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Strategies for Utilizing Biobased and Recycled Resources for Polylactide Plasticization
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There are many aspects that should be considered to achieve truly "environmental friendly" and "sustainable" materials. These include the raw material resource, the energy consumption, the chemicals generated and used, the emissions during production, processing, transportation, disposal and so on. The work presented in this thesis focused on development of strategies for valorization of biopolymers and further utilization of the derived chemicals for plasticization of polylactide (PLA). This would retain the material value of the biopolymers, the degradability and biobased nature of PLA, while simultaneously broadening the application areas and properties of PLA.

Two green, and efficient methodologies for chemical recycling of poly(3-hydroxybutyrate) (PHB), a natural biodegradable biopolymer produced in microorganisms as an energy storage material, were demonstrated. Full degradation to monomeric degradation products: crotonic acid (CA), 3-hydroxybutanoic acid (3HB) and 3-methoxybutanoic acid (3MB) was obtained in only 20 minutes through microwave assisted degradation in green solvents. Degradation parameters, such as solvent and basicity, were carefully evaluated for achieving high yield and fast degradation and the constituent ratio of degradation products could be tuned by adjusting the degradation time under the optimized condition. Meanwhile PHB oligomers with crotonic end groups (dPHB) were formed by thermal degradation of PHB during extrusion, which is an industrially viable process. The effects of degradation temperature and degradation time on the formation of degradation products were carefully adjusted, and the degradation kinetics at different temperatures were evaluated. Glucose, a depolymerization product of cellulose and starch, was modified by hexanoic acid to star shaped glucose esters (GHx) with different varying degrees of substitution by adjusting the reaction time.

Two methodologies to plasticize PLA by utilizing the products from PHB recycling or the synthesized glucose esters were evaluated aiming at plasticizers with enhanced migration resistance compared to the physical blends or commercial analogues: 1) anchoring linear oligomeric plasticizers onto PLA and 2) blending low molar mass star shaped molecules into the PLA matrix. Specifically, PLA-CA-PBSA was prepared by coupling poly(butylene succinate-co-adipate) (PBSA) to CA functionalized PLA, PLA-g-dPHB was obtained by coupling dPHB onto the PLA main chain via reactive extrusion. PLA blends with star shaped GHx were also prepared. Decrease of Tg was observed for all the plasticized PLA samples. Blending GHx reduced the Tg of PLA by about 30 ºC and a decrease in Tg for approximately 25 ºC and 20 ºC was realized by coupling PLA with dPHB or PBSA, respectively. All plasticized PLA materials showed increased elongation at break. For PLA-g-dPHB a 66-fold increased elongation at break was achieved. The crystallization capacity of both PBSA and dPHB coupled PLA was improved at the same times as the PLA was plasticized. This is explained by the grafting points acting as nucleating sites and is further facilitated by the improved chain mobility of the PLA chains.

The proposed approaches for PHB recycling, modification of glucose and the coupling or blending strategies demonstrated great promise for the concept of utilizing recycled biopolymers/biomass for plasticization of PLA.

Abstract [sv]

Det finns många aspekter som bör beaktas för att uppnå verkligt "miljövänliga" och "hållbara" material. Dessa inkluderar typen av råvaruresurser, den energi som förbrukas vid framställningen, alla de kemikalier som genereras och används, utsläppen under produktion, bearbetning, transporter, avfallshantering och så vidare. Arbetet som presenteras i denna avhandling fokuserade på utvecklingen av strategier för valorisering av biopolymerer och användning av de framtagna kemikalierna för mjukgöring av polylaktid (PLA). Detta angreppsätt behöll materialvärdet av biopolymererna och den nedbrytbara och biobaserade naturen av PLA, samtidigt som egenskaper och framtida applikationsområden hos PLA kunde breddas.

