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  • 1.
    Farid, Touaiti
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Chemical Engineering Department, Faculty of Science and Technology, University of Ghardaia.
    Herrera Vargas, Natalia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Investigation of crystalline structure of plasticized poly (lactic acid)/Banana nanofibers composites2018In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 369, article id 012031Article in journal (Refereed)
    Abstract [en]

    Polylactic acid (PLA) is a promising biodegradable candidate to replace synthetic commodity plastics in many applications. However, this polymer shows high brittleness, slow rate and lower degree of crystallization. The addition of plasticizing agents can enhance the toughness, but its effects on the crystallization behavior remain inconclusive. Therefore, this research is aiming to cast light on this area. Using differential scanning calorimetry (DSC) at a 2°C/min cooling rate, extruded neat PLA samples showed lower degree of crystallinity and thermal stability. This material shows cold crystallization upon heating and does recrystallize prior melting. These results indicate a clear instability in the crystalline state are confirmed by the crystallographic results by the X-ray diffractions (XRD) pattern and atomic force microscopic imagery. The addition of around 20 wt% of glycerol triacetate (GTA) with 1wt% of banana nanofibers (BNF) almost doubled the crystallinity. This modification is believed to occur through a dilution mechanism in order to increase crystallization rate yielding a more stable crystalline structure as shown by the XRD. However, the dynamic mechanical thermal analysis (DMTA) showed a 30 to 50% reduction in the room temperature storage modulus (stiffness) is in plasticized samples when compared to neat 100% PLA. Although these results shows the possibility to enhance the crystallization through a combination of plasticizing and nanoreinforcing effects, further studies is still needed to optimize the material formulation in order to find the best ratios to secure both a good crystallization and mechanical properties. This will definitively result in a new material that can be used for current and futuristic applications.

  • 2.
    Haque, Md. Minhaz-Ul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Herrera, Natalia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu, Finland.
    Melt compounded nanocomposites with semi-interpenetrated network structure based on natural rubber, polyethylene, and carrot nanofibers2018In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 135, no 10, article id 45961Article in journal (Refereed)
    Abstract [en]

    The present study deals with the processing and characterization of cellulose nanocomposites natural rubber (NR), low-density polyethylene (LDPE) reinforced with carrot nanofibers (CNF) with the semi-interpenetrated network (S-IPN) structure. The nanocomposites were compounded using a co-rotating twin-screw extruder where a master-batch of NR and CNF was fed to the LDPE melt, and the NR phase was crosslinked with dicumyl peroxide. The prepared S-IPN nanocomposites exhibited a significant improvement in tensile modulus and yield strength with 5 wt % CNF content. These improvements are due to a better phase dispersion in the S-IPN nanocomposites compared with the normal blend materials, as demonstrated by optical microscopy, electron microscopy and ultraviolet–visible spectroscopy. The S-IPN nanocomposite also displayed an improved crystallinity and higher thermal resistance compared with NR, CNF, and the normal blend materials.

  • 3.
    Herrera Vargas, Natalia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Processing and properties of nanocomposites based on polylactic acid, chitin and cellulose2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The production of bio-based and biodegradable nanocomposites has gained attention during recent years for environmental reasons; however, the large-scale production of these nanocomposites still poses challenges. The objective of this work has been to prepare bio-based and biodegradable nanocomposites via liquid-assisted extrusion and to gain a deeper understanding of the process and the relationship between the process, composition, structure and properties. Extrusion is a common industrial process and thus, the development of this technique for the preparation of bionanocomposites can promote the commercialization of these materials in future.

    In this work, nanocomposites based on polylactic acid (PLA), cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and chitin nanocrystals (ChNC) with varying nanomaterial content were prepared via liquid-assisted extrusion using a plasticizer as a dispersing and processing aid. This process consists of dispersing the nanomaterial in a liquid composed of water, a plasticizer and/or a solvent, and then feeding this suspension directly into the extruder during the process. To be able to carry out this process successfully, parameters such as the amount of liquid, the liquid feeding rate or the water-to-solvent ratio, among others, should be taken in account.

