that school should teach students to reason and think critically about ethics and to engage in ethical inquiry.The role of ethics in the curriculum has not been studied in light of the above distinction, in prior research, and such an investigation is undertaken here. The results suggest that ethics has a prominent, but complicated, role in the Swedish national curriculum. Although no explicit distinction is drawn or acknowledged in the curriculum, all three approaches are prescribed throughout the curriculum, albeit to different degrees. In the general section of the curriculum, the value transmission and inquiry ethics approaches are more extensively prescribed than the descriptive ethics approach. It was found that most of the syllabi contained explicit references to ethics, while some only contained implicit references to ethics, and two syllabi lacked references to ethics altogether. In the syllabi, the inquiry ethics approach is the most dominant, both in the sense of being present in the most syllabi, and in the sense of being more strongly prescribed in many of the syllabi where several approaches occur. The value transmission approach has the weakest role in the syllabi. In total, the inquiry ethics approach is the approach most strongly prescribed by the curriculum. But prior research has shown that inquiry ethics is very rarely implemented in the classroom. In this thesis, it is found that the inquiry ethics and the value transmission approaches are incompatible, given certain reasonable interpretations, which makes the finding that inquiry ethics is rarely implemented less surprising, since value transmission is practiced in schools.The students, in their moral reasoning about technology choices, reasoned in accordance with several classical normative theories – including consequentialism, deontological ethics and virtue ethics – and in doing so, they expressed reasoning that in the discussion is found to be in conflict with the values of the value foundation in the curriculum. These findings complement earlier findings, for example that students in their actions contradict the value foundation, by adding that such conflicts also exist in their reasoning. The existence of these conflicts is found to be problematic for a value transmission approach.Many of the students defended very restrictive views on disclosing personal information online, and prior research as well as the present data has shown that adults typically hold views that are very similar to these, concerning how they think that young people ought to act online. On the other hand, youths’ actual online behaviour, as reported in earlier studies, differs considerably from this. In line with this, the students also seemed to endorse a form of private morals view, according to which moral choices are simply up to one’s own taste, which would yield an escape exit from the restrictive views mentioned above, and permit any behaviour. In the discussion, it is argued that this is the result of an attempt at value transmission from the grown-up community, probably including teachers, which might seem to work, since the students claim to hold certain views, but which likely instead constitutes a false security, since these values are not actually accepted, but only paid lip service to, and the adults are therefore wrong in their belief that the students are protected by a certain set of values (that they think the students are upholding), since the students in fact do not uphold, and therefore do not act based upon, these values. This situation risks making the students more vulnerable than had no value transmission attempt been taken in the first place. Hence, the attempted value transmission runs the risk of counteracting its purpose of helping the students acquire a safe online behaviour.Throughout the moral reasoning mentioned above, extensive variations in the students’ reasoning were found, both interpersonally and intrapersonally, both in the decision method and in the rightness criterion dimensions, as well as in between the dimensions. The existence of such variations is a novel finding, and while possible applications in future research are discussed, it is also noted that this existence constitutes a reason to question the successfulness of both the value transmission and the inquiry ethics endeavours of the educational system.The results and discussions described above highlight the importance of investigating the merits of the different approaches. Several arguments that arise from the material of this thesis are presented, evaluated and discussed. The ability of each approach to fulfil some alleged key aims of ethics education is scrutinised; their abilities to educate for good citizenship, to educate for quality of life of the individual, and to facilitate better educational results in other subjects are all investigated, as well as the ability of each approach to help counteract the influence from online extremist propaganda aimed at young people and to promote safe online behaviour in general.It is concluded that the inquiry ethics approach has the strongest support from the material of this thesis. Some consequences for school practice are discussed, and it is concluded that changing the role of ethics in the curriculum would be beneficial, downplaying the role of value transmission and further increasing, and making more explicit and clear, the role of inquiry ethics. It is also shown that there are strong reasons for the inclusion of a new subject in the Swedish compulsory education with special focus on ethics. Some possible causes, and some consequences, of this is discussed.
