Grafted α-cellulose-poly(hydroxybutyrate-co-hydroxyvalerate) Biocomposites Liqing Wei and Armando G. McDonald Renewable Materials Program June 2015
1.1 Why Use Bioplastics Issues with Conventional Plastic >300 million tons of plastics are produced annually >40 % of these conventional plastics are used in short-term applications Environmental pollution both terrestrial & marine How to overcome these issues Need to introduce bioplastics from renewable resources into the market with comparable or improved properties Biodegradable
1.2 Bacterial polyhydroxyalkanoates Carbon Cycle of PHA PHA granules PHA R PHB - CH 3 PHV -CH 2 CH 3 PHBV - CH 3 & CH 2 CH 3 PHHp -(CH 2 ) 3 CH 3 PHBO -CH 3 & -(CH 2 ) 4 CH 3 HB: 3-hydroxybutyrate; HV: 3-hydroxyvalerate H O R x O OH n PHA general structure R = C 1 -C 13 x = 1 to 3 or more
Packaging films: Shopping bags, containers & paper coatings, single-use items Biomedical implant materials: Sutures, suture fasteners, meniscus repair devices, rivets, tacks, staples Limitations 1.3 Applications of PHA PHA s poor melt strength limits processing & product options en.european-bioplastics.org http://www.biomasspackaging.com/e ducation/bioplastics www.multimedgrm.sld.cu
1.4 Biocomposites Both reinforcement (e.g., wood & cellulose) & matrix (PLA, PHA, starch) from renewable sources Fiber reinforcement improves performance Work required to improve compatability & properties
1.5 Summary of bioplastics BIOPLASTICS (e.g., PHB/PLA) ADVANTAGES SHORTCOMINGS Excellent biodegradability Environmentally-friendly synthesis Brittleness (PHB) Narrow processing window From renewable resource Thermal degradation Good biocompatibility Poor interaction with natural fibers Good compostability Relatively higher prices How to over come the shortcomings of bioplastics?
2. Objectives 1. Produce α-cellulose fibers from small diameter lodgepole pine 2. Prepare α-cellulose-graft-phbv biocomposites via the grafting onto strategy during in-situ reactive extrusion 3. Evaluation of α-cellulose-graft-phbv biocomposite materials
3. Grafting approach Enhance the interphase between α-cellulose & PHBV by grafting Grafting by reactive processing with peroxide radicals initiation PHBV
3.1 Experimental: α-cellulose Isolation Lodgepole pine logs Lodgepole Pine wood fibers Acetone Extractive free fibers Wiley milled <1 mm Delignification NaClO 2 @70 o C Ф <10 cm Aspect ratio = 29, L = 0.5 mm Holocellulose 17.5% NaOH α-cellulose 96% purity
3.2 Experimental: grafting Processing: 175 o C using Dynisco mixing molder-extruder α-cellulose; PHBV (22 mol% HV, Tianan Biopolymer) Reactive extrusion: DCP (2%), reaction time (10 min) Controls - PHBV & α-cellulose/phbv (αcell-phbv) blend Rheometry Bohlin CVO-100 Molded specimens
1 PHBV G' T=175 C Cell-PHB G' Cell-g-PHB G' 4.1 Results: Rheometry (a) 0.1 0.1 0.1 1 10 100 (rad/s) 1 10000 G c = 4600 Pa 10000 G c = 970 Pa G'' (Pa) 1000 100 T=170 C G c = 574 Pa PHBV G'' Cell-PHBV G'' Cell-g-PHBV G'' PHBV G' Cell-PHBV G' Cell-g-PHBV G' 1000 100 G' (Pa) (b) 0.1 1 10 100 (rad/s) Melt viscosity increased due to grafting & crosslinking
4.2 Results: morphology Melt blended α-cellulose -PHBV α-cellulose-graft-phbv
Stress, σ (MPa) 4.3 Results: tensile properties 18 15.9MPa, 18.8% 15 12 αcell-g-phbv 13.9MPa 14.4% 11.8Mpa 19.8% 9 αcell-phbv PHBV 6 3 0 0 5 10 15 20 25 Strain, ε (%)
Storage modulus, E (MPa) 4.4 Results: Viscoelastic properties 1600 1200 αcell-g-phbv A 30 C Interfacial adhesion factor Samples Tanδ 30 C V f (%) A 30 C 800 400 0 αcell-phbv PHBV 25 50 75 100 125 150 Temperature ( o C) Neat PHBV 0.090 0 - αcell-phbv 0.065 58 0.72 αcell-g-phbv 0.050 58 0.32 A = (1/(1-V f )) (tan δ c /tan δ m ) 1 Lower A better adhesion
Crystallinity 4.5 Results: FTIR spectroscopy Cellulose total crystallinity index TCI = A 1370 /A 2900 PHBV crystallinity I PHBV/C=O = A 1720 /A 1740 3.0 2.5 2.0 Cell PHBV 1.5 1.0 0.5 0.0 αcell PHBV αcell-phbv αcell-g-phbv DSC analysis showed similar trends for PHBV crystallinity
Crystallite size (Å) Crystallinity index 4.7 Results: XRD Crystallinity indicies: CrI αcell = 1 (I am /I 002 ) CrI PHBV = I 17 /I total Crystal size D hkl = K x λ / (β 1/2 x cosɵ) 250 200 Cellulose PHBV 0.6 0.5 Cellulose PHBV 150 100 0.4 0.3 0.2 50 0.1 0 αcell PHBV αcell-phbv αcell-g-phbv 0 αcell PHBV αcell-phbv αcell-g-phbv
Weight (%) 4.8 Results: Thermal stability 100 80 αcell-g-phbv 60 40 αcell-phbv αcell 20 PHBV 0 50 150 250 350 450 550 Temperature ( o C)
5. Conclusions Successfully made α-cellulose-g-phbv by reactive extrusion Melt viscosity (elasticity) increased by grafting Observed good interfacial bonding/compatibility between cellulose & PHBV Crystallinity and crystal size decreased for PHB & cellulose as a result of grafting The α-cellulose-g-phbv was more thermally stable & improved tensile properties than simple composite blend In-situ reactive extrusion is a practical approach for improving biocomposite performance
Thank you! Questions? Acknowledgements: Financial support from Grant number 08-JV-11111133-036.