Två gröna och effektiva metoder för kemisk återvinning av poly(3-hydroxibutyrat) (PHB), en naturlig bionedbrytbar biopolymer som produceras i mikroorganismer som energilagringsmaterial, demonstrerades. Fullständig nedbrytning till monomera nedbrytningsprodukterna: krotonsyra (CA), 3-hydroxibutansyra (3HB) och 3-metoxibutansyra (3MB) erhölls inom 20 minuter vid mikrovågsugnsassisterad nedbrytning i gröna lösningsmedel. Nedbrytningsparametrar såsom lösningsmedel och basicitet utvärderades grundligt för att uppnå högt utbyte och snabb nedbrytning, och sammansättningen av nedbrytningsprodukterna kunde kontrolleras genom nedbrytningstiden under de optimerade förhållandena. PHB oligomerer med ändgrupper av krotonsyra (dPHB) bildades genom termisk nedbrytning av PHB vid extrudering, vilket är en industriellt gångbar process. Effekterna av nedbrytningstemperatur och tid på framställningen av nedbrytningsprodukterna justerades noggrant och nedbrytningskinetiken utvärderades vid olika temperaturer. Glukos, en depolymerisationsprodukt av cellulosa och stärkelse, modifierades med hexansyra till stjärnformade glukosestrar (GHx) med olika substitutionsgrader genom justering av reaktionstiden.

Två metoder för att mjukgöra PLA utvärderades genom att återvinningsprodukterna från PHB eller de syntetiserade glukosestrar användes, med avsikt att åstadkomma mjukgörare med förbättrat migrationsmotstånd jämfört med fysiska blandningar eller kommersiella analoger: 1) kovalent ympning av linjära oligomera mjukgörare på PLA och 2) blandning av stjärnformade molekyler med låg molmassa i PLA-matrisen. Mer precist, PLA-CA-PBSA framställdes genom att koppla poly(butylen succinat-sam-adipat) (PBSA) till CA-funktionaliserad PLA, och PLA-g-dPHB erhölls genom koppling av dPHB på PLA-huvudkedjan via reaktiv extrudering. PLA-blandningar med stjärnformade GHx framställdes också. En minskning av glasomvandlingstemperaturen, Tg, observerades för alla PLA-proverna som innehöll mjukgörare. Blandning med GHx reducerade Tg för PLA med cirka 30 °C och en minskning i Tg med cirka 25 °C och 20 °C nåddes när dPHB eller PBSA kopplades på PLA-huvudkedjan. Alla PLA-material som innehöll mjukgörare visade en ökad brottöjning, där PLA-g-dPHB uppnådde en 66-faldigt ökad brottöjning. Kristallisationskapaciteten för både PBSA- och dPHB-ympad PLA förbättrades samtidigt som PLA mjukgjordes. Detta förklaras av ympningspunkterna som fungerade som kärnbildningspunkter samt av att kristallisation underlättades ytterligare av en lägre Tg, vilken leder till en ökad kedjerörlighet hos PLA-kedjor.

De utvecklade metoderna för PHB-återvinning, modifiering av glukos och kopplings- eller blandningsstrategierna visade sig vara koncept som är lovande för nyttjandet av återvunna biopolymerer/biomassa för tillverkning av mjukgjord PLA.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2016.
Series
TRITA-CHE-Report, ISSN 1654-1081
Keyword [en]
Polylactide, poly(3-hydroxybutyrate), poly(butylene succinate-co-adipate), bio-based, microwave, reactive extrusion, recycling, plasticizing, migration resistance, crystallization
Keyword [sv]
polylaktid, poly(3-hydroxibutyrat), poly(butylen succinat-sam-adipat), biobaserade, mikrovågsugn, reaktiv extrudering, återvinning, mjukgörare, migrationsmotstånd, kristallisering
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-190948ISBN: 978-91-7729-068-1OAI: oai:DiVA.org:kth-190948DiVA: diva2:953842
Public defence
2016-09-16, Kollegiesalen, Brinellvägen 8, Stockholm, 13:30 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 311815
Note