23.
  • Golling, Stefan (författare)
  • A Study on Microstructure-Dependent Deformation and Failure Properties of Boron Alloyed Steel
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Developments in the automotive industry are driven by customer desires and legislative authorities. Legislation has restricted the emissions standards for vehicles, and has mandated the need for higher safety standards. The emission of carbon dioxide is directly related to fuel consumption, and the reduction in fuel consumption can be achieved by reducing the vehicle mass.A variety of methods have been used to reduce a vehicle’s mass while maintaining its crashworthiness. A technique using low-alloyed boron steel has been developed, and it enables the design of lighter body-in-white, while maintaining passenger safety. The technique is called press-hardening or hot stamping, and it involves the simultaneous forming and quenching of sheet metal. Press-hardened components have superior material properties compared to components made of mild steel. Another feature of compo-nents formed at elevated temperatures is the possibility of tailoring material properties in desired regions of the component. This is realized by using specially designed tools that allow differential in-die cooling rates and thus direct control of the formed microstructure. Using this technique, it is possible to manufacture a high-strength region next to a high-ductility section divided by a transition zone of mixed microstructure.The present work aims to determine the influence of mixed microstructures on the mechanical properties of low-alloyed boron steel. An experimental heat-treatment process is used to form multi-phase microstructures with a variety of phase volume fractions present in the composite. Digital image correlation is used to investigate the deformation of tensile specimens under loading. This full-field technique and a suitable constitutive model enables us to evaluate the flow and fracture properties of heat-treated samples. Microstructural characterization is used to determine the type of phases present and their average volume fraction in the composites.The findings from experimental studies are compared to results predicted by a constitutive model. A modeling strategy is employed to determine the effective material properties depending on the properties of single-phase characteristics. Failure of the material is indicated by stress-based fracture criteria. Numerical issues in finite-element modeling concerning the mesh-size sensitivity are addressed using a regularization method.The results of the experimental work aids the calibration and validation of the proposed microstructure-based modeling approach, and a knowledge of the processing history enables the prediction of the overall hardening behavior and fracture elongation. A comparison of experimental results, which are not used for calibration, with numerical results shows that there is good agreement.
24.
  • Gustafsson, Emil (författare)
  • Design and application of experimental methods for steel sheet shearing
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Shearing is the process where sheet metal is mechanically cut between two tools. Various shearing technologies are commonly used in the sheet metal industry, for example, in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material. The constant development of sheet metals toward higher strength and formability leads to increased forces on the shearing equipment and tools.Shearing of new sheet materials imply new suitable shearing parameters. Investigations of the shearing parameters through live tests in the production are expensive and separate experiments are time consuming and requires specialized equipment. Studies involving a large number of parameters and coupled effects are therefore preferably performed by finite element based simulations. Accurate experimental data is still a prerequisite to validate such simulations. There is, however, a shortage of accurate experimental data to validate such simulations.In industrial shearing processes, measured forces are always larger than the actual forces acting on the sheet, due to friction losses. Shearing also generates a force that attempts to separate the two tools with changed shearing conditions through increased clearance between the tools as result. Tool clearance is also the most common shearing parameter to adjust, depending on material grade and sheet thickness, to moderate the required force and to control the final sheared edge geometry.In this work, an experimental procedure that provides a stable tool clearance together with accurate measurements of tool forces and tool displacements, was designed, built and evaluated. Important shearing parameters and demands on the experimental set-up were identified in a sensitivity analysis performed with finite element simulations under the assumption of plane strain. With respect to large tool clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the tools was constructed.Steel sheets of different strength levels were sheared using the above mentioned experimental set-up, with various tool clearances, sheet clamping and rake angles. Results showed that tool penetration before fracture decreased with increased material strength. When one side of the sheet was left unclamped and free to move, the required shearing force decreased but instead the force attempting to separate the two tools increased. Further, the maximum shearing force decreased and the rollover increased with increased tool clearance.Digital image correlation was applied to measure strains on the sheet surface. The obtained strain fields, together with a material model, were used to compute the stress state in the sheet. A comparison, up to crack initiation, of these experimental results with corresponding results from finite element simulations in three dimensions and at a plane strain approximation showed that effective strains on the surface are representative also for the bulk material.A simple model was successfully applied to calculate the tool forces in shearing with angled tools from forces measured with parallel tools. These results suggest that, with respect to tool forces, a plane strain approximation is valid also at angled tools, at least for small rake angles.In general terms, this study provide a stable symmetric experimental set-up with internal balancing of lateral forces, for accurate measurements of tool forces, tool displacements, and sheet deformations, to study the effects of important shearing parameters. The results give further insight to the strain and stress conditions at crack initiation during shearing, and can also be used to validate models of the shearing process.