    CNF and ChNC were produced from banana rachis waste and crustacean waste, respectively, whereas CNC were available as a commercial product. Glycerol triacetate (GTA) and triethyl citrate (TEC) were used as plasticizers, dispersing and processing aids. The effects of the liquids used during extrusion, the plasticizers and the nanomaterials in the PLA properties were studied. Furthermore, the effects of the cooling rate during the compression molding and the solid-state drawing on the properties of the PLA nanocomposites were investigated. Additionally, the effect of ChNC on the processing and properties of blown films was evaluated.

    The results presented in this work demonstrated that the use of water and a solvent during the liquid-assisted extrusion did not decrease the molecular weight of the PLA. It was also found that the feeding of nanomaterials in aqueous or aqueous/solvent suspension resulted in PLA micro-composite with lower mechanical properties than PLA. However, when a nanomaterial was fed together with a plasticizer, its dispersion and distribution into the PLA were progressively improved with increasing plasticizer content. The plasticized PLA nanocomposites showed improved properties compared to their respective counterpart without nanomaterials when the plasticizer content was ≥7.5 wt%. Furthermore, it was demonstrated that the properties of PLA can be tailored through the composition of the nanocomposite or during the processing. It was observed that the modification of PLA with only plasticizer in high amounts (20 wt%) resulted in enhanced elongation at break and toughness but it had negative effects on the thermal and mechanical properties; however, the incorporation of nanomaterials minimized these effects. The addition of a small amount of nanomaterial (1 wt%), either CNF, CNC or ChNC, to plasticized PLA resulted in enhanced mechanical properties. It was also demonstrated that the cooling rate during compression molding and the solid-state drawing significantly affected the crystallinity of the PLA nanocomposites and, thus, their final properties. The fast cooling rate during compression molding resulted in more flexible and transparent materials than when a slow cooling rate was used, and as a result, PLA films with different mechanical properties were obtained. The drawing of the PLA/CNF nanocomposite at a drawing temperature slightly above the Tg, a high draw speed and at the highest drawing ratio, resulted in the highest mechanical properties. It was also found that the increased toughness after adding CNF to the plasticized PLA or after drawing the PLA/CNF nanocomposite, was attributed to the occurrence of massive crazing effect as a result of the presence of CNF and its effect on the crystallinity and/or on the spherulite growth. Finally, 6 kg of plasticized PLA nanocomposite with 5 wt% of ChNC was prepared and used as a masterbatch to produce bio-nanocomposite blown films. The nanocomposite material showed easier processability during the film-blowing process when compared with the reference material without nanocrystals. In addition, the nanocomposite blown films exhibited higher tear and puncture strength, lower fungal activity and lower electrostatic attraction properties, which are favorable in packaging applications. 

    In conclusion, this thesis shows that the liquid-assisted extrusion process is an excellent approach for producing PLA nanocomposites using cellulose and chitin nanomaterials. The results indicated that the addition of these nanomaterials, together with a plasticizer and further processing, can result in PLA nanocomposites with varied properties that can be used for packing applications. It was also shown that the processing technique presented can be a step forward for the large-scale production of bionanocomposites.

     

  • 4.
    Herrera Vargas, Natalia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Project: Renewable eco-friendly Poly(Lactic acid) nanocomposites from waste sources2014Other (Other (popular science, discussion, etc.))
  • 5.
    Herrera Vargas, Natalia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Singh, Anshu Anjali
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Salaberria, Asier M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Faculty of Engineering, Guipúzcoa, University of the Basque Country.
    Labidi, Jalel
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Faculty of Engineering, Guipúzcoa, University of the Basque Country.
    Mathew, Aji P.
    Division of Materials and Environmental Chemistry, Stockholm University.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu.
    Triethyl Citrate (TEC) as a Dispersing Aid in Polylactic Acid/Chitin Nanocomposites Prepared via Liquid-Assisted Extrusion2017In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 9, no 9, article id 406Article in journal (Refereed)
    Abstract [en]

    The production of fully bio-based and biodegradable nanocomposites has gained attention during recent years due to environmental reasons; however, the production of these nanocomposites on the large-scale is challenging. Polylactic acid/chitin nanocrystal (PLA/ChNC) nanocomposites with triethyl citrate (TEC) at varied concentrations (2.5, 5.0, and 7.5 wt %) were prepared using liquid-assisted extrusion. The goal was to find the minimum amount of the TEC plasticizer needed to enhance the ChNC dispersion. The microscopy study showed that the dispersion and distribution of the ChNC into PLA improved with the increasing TEC content. Hence, the nanocomposite with the highest plasticizer content (7.5 wt %) showed the highest optical transparency and improved thermal and mechanical properties compared with its counterpart without the ChNC. Gel permeation chromatography confirmed that the water and ethanol used during the extrusion did not degrade PLA. Further, Fourier transform infrared spectroscopy showed improved interaction between PLA and ChNC through hydrogen bonding when TEC was added. All results confirmed that the plasticizer plays an important role as a dispersing aid in the processing of PLA/ChNC nanocomposites.

