Ändra sökning
Avgränsa sökresultatet
1 - 7 av 7
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Grubbström, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing and properties of silane crosslinked wood-polyethylene composites2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Utilizing wood as filler and reinforcement in thermoplastic polymer-matrix composites, has gained interest during the last decades, mainly as profile extruded exterior building products such as deck boards, railings, and door- and window frame components. This thesis deals with silane-crosslinking of wood-polyethylene composites through reactiveextrusion. The reactive-extrusion aims to graft silanes to the polyethylene in the moltenphase using peroxide as initiator, and a subsequent curing in high humidity and elevated temperature results in crosslinking of the wood-composite. The goal of using this method is to increase the materials strength, toughness and resistance to creep. Long-term mechanical performance is an issue for wood composites of commonly used thermoplastic matrices and improvements of properties may make these composites applicable as primary load-bearing members in structures. The extrusion process, whereonly grafting of silanes should take place, has earlier shown to be difficult for a wood composite, leading to unintentional crosslinking (scorch) in the melt and thereby poor processability of the composite. The objective for this study was to investigate how to control this reactive-extrusion process for wood-polyethylene composites, by studying process-structure relations, and furthermore to understand the relationship between structure and properties of the composites. The process was investigated by use of different material compositions (papers I-III), curing modes (papers I-III) and extrudersettings (paper IV). The structure-properties relations were studied by use of various test and analysis methods (papers I-V). It was found that the process can be controlled such that scorch was suppressed, and the efficiency of curing was increased. Significant differences on the results were shown for extruder-variables like barrel heat, screw speed and screw configurations. The peroxideload in the grafting step also showed a strong effect. Consequently, a composite not scorched and effectively cured could be obtained, and it was concluded that the complexity of this process, in comparison to the silane-crosslinking of a neat polyethylene, is due to the hydrophilic wood present in the process. All crosslinked composites in this study have improved in strength, toughness and creep resistance, compared to a non-crosslinked counterpart. Not scorched composites showed highest strength, toughness and resistance to creep, despite a lower degree of crosslinking in the matrix after curing, compared to highly scorched samples. To investigate the mechanisms leading to properties improvement, dynamic-mechanical analysis and adhesion tests were employed. It showed that direct chemical bonding between wood and matrix polymer is plausible, but do not describe the mechanism for improvements. A model of interphase for silane-crosslinked wood-polyethylene composites was presented, where it was suggested that the wood particles become surface-treated in the extrusion process, leading to an interphase of more efficient stress transfer. Nothing proves that pure chemical bonding between the wood and polyethylene answers to the strength improvements of the silane-crosslinked composites. It was suggested that future work in this field, in terms of processing, should address the use of ethylene-vinyl-silane copolymers (EVS) or blends of polyethylene and EVS, to obviate the silane-grafting step in the process. However, since the bonds of this crosslinking (-Si-O-Si-) are reversible hydrolysable, the long-term stability should be evaluated. For only stabilizing the matrix polymer, crosslinking by use of peroxides only, may be a better option.

  • 2.
    Grubbström, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Reactive extrusion of wood-thermoplastic composites2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The interest in Wood-thermoplastic composites (WPCs) has increased during the last decades. WPCs are commonly used as building material for decking and railing because of its low need of maintenance. Wood is a renewable resource of good mechanical properties and this make wood fibers interesting to use as reinforcement in a thermoplastic composite. A drawback with this type of composite is the poor long-term mechanical properties which limit its field of applications. The objective of this work was to optimize the process and understand structure-property relations of silane-crosslinked WPCs produced in a one-step reactive extrusion. The specific goal of crosslinking the composite was to improve the interfacial strength and stabilize the polymer matrix in order to improve these composites long-term mechanical properties.Silane-crosslinked WPC was produced by adding wood flour, polyethylene and a silane-peroxide solution to a compounding extruder. The composites were thereafter conditioned in different environments to promote the formation of silane-crosslinks. Parameters like wood flour moisture content, amount/composition of silane-peroxide solution and different general types of polyethylene was studied and related to the efficiency of the process.It was found that silane-technology applied to WPCs can be optimized in terms of processability and achieved property improvements. All crosslinked composites in this study have improved in strength, toughness and creep resistance but it was shown that the tested parameters have affect on both processing and properties. A gentle use of peroxides in the process was concluded to be positive for both processability and resulting property improvements. The unintentional crosslinking in the extrusion process is a drawback but was limited by lower peroxide concentrations. The use of low density polyethylene as polymer matrix lead to twice as high crosslinking rate compared to a high density polyethylene matrix. However, too excessive moisture uptake in the composites appears to lower the efficiency of crosslinking. Future studies should evaluate long-term load behavior more thoroughly and also investigate the conditioning step more carefully.