25.
  • Gustafsson, Silje (författare)
  • Self-care for Minor Illness: People's Experiences and Needs
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • During later years, the primary care services are experiencing a heavier strain in terms of increasing expenses and higher demand for medical services. An increased awareness about pharmaceutical adverse effects and the global concern of antibiotic resistance has given self-care and active surveillance a stronger position within the primary care services. The management strategy for minor illnesses is important because care-seekers tend to repeat successful strategies from past events, and past experience with self-care drives future self-care practices. The overall aim of this thesis was to explore people’s experiences and needs when practicing self-care and receiving self-care advice for minor illnesses. This was achieved by studying people’s experiences with and knowledge of minor illnesses, self-care interventions and channels of information used when providing self-care for minor illness. Needs for confidence in self-care were studied, as well as supporting and obstructing factors in the practice of self-care. Satisfaction with telephone nursing and people’s experiences of reassurance in relation to the decision-making process in self-care for minor illness was explored. The results showed that experience correlated with self-rated knowledge of the condition, and the least common conditions most often generated a health care services consultation. To confidently practice self-care people needed good knowledge and understanding about obtaining symptom relief. Younger persons more often reported the need of having family or friends to talk to. Easy access to care was most often reported as a support in self-care, and a lack of knowledge about illnesses was most often reported as obstructing self-care. Care-seekers receiving self-care advice were less satisfied with the telephone nursing than care-seekers referred to medical care, and feeling reassured after the call was the most important factor influencing satisfaction. Self-care advice had a constricting influence on healthcare utilization, with 66.1% of the cases resulting in a lower level of care than first intended. The course of action that persons in self-care decided on was found to relate to uncertainty and perception of risk. Reassurance had the potential to allay doubts and fears to confidence, thereby influencing self-care and consultation behavior. In conclusion, symptoms of minor illness can cause uncertainty and concern, and reassurance is an important factor influencing people’s course of action when afflicted with minor illness. The nurse constitutes a calming force, and the encounter between the nurse and the care-seeker holds a unique possibility of reassurance and confidence that minor illness is self-limiting to its nature and that effective interventions can provide relief and comfort. Just as health is more than the absence of disease, self-care is more than the absence of medical care.
26.