  • 6.
    Oksman, Kristiina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jonoobi, Mehdi
    Hietala, Maiju
    Vargas, Natalia Herrera
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cellulose nanocomposites processing using extrusion2013In: Production and Applications of Cellulose Nanomaterials, TAPPI Press, 2013, p. 99-102Chapter in book (Refereed)
    Abstract [en]

    We have been working with development of compounding extrusion process for cellulose nanocomposites, since 2003. Feeding and dispersion of the nanocellulose materials are the main challenges and we have developed two specific processing routes; i) liquid feeding of the nanomaterials into the extruder and ii) dry feeding of nanomaterials as a master batch, to address the feeding problem. Composites with aggregated, partially dispersed or fully dispersed nanocellulose crystals or fibers have been obtained depending on the extent of the separation of cellulose nanocrystals or nanofibers in the liquid medium or in the master batch and the interaction of nanocelluloses with the polymer matrix. We aim to produce nanocomposites with good mechanical properties, thermal stability and transparency and at the same time develop an energy efficient and cost effective processing methodology, which can be up-scaled in industrial level.

  • 7.
    Pelcastre, Leonardo
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vargas, Natalia Herrera
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the damage mechanisms of form fixture hardening tools2012In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 25, p. 219-226Article in journal (Refereed)
    Abstract [en]

    In metal forming operations such as form fixture hardening, the interaction between the tools and the work-piece is strongly influenced by the tribological properties at the interface. Damage or excessive wear of the tools can be detrimental to the quality of the final component and it also has an impact on the process economy due to increased maintenance or more frequent replacement of tools. The objective of this study was to investigate the damage mechanisms encountered in real form fixture hardening tools in order to understand the causes of tool failure and ultimately to come up with possible solutions for this problem.Advanced techniques such as Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) were used for obtaining an in-depth understanding of the different phenomena involved in the failure of form fixture hardening tools. Two different tools having different hardness values and microstructures that had been used in production were analysed.The damage mechanisms found included abrasive and adhesive wear, material transfer, corrosion and mechanical and thermal fatigue. The main damage mechanism was found to be cracking caused by mechanical stresses on the surface. Although both tools presented similar types of damage, the severity was different and it was strongly influenced by the microstructure.

  • 8.
    Singh, Anshu A.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Herrera Vargas, Natalia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions2018In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 104, p. 101-107Article in journal (Refereed)
    Abstract [en]

    Aligned nanocomposite tapes based on plasticized polylactic acid (PLA) and 1 wt.% cellulose nanofibers (CNF) were prepared using uniaxial solid-state drawing, and the effects of drawing conditions including temperature, speed and draw ratio on the material were studied. Microscopy studies confirmed alignment and the formation of ‘shish-kebab’ morphology in the drawn tape. Mechanical properties demonstrate that the solid-state drawing is a very effective way to produce stronger and tougher PLA nanocomposites, and the toughness can be improved 60 times compared to the undrawn tape. Additionally, the thermal properties, i.e. storage modulus, glass transition temperature and degree of crystallinity were improved. These improvements are expected due to the synergistic effect of CNF in the nanocomposite and orientations induced by the solid-state drawing.

  • 9.
    Singh, Anshu A.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wei, Jiayuan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vargas, Natalia Herrera
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu.
    Synergistic effect of chitin nanocrystals and orientations induced by solid-state drawing on PLA-based nanocomposite tapes2018In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 162, p. 140-145Article in journal (Refereed)
    Abstract [en]

    Uniaxial solid-state drawing was used to orientate plasticized polylactic acid (PLA) and its nanocomposite tapes with 1 and 5 wt% chitin nanocrystals (ChNC). Microscopy studies confirmed the orientation and formation of a ‘shish-kebab’ morphology in the drawn tapes. The mechanical properties demonstrated that the drawing led to stronger and tougher nanocomposites compared to plasticized PLA. The tensile strength increased from 41 MPa to 71 MPa, and the elongation at break increased from 5% to 60% for the nanocomposite with 5 wt% ChNC and a draw ratio of 3. The ChNC had a positive effect on the thermomechanical properties; the tan delta peak shifted to a higher temperature with an increasing ChNC content. These improvements in the mechanical and thermal properties are expected synergistic effects of both the ChNC in the nanocomposite and the alignment of the ChNC together with the polymer chains induced by the solid-state drawing.

  • 10.
    Vargas, Natalia Herrera
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Processing and Properties of Nanostructured Biocomposites2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this work, nanostructured biocomposite fibers and films with cellulose nanofibers (CNF), cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using solutions mixing followed by electrospinning and melt compounding. The main processing challenges for these materials were to find parameters for: 1) fiber alignment in electrospinning, 2) feeding the nanomaterials into the extruder and 3) dispersion and distribution of the nanomaterials in the polymeric matrix. This thesis consists of three publications, which are summarized below.The first study was about random and aligned cellulose fibers prepared by electrospinning. Cellulose acetate (CA) was used as a matrix and a mixture of acetic acid and acetone (1:1) was used as a solvent. CNC with different concentrations (0–5 wt-%) were used as reinforcement. Microscopy studies showed fibers with smooth surfaces, different morphologies and diameters ranging between 200 and 3300 nm. It was found that the fiber diameters decreased with increased CNC contents. The microscopy studies also indicated well-aligned fibers. Results from dynamic mechanical thermal analysis indicated improved mechanical properties with the addition of CNC. The storage modulus of electrospun CA fibers increased from 81 to 825 MPa for fibers with 1 wt% CNC at room temperature. X-ray analysis showed that the electrospun CA fibers had a crystalline nature and that there was no significant change in crystallinity with the addition of CNC.In the second study, polylactic acid (PLA) and its nanocomposite based on CNF and glycerol triacetate (GTA) were prepared using a co-rotating twin-screw extruder. GTA was used as a plasticizer, a processing aid to facilitate nanofiber dispersion and as a liquid medium for feeding. The optical, thermal and mechanical properties were characterized and the toughening mechanism was studied. The addition of GTA (20%) and CNF (1%) resulted in increased degree of crystallinity and thus decreased optical transparency. Furthermore, these additives showed a positive effect on the elongation at break and toughness, which increased from 2 to 31% and from 1 to 8 MJ/m3, respectively. A combination of nanofiber-matrix interfacial slippage and a massive crazing effect is suggested for PLA toughening. CNF were expected to restrict the spherulite growth and therefore enhance the craze nucleation. In the third study, triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using a co-rotating twin-screw extruder. The materials were compression molded to films using two different cooling rates. The cooling rates and the addition of nanocrystals (1 wt%) had an impact on the crystallinity as well as the optical, thermal and mechanical properties of the films. The fast cooling resulted in more amorphous materials, increased transparency and elongation to break, (approx. 300%) when compared with slow cooling. Chitin nanocomposites were more transparent than cellulose nanocomposites; however, microscopy study showed presence of agglomerations in both materials. The mechanical properties of the plasticized PLA were improved with the addition of a small amount of nanocrystals resulting in PLA nanocomposites suitable for use in film blowing and thus packaging applications. Summing up, this thesis shows that solution mixing followed by electrospinning can be used to produce reinforced green nanocomposite fibers with random or aligned orientation with, probably, potential to be used in membranes, filters or even in medical applications. It was also shown that PLA-CNF nanocomposites can be prepared using extrusion and liquid feeding and that small amounts of CNF changed the fracture mechanism, resulting in increased toughness. In addition, the cooling rate of the plasticized PLA and its nanocomposite films was found to significantly impact the film properties.

