Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Processing and properties of nanocomposites based on polylactic acid, chitin and cellulose
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. (Trä och bionanokompositer)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The production of bio-based and biodegradable nanocomposites has gained attention during recent years due to 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; 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 in 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 liquids, 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 nanocrystals 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 and at the highest drawing ratio and speed resulted in the highest mechanical properties and toughness. 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 the increased crystallinity. 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 instances such as for packaging applications. 

Summing up, 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 and potential use for packing applications. It was also shown that the processing technique presented can be a step forward for the large-scale production of bionanocomposites.

 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keyword [en]
Nanocomposite, Cellulose, Chitin, Extrusion, Polylactic acid
National Category
Composite Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-64863ISBN: 978-91-7583-929-5 (print)ISBN: 978-91-7583-930-1 (electronic)OAI: oai:DiVA.org:ltu-64863DiVA: diva2:1124446
Public defence
2017-09-15, E632, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-08-11 Created: 2017-07-13 Last updated: 2017-08-16Bibliographically approved
List of papers
1. 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 properties
Open this publication in new window or tab >>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 properties
2016 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 83, 89-97 p.Article in journal (Refereed) Published
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.

National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-7124 (URN)10.1016/j.compositesa.2015.05.024 (DOI)5711653a-fb96-48fd-a068-58adc0f9bfc6 (Local ID)5711653a-fb96-48fd-a068-58adc0f9bfc6 (Archive number)5711653a-fb96-48fd-a068-58adc0f9bfc6 (OAI)
Note

Validerad; 2016; Nivå 2; 20150604 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-07-13Bibliographically approved
2. Functionalized blown films of plasticized polylactic acid/chitin nanocomposite: Preparation and characterization
Open this publication in new window or tab >>Functionalized blown films of plasticized polylactic acid/chitin nanocomposite: Preparation and characterization
Show others...
2016 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 92, 846-852 p.Article in journal (Refereed) Published
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.

National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-10899 (URN)10.1016/j.matdes.2015.12.083 (DOI)9c73f46c-c3e5-4bd1-bdb2-e42bc9a9a2f3 (Local ID)9c73f46c-c3e5-4bd1-bdb2-e42bc9a9a2f3 (Archive number)9c73f46c-c3e5-4bd1-bdb2-e42bc9a9a2f3 (OAI)
Note
Validerad; 2016; Nivå 2; 20151218 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-07-13Bibliographically approved
3. Plasticized polylactic acid/cellulose nanocomposites prepared using melt-extrusion and liquid feeding: Mechanical, thermal and optical properties
Open this publication in new window or tab >>Plasticized polylactic acid/cellulose nanocomposites prepared using melt-extrusion and liquid feeding: Mechanical, thermal and optical properties
2015 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 106, 149-155 p.Article in journal (Refereed) Published
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.

National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-4891 (URN)10.1016/j.compscitech.2014.11.012 (DOI)2e4361c2-65ef-4231-bacc-e850b5eb33e7 (Local ID)2e4361c2-65ef-4231-bacc-e850b5eb33e7 (Archive number)2e4361c2-65ef-4231-bacc-e850b5eb33e7 (OAI)
Note
Validerad; 2015; Nivå 2; 20141002 (krioks)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-07-13Bibliographically approved
4. Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions
Open this publication in new window or tab >>Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions
(English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840Article in journal (Refereed) Submitted
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.

Keyword
Nanocomposites; Mechanical properties; Thermal properties; Microstructural analysis
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-64862 (URN)
Available from: 2017-07-13 Created: 2017-07-13 Last updated: 2017-07-13
5. Triethyl citrate (TEC) as a dispersing aid in polylactic acid/chitin nanocrystal nanocomposites prepared via liquid-assisted extrusion
Open this publication in new window or tab >>Triethyl citrate (TEC) as a dispersing aid in polylactic acid/chitin nanocrystal nanocomposites prepared via liquid-assisted extrusion
Show others...
(English)In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360Article in journal (Refereed) Submitted
Abstract [en]

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 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.

National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-64861 (URN)
Available from: 2017-07-13 Created: 2017-07-13 Last updated: 2017-08-15

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Herrera Vargas, Natalia
By organisation
Material Science
Composite Science and Engineering

Search outside of DiVA

GoogleGoogle Scholar

Total: 33 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf