Thesis
Investigation of poly(latic acid) (PLA)/sugar beet pulp bioplastics: processing, morphology, properties and foaming application
Washington State University
Master of Science (MS), Washington State University
2012
Handle:
https://hdl.handle.net/2376/100624
Abstract
Growing environmental problems and soaring petroleum prices have attracted intensive research interest in biopolymers. Among the commercially available options, poly(lactic acid)(PLA) exhibits excellent mechanical properties and is considered as the most promising alternative to petroleum-based polymers. However, its high price has limited adoption. In this study, sugar beet pulp (SBP), low-value residue after sugar extraction, was utilized and incorporated into PLA to reduce the cost while retaining biodegradability. PLA and SBP were compounded with a two-step processing method. SBP was first extruded in the presence of water and glycerol as plasticizers, thereby producing a thermoplastic SBP (TSBP), which can deform like a plastic component when melted. TSBP was then compounded with PLA and extruded into a sheet. A novel compatibilizer PBAT-g-MA was found to be effective in improving interfacial adhesion of the PLA and TSBP phases. A traditional compatibilizer PLA-g-MA was compared. Due to the flexible nature of PBAT which deterred early fracture between TSBP and PLA, composites with PBAT-g-MA exhibited better tensile properties than that compatibilized with PLA-g-MA. Improved crystallinity was also observed with PBAT-g-MA. A comparison of one-step and two-step processing methods were also developed. Results showed that the two-step processing method decreased particle size of the dispersed phase and produced better performance. Extrusion foaming the PLA/TSBP composite was also investigated. Chemical blowing agent (CBA) content, foaming temperature and rotational screw speed significantly affected morphology and properties of resulting foam samples. Due to the low melt strength of PLA/TSBP composite, excessive amounts of CBA content resulted in early escape of the blowing agent through interconnected TSBP particles. Foaming temperature interplayed with the pressure drop and affected nucleating rate. Results showed that very fine cell structure with high cell-population density is expected in low foaming temperature. Though fast rotational screw generated a high pressure drop, which is favorable for super saturation, a shear thinning effect occurred if it went too fast
Metrics
Details
- Title
- Investigation of poly(latic acid) (PLA)/sugar beet pulp bioplastics
- Creators
- Peng Zhan
- Contributors
- Jinwen Zhang (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Mechanical and Materials Engineering, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525073901842
- Language
- English
- Resource Type
- Thesis