  • 11.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hooshmand, Saleh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Spinning of continuous biofibers reinforced with cellulose nanocrystals2013In: Production and Applications of Cellulose Nanomaterials, TAPPI Press, 2013, p. 115-118Chapter in book (Refereed)
    Abstract [en]

    Our aim has been to produce continuous biofibers and use nanocrystals to improve the properties. Cellulose nanocomposite fibers were prepared by melt spinning of cellulose acetate butyrate (CAB), cellulose nanocrystals (CNCs) and triethyl citrate (TEC) as well as electro spinning of cellulose acetate (CA) and CNCs. Different characterization techniques such as tensile testing, DMA, TGA, SEM and AFM were used to study the properties of the obtained nanocompiste fibers. The results showed that sol-gel technique successfully dispersed CNCs in the CAB matrix, therefore; an improvement in the mechanical properties of the melt spun bionanocomposite fibers were achieved. Likewise, the addition of CNCs into CA matrix generated an improvement in the storage modulus of the random oriented electrospun fibers. Aligned CA- fibers and nanocomposite fibers were successfully electrospun. A tendency to decrease the fiber diameter with the addition of CNCs was found for the both types of electrospun nanocomposite fibers.

  • 12.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Manufacturing tougher PLA by the liquid feeding of cellulose nanofiberes and plasticizer2014In: SPE Proceeding ANTEC2014, Society of Plastics Engineers Incorporated (SPE) , 2014Conference paper (Refereed)
    Abstract [en]

    A polylactic acid (PLA) nanocomposite with 9 times higher toughness than neat PLA was prepared by compounding extrusion using cellulose nanofibers (CNFs) as an additive and glycerol triacetate (GTA) as a plasticizer. Liquid feeding was used to incorporate the CNFs and the liquid plasticizer into the extruder. Both additive and plasticizer were used to improve the PLA toughness and the plasticizer was also used to facilitate the dispersion and distribution of CNFs in the PLA matrix

  • 13.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Plasticized polylactic acid/cellulose nanocomposites prepared using melt-extrusion and liquid feeding: Mechanical, thermal and optical properties2015In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 106, p. 149-155Article in journal (Refereed)
    Abstract [en]

    Plasticized polylactic acid (PLA) and its nanocomposite based on cellulose nanofibers (CNF) and glycerol triacetate (GTA) were prepared using a co-rotating twin-screw extruder. GTA was used as a plasticizer, a processing aid to facilitate nanofiber dispersion and as a liquid medium for their feeding. The optical, thermal and mechanical properties were characterized and the toughening mechanism was studied. The addition of GTA (20%) and CNF (1%) resulted in increased degree of crystallinity and decreased optical transparency. Furthermore, these additives showed a positive effect on the elongation at break and toughness, which increased from 2 to 31% and from 1 to 8 MJ/m3, respectively. The combination of slippage of the nanofiber-matrix interface and a massive crazing effect as a result of the presence of CNF is suggested for PLA toughening. CNF were expected to restrict the spherulite growth and therefore enhance the craze nucleation.

  • 14. Vargas, Natalia Herrera
    et al.
    Mathew, Aji P.
    Wang, Luyi
    Luleå tekniska universitet.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Randomly oriented and aligned cellulose fibres reinforced with cellulose nanowhiskers and prepared by electrospinning2011In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 40, no 2, p. 57-64Article in journal (Refereed)
    Abstract [en]

    The goal of this work was to prepare random and aligned cellulose fibres by electrospinning. Cellulose acetate (CA) was used as a matrix and a mixture of acetic acid and acetone (1:1) was used as an solvent. Cellulose nanowhiskers (CNWs) with different concentrations (0-5 wt-%) were used as reinforcement. Microscopy studies showed fibres with smooth surfaces, different morphologies and diameters ranging between 200 and 3300 nm. It was found that the fibre diameters decreased with increased CNW contents. The microscopy studies also indicated well aligned fibres. Results from dynamic mechanical thermal analysis indicated improved mechanical properties with the addition of CNWs. The storage modulus of electrospun CA fibres increased from 81 to 825 MPa for fibres with 1 wt-% CNW at room temperature. X-ray analysis showed that the electrospun CA fibres had a crystalline nature and that there was no significant change in crystallinity with the addition of CNWs

  • 15.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Roch, Hendrik
    Department Bio-based Plastics, Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT, Osterfelder Straße 3, 46047 Oberhausen.
    Salaberria, Aiser M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Pino, Maxomilano A.
    Macromolecules group, Faculty of Chemistry, Pontifical Catholic University of Chile, Avenida Libertador Bernardo O Higgins 340, Santiago.
    Labidi, Jalel
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Fernandes, Susana M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Radic, Deodato
    Macromolecules group, Faculty of Chemistry, Pontifical Catholic University of Chile, Avenida Libertador Bernardo O Higgins 340, Santiago.
    Lieva, Angel
    Macromolecules group, Faculty of Chemistry, Pontifical Catholic University of Chile, Avenida Libertador Bernardo O Higgins 340, Santiago.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Functionalized blown films of plasticized polylactic acid/chitin nanocomposite: Preparation and characterization2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 92, p. 846-852Article in journal (Refereed)
    Abstract [en]