  • Hajlane, Abdelghani (författare)
  • Hierarchical cellulosic reinforcement for composites: enhanced resistance to moisture and compatibility with polymers
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Cellulosic fibres (flax, hemp, regenerated cellulose) possess decent mechanical properties and they are gaining interest as an alternative to synthetic reinforcement (e.g. glass fibres) in polymers to reduce the petroleum consumption and pollution. In particular, manmade Regenerated Cellulose Fibres (RCF) have been extensively studied as potential reinforcement in polymer composites. For high performances where stability is highly required, RCF among the cellulosic fibres are well qualified due the advantage of being continuous with regular cross section. However, the hydrophilic character and the sensitivity to moisture reduce the use of fibres based cellulose in composite applications. Indeed, the moisture absorption and the low compatibility leading to weak fibre/matrix interface are major factors behind the less interest of utilizing cellulosic fibres in composite intended for high performances. The short term objective of this thesis was to improve the resistance to moisture and the adhesion of regenerated cellulose fibres (RCF) commercialized under the trade name CORDENKA 700 super 3 to Epoxy matrix through chemical treatments by cellulose nano-crystals via silane coupling agents. In Paper I chemical treatments of cellulose nano-crystals using (CNC) esterification and amidification to attach long aliphatic chains is studied. The treatment was successfully achieved as confirmed by spectroscopic characterisations and led to a decrease of the moisture absorption. Contact angle measurement showed hydrophobic of CNC after treatment. In Paper II, CNC extracted from wastes of date palm tree were grafted on RCF fibres to create hierarchical structure. The effect of grafting CNC on RCF was evaluated by tensile tests both in static and loading-unloading. In fact, treatments were revealed to change slightly the microstructure where the orientation of both crystalline and amorphous phases where re-oriented as X-ray analysis showed. Grafted fibres based unidirectional composite were manufactured and transversally tested. Both mechanical properties and resistance to crack were significantly increased by fibre modification. Another approach for chemical modification of RCF fibres was developed in Paper III. In this paper, the process of modification of RCF by CNC is more environmentally friendly. The γ-methacryloxypropyltrimethoxysilane (MPS) was used as coupling agent to attach the CNC onto the fibres. This treatment involves a mixture of water and ethanol as solvents and was run at relatively low temperature. The impact of the treatment on fibres was scrutinised after each treatment basically by MPS and after grafting CNC. Results showed that the modification by silane decreased the stiffness and strength of fibres while the strain at failure was increased. However, after grafting CNC, stiffness and strain at failure were recovered while the strength remained at the same order of magnitude as for fibres treated only by the coupling agent. The effect of these treatments on moisture absorption and on the adhesion with epoxy matrix was the focus of the Paper IV. In this paper, it was shown that at high relative humidity (RH=64%) the treatment by CNC decreased water uptake by factor of two compare to untreated fibres. Besides, the treatments by CNC at different concentrations lessened the impact of moisture on stiffness and strength of fibres after exposure to the same humidity level (RH=64%). Moreover, the pull-out test performed on fibre bundles showed that the adhesion between fibre and matrix is less affected by moisture (samples conditioned at RH=64%) for CNC grafted fibres compare to untreated fibres. The treatment process by MPS was Scaled-up to Non-Crimp Fabric in Paper V and the interlaminar properties of composites reinforced with RCF were studied. Double cantilevered beam (DCB) test was used to characterize fracture toughness, under static and fatigue loading. Regenerated cellulose fibres exhibit highly nonlinear behaviour and strongly influence the performance of their composites. The obtained fracture toughness values were significantly high compared to those of synthetic fibre reinforced composites. However, due to the high nonlinearity, a concrete conclusion was not easy to make on the effect of fibre treatment on the materials performance. Thus, scanning electron microscopy studies were carried out on fracture surfaces which confirmed the treatment effect, qualitatively, on the improvement of interfacial adhesion.
27.
  • Hernandez, Sinuhe (författare)
  • Friction and Wear Phenomena in Steels at Elevated Temperatures
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Different grades of steels are often exposed to high temperatures whether during their shaping/forming or during their use in several applications. This exposure to high temperature has a great bearing on the resulting friction and wear phenomena in steels due to changes in their surface and near-surface properties. This means that the wear and frictional behaviour will be no longer controlled nor determined by the original properties of steels but rather by the changes in steels surfaces brought about by high temperatures. A thorough understanding of friction and wear phenomena in steels under these conditions is crucial in terms of control as well as prediction of friction and wear. This thesis has focussed on friction and wear phenomena in some selected steels suitable for working at high temperatures.The initial part of this work concentrated on investigating the effect of load and temperature on the friction and wear behaviour of tool steel sliding against boron steel in a pin-on-disc (POD) test configuration. This investigation revealed the formation of oxidised protective layers and their role in reducing wear and friction at elevated temperatures.Experimental studies in a specially designed high temperature tribometer for simulating tool-workpiece interaction in hot sheet metal forming were also carried out using similar conditions to those used in the POD tests. These studies corroborated the presence and importance of oxidised layers at elevated temperatures. However, the thickness of oxidised layers was lower compared to those on the POD specimens. The results showed a good correlation between mechanisms of wear and friction especially at 400 °C. As in the case of the POD studies, the main wear mechanisms were adhesion and three body abrasion.Further, three-body abrasive wear behaviour of different tool steels, heat treated high-Si steels and boron steel at different temperatures was also investigated. The two main wear mechanisms identified were microploughing and microcutting. The results revealed near surface modifications in steel surfaces such as work hardened layers, mechanically mixed layers and recrystallization of ferrite grains. The wear behaviour of different steels was strongly influenced by the occurrence of these transformations as well as changes in mechanical properties like hardness and toughness.Nanoindentation and multiple-pass nanoscratch tests were carried out using a high temperature nanoindenter with a view to investigate the relationship between mechanical properties measured (hardness, fracture toughness, plasticity index) and the tribological behaviour of different tool steels. Higher volume losses were obtained for tool steels with low hardness and high plasticity index values.
