Mechanical performance of cellulose multilayer laminate and cellulose nanocrystal nanocomposite

Jen-Chieh Liu, Purdue University

Abstract

Cellulose nanomaterials (CNs) have become attractive materials in recent years as a result of renewed interests from consumers, industry and governments to use renewable/sustainable, carbon neutral, and non-petroleum based materials. CNs have been considered as a reinforcement phase in polymer composites, protective coatings, barrier/filter membrane systems, network structures for tissue engineering and substrates for flexible electronics because of good mechanical properties, low density, low thermal expansion and surfaces that can be readily chemically functionalized. Two types of CNs extracted from wood (cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC)) were used in multilayer laminates and polyurethane nanocomposite. Neat CNF films were boned on the wood flake or adhered with polymer interlayer to fabricate CNF-WF laminate and CNF-polymer multilayer laminate. Similarly, high quality CNC films were also prepared to stack with polymer to fabricate CNC-polymer multilayer laminate. Moreover, the freeze-dried CNCs used as reinforced nanofiller were re-dispersed in the thermoplastic polyurethane to fabricate polymer nanocomposite. Homogeneous and transparent CNF films fabricated from (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) based CNF suspension were adhered on the wood flake (WF) to form CNF-WF laminate with phenol-formaldehyde resin via a lamination process. The mechanical properties of CNF-WF laminate had improved as compared to the neat WF, especially in the transverse direction, because of the anisotropic properties of WF. Linear polystyrene-poly(ethylene/butylenes)-polystyrene (SEBS) triblock copolymer and polyvinyl butyral (PVB resin) were also adhered with CNF films to fabricate CNF-polymer multilayer laminates. Though the mechanical performance of the laminates was reduced by incorporating the polymer interlayer, the toughness (work of fracture) of the laminates was improved because polymer interlayer can dissipate more energy when breaking the laminates. CNC-polymer multilayer laminates were also prepared with PVB and SEBS interlayer via lamination process. In the CNC laminate system, all the properties of the laminates with different polymer volume fraction were reduced. However, an attractive result was observed in the CNC-maleated SEBS laminate with high polymer volume fraction. In testing, the maleated SEBS laminate presented multiple breaking steps and large elongation, which would suggest that the maleated SEBS interlayer can stop crack propagation throughout the entire laminate and can dissipate more energy during failure. Except for fabricating CNF and CNC laminates, freeze-dried CNCs were also re-dispersed in thermoplastic polyurethane (TPU) to fabricate CNC reinforced nanocomposites. The elastic modulus and thermal stability of the nanocomposite were improved with increasing CNC content in the TPU matrix. The improved properties were due to the formation of hydrogen bonding between CNCs and TPU matrix. Moreover, the ductility (strain of failure) of the nanocomposite was similar to pure TPU which would suggest that CNCs only hindered the mobility of hard domains, but had no influence on the chain movement of soft domains in nanocomposites.

Degree

Ph.D.

Advisors

Moon, Purdue University.

Subject Area

Materials science

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