    Bionanocomposite films prepared with melt compounding and film blowing were evaluated for packaging applications. The nanocomposite masterbatch with 75 wt% polylactic acid (PLA), 5 wt% chitin nanocrystals (ChNCs) and 20 wt% glycerol triacetate plasticizer (GTA) was melt compounded and then diluted to 1 wt% ChNCs with PLA and polybutylene adipate-co-terephthalate (PBAT) prior to film blowing. The morphological, mechanical, optical, thermal and barrier properties of the blown nanocomposite films were studied and compared with the reference material without ChNCs. The addition of 1 wt% ChNCs increased the tear strength by 175% and the puncture strength by 300%. Additionally, the small amount of chitin nanocrystals affected the glass transition temperature (Tg), which increased 4 °C compared with the reference material and slightly enhanced the films degree of crystallinity. The chitin nanocomposite also had lower fungal activity and lower electrostatic attraction between the film surfaces; leading to easy opening of the plastic bags. The barrier and optical properties as well as the thermal degradation of the films were not significantly influenced by the addition of chitin nanocrystals.

  • 16.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Roggio, Giovanni
    Luleå University of Technology.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Extrusion of PLA nanocomposites using liquid feeding of cellulose/chitin nanocrystals2014Conference paper (Refereed)
    Abstract [en]

    In the current study, poly lactic acid (PLA) composites based on cellulose and chitin nanocrystals were prepared by compounding extrusion using liquid feeding. Triacetate citrate (TEC) was used as additive to facilitate the dispersion and distribution of the nanocrystals as well as liquid vehicle to incorporate them into the extruder. Each nanocrystals material was first dispersed in specific amount of ethanol and then mixed with a fixed amount of TEC in order to prepare nanocomposites with 5 wt% of nanocrystals and 20 wt% of TEC. The prepared nanocomposites were compression molded to films and then characterized. The morphology and the mechanical properties were studied. From the point of view of processing, the liquid feeding of nanocrystals was possible; however some agglomerations were observed but even that the mechanical properties of the plasticized PLA were improved.

  • 17.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Roggio, Giovanni
    Luleå University of Technology.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Toughening of cellulose nanofiber films2014Conference paper (Refereed)
    Abstract [en]

    Cellulose nanofibers (CNF) forms strong and stiff films but the toughness of the films needs to be improved if foldable applications are of interest. Preliminary results have shown that the use of plasticizers can increase the toughness of cellulose nanofiber composites. Investigated in this study is the mechanism behind this effect. Different plasticizers with different molecular weights are used to improve the flexibility of the cellulose nanofiber films. Cellulose nanofiber suspensions with varied plasticizer contents are prepared and the films are produced by vacuum filtering and pressing. The toughening effect of the used plasticizers on the CNF films is studied using tensile and falling weight impact testing. This toughening is related to the film morphology using high resolution scanning electron microscopy (HR-SEM) and to the individual CNF surface using atomic force microscopy (AFM).

  • 18.
    Vargas, Natalia Herrera
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Salaberria, Aiser M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Plasticized polylactic acid nanocomposite films with cellulose and chitin nanocrystals prepared using extrusion and compression molding with two cooling rates: effects on mechanical, thermal and optical properties2016In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 83, p. 89-97Article in journal (Refereed)
    Abstract [en]

    Triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using a twin-screw extruder. The materials were compression molded to films using two different cooling rates. The cooling rates and the addition of nanocrystals (1 wt%) had an impact on the crystallinity as well as the optical, thermal and mechanical properties of the films. The fast cooling resulted in more amorphous materials, increased transparency and elongation to break, (approx. 300%) when compared with slow cooling. Chitin nanocomposites were more transparent than cellulose nanocomposites; however, microscopy study showed presence of agglomerations in both materials. The mechanical properties of the plasticized PLA were improved with the addition of a small amount of nanocrystals resulting in PLA nanocomposites, which will be further evaluated for film blowing and thus packaging applications.

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