28.
  • Holmbom, Martin (författare)
  • High value at low cost Methods for supply chain efficiency
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis deals with four areas of research: Economic lot scheduling problems (ELSP), Order quantities in a production line, Economic remanufacturing problems, and Performance-based logistics (PBL).The overall purpose of this thesis is to explore and develop methods to increase efficiency insupply chains. More specifically, the aims of this research are: [1] to develop a solutionprocedure that finds a feasible minimum cost production schedule for a ’single machine multiproductprocess’, [2] to investigate how the order quantity affects the performance of aproduction line, [3] to investigate how the yield rate affects the economic remanufacturingquantity under different carbon emission regulations, and [4] to summarise previouslyreported benefits and drawbacks of performance-based logistics and to explore critical aspectsof implementation.The results of the research on the first aim include a mapping of the ELSP field over100 years, a mathematical derivation of the inventory holding cost for solutions with unequalproduction periods, and a solution procedure that can be used to minimise production costsand thus enhance efficiency.The research on the second aim contributes to the understanding on how processparameters affect lead time and production rate in a production line. That knowledge can beused as a guideline for how to handle e.g. order quantity, setup time, work in progressrestrictions and cycle time variations to improve the efficiency of a production line.The results of the research on the third aim include a method to calculate the economicremanufacturing quantity under different carbon emission regulations, which remanufacturerscan use to minimise costs and thus enhance efficiency. This research also contributes to theunderstanding of how the economic remanufacturing quantity is affected by varying yieldrate.Finally, the research on the fourth aim contributes to the understanding of the drivingforces and obstacles of PBL and clarifies relationships to other research fields. The researchsheds light on ’hidden’ costs of PBL and emphasises the need for more evidence regarding theprofitability of PBL, since there is an obvious risk that the cost of e.g. mitigating businessrisks exceeds the gains.Keywords: Economic lot scheduling problems, ELSP, Order quantity, Production lot, EOQ,Production line, Lead time, Remanufacturing, Carbon emission regulation, Yield rate,Performance-based logistics, PBL, Performance contracting, Supply chain integration,Operations management.
29.
  • Holmstedt, Elise, 1983- (författare)
  • Modelling Transport of Non-Spherical Particles in Small Channel Flow
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • A model has been developed to predict the movement of oblate and prolate particles on amicro- and nano-scale in laminar channel flow, both for purposes of statistical aggregationand to study motion of single particles. For the purpose of this thesis the model has beenadapted to examine particle deposition patterns in the human lung and the filtration ofparticles during manufacturing of composites, but the possibilities of the model extendto all areas where the particle Stokes and Reynolds numbers are small.To examine the influence the breathing pattern has on the deposition of inhalednano- and micro-fibres deposition rates were compared at different injection points ofthe breathing cycle, where maximum deposition was found when the particles releasedat the beginning of the respiratory cycle while minimum deposition occurred when therelease came at peak inhalation. A comparison between a quasi-steady flow and a cyclicflow was done and it was found that a quasi-steady solution provides a reasonably goodapproximation if the velocity used is a mean of the velocity during the residence time ofthe simulations.A statistical study was done to compare the deposition rates of oblate and prolateparticles of different size and aspect ratio as they travel down narrowing bronchi in asteady, fully developed parabolic flow field. The model shows a clear correlation betweenincreased particle size and increased deposition, it also consistently yielded a higherdeposition rate for oblate particles compared to prolate particles with a similar geometricdiameter. A study of the motion and orientation of single oblate and prolate particleswith large aspect ratio and the same geometric diameter has also been done.In liquid moulding of fibre reinforced composites the resin can be enhanced by nanoandmicro-particles to give the final product additional properties. This is a processthat can be simulated by approximating the gap formed between the fibre bundles to achannel flow with a radially suctioning component caused by the capillary pressure in themicro channels in the bundles. First this flow field is described with a radial componentthat is constant over the length of the channel and compared with a flow purely drivenby an applied pressure gradient without radial forces. Particle size showed a small butstill noticeable influence, particularly for larger particles under the influence of gravity.The second flow field used is time dependent where the flow front in the bundlesand channel mimics that of previous observations. There is initially a period where theflow front in the channel is leading but the radial capillary fluid transport causes thisto retreat and be overtaken by the flow front in the bundles. Particles mixed in theresin will in general travel with a velocity greater than that of the fluid front until theradial velocity component at that point filters the particles by transporting them to thechannel wall. Particle geometry has a smaller impact on the deposition rates in compositemanufacturing than in inhalation since the effect of Brownian forces and gravity are muchsmaller, although there is still some discernible patterns such as a higher deposition ratefor spherical particles during the transport to the flow front.
30.
  • Hooshmand, Saleh (författare)
  • Processing of continuous fibers based on nanocellulose: Influence of dispersion and orientation on mechanical properties
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The aim of the work was to prepare continuous bio-based fibers where nano-sized cellulose was used to improve the mechanical properties. Two different strategies were used to reach this aim, melt-spinning of thermoplastic fibers reinforced with nanocellulose and dry-spinning of cellulose nanofibers without solvent or chemicals. In the first strategy, melt-spun fibers were reinforced with cellulose nanocrystals. First, nanocomposite fibers of cellulose acetate butyrate (CAB) reinforced with cellulose nanocrystals (CNC) and plasticized with triethyl citrate (TEC) were prepared. Two different techniques for dispersing CNC were compared: a process of solvent exchange of the aqueous CNC suspension to ethanol by centrifugation and sol-gel process. The mechanical properties and microscopy results indicated that the sol-gel process enhanced the dispersion. Subsequently the effect of CNC concentration and solid-state drawing (SSD) was studied. The results were defect-free and smooth fiber surfaces, in which an addition of 10 wt% CNC and drawing increased the tensile strength and Young’s modulus by 43% and 134% compared to the as-spun unreinforced fibers. This melt spinning process was also used to process melt-spun nanocomposite fibers of polylactic acid (PLA) and CNC. In this study the effect of surface modification of the CNC as well as the melt draw ratio (MDR) was investigated. The results showed that the increased MDR together with the surface modification resulted in better mechanical properties. In the second strategy, continuous fibers of native cellulose nanofibers (CNF) were prepared by dry-spinning. First, the effect of the spinning rate and the CNF concentration on the mechanical properties were investigated. The highest orientation and mechanical properties were achieved by combining a low CNF concentration with a high spin rate. The modulus of the fibers increased from 7.7 to 12.6 GPa and the strength form 131 to 222 MPa. After this, to further improve the orientation of the CNF, a small amount of hydroxyethylene cellulose (HEC) was used as a binder and the fibers were cold drawn after the spinning. The results showed that the addition of the binder and cold drawing increased the modulus and strength by 76% and 73% being 15 GPa and 260 MPa respectively. The results also confirmed that dry-spinning has potential for up-scaling, providing a continuous fiber production with well-controlled speed.These studies demonstrated that the dispersion and alignment of nanocellulose in spun fibers play key roles in improving the mechanical properties of these continuous bio-based fibers.
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