QC 20160825

Available from: 2016-08-25 Created: 2016-08-18 Last updated: 2016-08-25Bibliographically approved
List of papers
1. Microwave-Assisted Reaction in Green Solvents Recycles PHB to Functional Chemicals
Open this publication in new window or tab >>Microwave-Assisted Reaction in Green Solvents Recycles PHB to Functional Chemicals
2014 (English)In: ACS Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 2, no 9, 2198-2203 p.Article in journal (Refereed) Published
Abstract [en]

An efficient microwave-assisted process for chemical recycling of poly(3-hydroxybutyrate) (PHB) in green solvents was demonstrated. Previously, PHB has been thermally recycled to crotonic acid and unsaturated oligomers. Our aim was to utilize green solvents (water, methanol, and ethanol) under alkaline conditions to achieve fast hydrolysis and monomeric or oligomeric degradation products with carboxyl and hydroxyl or methoxy or ethoxy end groups. Preliminary screening confirmed that the most efficient degradation process was obtained in alkaline methanol. In addition, sample amount, sodium hydroxide concentration, and degradation time all influenced the degradation process and final degree of degradation. Comparison with pure thermal degradation clearly demonstrated the effectiveness of the microwave-assisted process as the time and temperature needed for complete degradation was significantly reduced. Several characterization techniques were utilized for mapping the degradation processes and resulting degradation products. After optimization of the process, complete degradation of PHB to monomeric degradation products (3-hydroxybutanoic acid, 3-methoxybutanoic acid, and crotonic acid) was reached after only 20 min of microwave heating at 110 degrees C. Functional chemicals for synthesis or modification of biopolymers are thus obtainable from microwave-assisted degradation of PHB in green solvents. This offers new possibilities for retaining the material value of PHB via chemical recycling.

Keyword
Hydrolysis, Microwave, Poly(3-hydroxybutyrate), Polyester, Recycling
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-152563 (URN)10.1021/sc500397h (DOI)000341229100015 ()2-s2.0-84906877348 (ScopusID)
Funder
EU, FP7, Seventh Framework Programme, 311815
Note

QC 20140929

Available from: 2014-09-29 Created: 2014-09-29 Last updated: 2016-08-25Bibliographically approved
2. Poly(lactide)-g-poly(butylene succinate-co-adipate) with High Crystallization Capacity and Migration Resistance
Open this publication in new window or tab >>Poly(lactide)-g-poly(butylene succinate-co-adipate) with High Crystallization Capacity and Migration Resistance
2016 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 9, no 5, 313Article in journal (Refereed) Published
Abstract [en]

Plasticized polylactide (PLA) with increased crystallization ability and prolonged life-span in practical applications due to the minimal plasticizer migration was prepared. Branched plasticized PLA was successfully obtained by coupling poly(butylene succinate-co-adipate) (PBSA) to crotonic acid (CA) functionalized PLA. The plasticization behavior of PBSA coupled PLA (PLA-CA-PBSA) and its counterpart PBSA blended PLA (PLA/PBSA) were fully elucidated. For both PLA-CA-PBSA and PLA/PBSA, a decrease of Tg to around room temperature and an increase in the elongation at break of PLA from 14% to 165% and 460%, respectively, were determined. The crystallinity was increased from 2.1% to 8.4% for PLA/PBSA and even more, to 10.6%, for PLA-CA-PBSA. Due to the inherent poor miscibility between the PBSA and PLA, phase separation occurred in the blend, while PLA-CA-PBSA showed no phase separation which, together with the higher crystallinity, led to better oxygen barrier properties compared to neat PLA and PLA/PBSA. A higher resistance to migration during hydrolytic degradation for the PLA-CA-PBSA compared to the PLA/PBSA indicated that the plasticization effect of PBSA in the coupled material would be retained for a longer time period.

Place, publisher, year, edition, pages
MDPI AG, 2016
Keyword
polylactide, poly(butylene succinate-co-adipate), plasticizing, crystallization, oxygen permeability, migration resistance
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-189952 (URN)10.3390/ma9050313 (DOI)000378628500008 ()2-s2.0-84969931582 (ScopusID)
Note

QC 20160727

Available from: 2016-07-27 Created: 2016-07-25 Last updated: 2016-08-25Bibliographically approved
3. Two step extrusion process: From thermal recycling of PHB to plasticized PLA by reactive extrusion grafting of PHB degradation products onto PLA chains
Open this publication in new window or tab >>Two step extrusion process: From thermal recycling of PHB to plasticized PLA by reactive extrusion grafting of PHB degradation products onto PLA chains
Show others...
2015 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 48, no 8, 2509-2518 p.Article in journal (Refereed) Published
Abstract [en]

A green and industrially viable two-step process was demonstrated for toughening polylactide (PLA) without compromising the biobased and biodegradable nature. First, poly(3-hydroxybutyrate) (PHB) biopolymer was thermally degraded in an extruder to create PHB oligomers (dPHB) with functional end-groups suitable for further reactions. Second, a reactive extrusion process was developed to covalently anchor dPHB onto the main chain of PLA. PLA with 20% (w/w) grafted dPHB demonstrated an impressive elongation at break of 538%, 66 times higher than that of pure PLA and significantly higher than the elongation at break of the corresponding physical blend. At the same time WAXD measurements illustrated that grafting significantly increased the crystallization ability of PLA. We present a viable recycling route for PHB and a highly promising approach for fully biobased toughened PLA with covalently anchored PHB plasticizers.

Keyword
Chains, Degradation, Grafting (chemical), Recycling, Solvents, Degradation products, Elongation at break, Extrusion process, Functional end groups, Poly(3-hydroxybutyrate), Reactive extrusion process, Reactive extrusions, Thermal recycling, Extrusion
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-167742 (URN)10.1021/acs.macromol.5b00235 (DOI)000353864800020 ()2-s2.0-84928661327 (ScopusID)
Funder
EU, FP7, Seventh Framework Programme, 311815
Note

 QC 20150601

Available from: 2015-06-01 Created: 2015-05-22 Last updated: 2016-08-25Bibliographically approved
4. Migration resistant glucose esters as bioplasticizers for polylactide
Open this publication in new window or tab >>Migration resistant glucose esters as bioplasticizers for polylactide
2015 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 132, no 18, 41928Article in journal (Refereed) Published
Abstract [en]

Environmental and sustainability issues have catalyzed efforts to replace traditional polymer additives with biobased alternatives. Glucose pentaacetate (GPA) and sucrose octaacetate (SOA) as model commercial saccharide esters and three synthesized glucose hexanoate esters (GHs) were evaluated as bioplasticizers for polylactide (PLA). For the GHs different reaction times were utilized to reach plasticizers with different number of hexanoate groups to establish how the degree of substitution influences miscibility and migration resistance of the plasticizers. The synthesized GHs, GPA, and SOA all showed good miscibility with PLA. Largest improvements in strain at break were observed for the PLA films containing GH plasticizers. These films also exhibited simultaneous increase in stress at break as compared to plain PLA. The GH plasticizers had low tendency to migrate during aging in water and this migration resistance increased with increasing degree of substitution. The GHs are, thus, promising plasticizer alternatives for bioplastics as they also retain the biodegradable nature of these biobased materials.

Keyword
biodegradable, biopolymers and renewable polymers, blends, plasticizer, polyesters
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-161941 (URN)10.1002/app.41928 (DOI)000349390100021 ()2-s2.0-84922728934 (ScopusID)
Funder
Swedish Research Council, 2012-4369
Note

QC 20150408

Available from: 2015-04-08 Created: 2015-03-20 Last updated: 2016-08-25Bibliographically approved

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