  • 3.
    Grubbström, Göran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Silane-crosslinking of recycled low-density polyethylene/wood composites2010Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, nr 5, s. 678-683Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this work was to study silane-crosslinking of recycled low-density polyethylene wood composites and its effect on composites properties. The composites were produced in a one-step twin-screw extrusion process and the silane-peroxide solution was pumped into the extruder. Degree of crosslinking, mechanical properties, short-term creep, fractured surfaces and nature of crosslinking were studied to understand the relationship between composite structure and properties. The results showed that crosslinked composite strength, toughness and creep resistance were improved compared to uncrosslinked composites. The flexural strength was doubled compared to uncrosslinked samples and the creep strain was reduced. The crosslinked composites stored under room conditions showed the highest strength, whereas storage in a sauna resulted in a higher degree of crosslinking. The Fourier transform infrared spectroscopy indicated formation of silane-bridges between wood and polyethylene, accordingly improving the interfacial adhesion between the wood and LDPE. The low concentration of peroxide in the silane-solution was shown to be a preferred composition to limit unintentional crosslinking during the process.

  • 4. Grubbström, Göran
    et al.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of wood flour moisture content on the degree of silane-crosslinking and its relationship to structure property relations of wood-thermoplastic composites2009Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, nr 7-8, s. 1045-1050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this work was to examine how the moisture content of wood flour affects the degree of crosslinking when producing silane-crosslinked wood-thermoplastic composites. Crosslinked composites were produced by adding a silane solution to the compounding process of wood flour and polyethylene. Crosslinked composites of pre-dried as well as non-dried wood flour were prepared and their degree of crosslinking at various storage conditions was determined. Mechanical properties and the creep response of the crosslinked composites were tested in order to establish structure-properties relations. The results showed that all crosslinked composites displayed higher strengths and lower creep responses compared with non-crosslinked control samples. However, the degree and rate of crosslinking proved to be lower when a larger amount of moisture was present in the compounding process. It was concluded that the silane-grafting yield was lower when wood flour of a higher moisture content was used.

  • 5. Grubbström, Göran
    et al.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Silane-crosslinking efficiency in wood-polyethylene composites: study of different polyethylenes2010Ingår i: 10th International Conference on Wood & Biofiber Plastic Composites and Cellulose NanoComposites Symposium, Forest Products Society, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective of this work was to examine how the moisture content of wood flour affects the degree of crosslinking during the fabrication of silane-crosslinked wood-thermoplastic composites. Crosslinked composites were produced by adding a silane solution to the compounding process of wood flour and polyethylene. Crosslinked composites of pre-dried as well as non-dried wood flour were prepared and their degree of crosslinking at various storage conditions was determined. Mechanical properties and the creep response of the crosslinked composites were tested in order to establish structure-properties relations. The results showed that all crosslinked composites displayed higher strengths and significantly lower creep responses as opposed a non-crosslinked control sample. However, the degree and rate of crosslinking proved to be lower when a larger amount of moisture was present in the compounding process. It was concluded that the silane-grafting yield was lower when wood flour of a higher moisture content was used, and a possible reason for this was that the radicals necessary for grafting the silanes to the polyethylene had been consumed in the process.

  • 6. Hietala, Maiju
    et al.
    Grubbström, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Use of wood chips in extrusion of wood plastics composites2009Konferensbidrag (Övrigt vetenskapligt)
  • 7.
    Suopajärvi, Terhi
    et al.
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Mathew, Aji P.
    Kekäläinene, Kaarina
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Grubbström, Göran
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Laitinen, Ossi
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Niinimäki, Jouko
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Comparison of two refining methods in production of microfibrillar cellulose: kinetics of refining and energy consumption2010Ingår i: International Paperworld, ISSN 1615-1720, nr 12, s. 10-13Artikel i tidskrift (Refereegranskat)
1 - 7 av 7
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf