Rheological Design of Sustainable Block Copolymers Alex Mannion - PowerPoint PPT Presentation

Rheological Design of Sustainable Block Copolymers Alex Mannion Advisors: Frank Bates, Chris Macosko Final Oral Examination Augsut 4 th , 2016

Safety moment: proper hand washing jst.umn.edu 2

Rheological design Biological systems Paint Cosmetics Food 3

Block copolymers Morphology AB diblock copolymer Dalsin, S. J.; Bottlebrush Polymers: Synthesis, Rheology, and Self-Assembly , 2016 Architecture “The rheological behavior of block copolymers is perhaps the least ABA triblock copolymer AB diblock copolymer understood of all categories of complex fluids…” – Professor Ron Larson, Dept. of Chemical Engineering, U. of Michigan 1 ABABA… multiblock copolymer 4 1. “Structure and Rheology of Complex Fluids,” Oxford University Press, Ronald G. Larson, 1999.

Sustainability Past… Future… 5 Ellen MacArthuer Foundation, “The New Plastics Economy: Rethinking the Future of Plastics,” 2016

Thesis Outline Chewing Gum Branched Multiblock Copolymers Practical Materials Chapter 2 Chapter 4 Chapter 6 o o + o o o o o o Chapter 3 Chapter 5 Chapter 7 o + o 6

Next generation chewing gum Goal: • Replace conventional chewing gum ingredients with new materials to simplify formulation • Maintains the same sensory profile Morgret, L., Science-Based Design of High Performance Bubblegum , 2005 What is chewing gum’s rheological fingerprint? 7

Gum materials Chewing gums Bubble gums Sample preparation Mouth chewing Important deformation regimes 1 • shear strains: 10-1000% • shear rates: 10-100 s -1 • shear stresses: >10 4 Pa Ralph DeLong, UMN, Dentistry 8 1. Anderson et al., J. Oral Rehabil. , 2002 ; Steffe J., Rheological Methods in Food Processing Engineering , 1992

Linear viscoelasticity (LVE): oscillatory shear Critical gel equations 1 S : stiffness n : strength of gel network Rouse model equations Fitting parameters S (Pa-s n ) S (Pa-s n ) n n G R (Pa) (s) 30100 30100 0.228 0.228 24300 0.0440 9 1. Chambon et al., J. Rheol, 1987

Start up of steady uniaxial extension Uniaxial Chewing gums Bubble gums extension: L 0 L Constant Hencky strain rate: Transient extensional viscosity: Large strains at break ( > 4.0) correlate with desirable sensory feel Larger stresses at break for bubble gums  stabilizes bubble blowing 10

Block copolymer blends for chewing gum applications Why use block copolymers? What is chewing gum’s rheological fingerprint? Microphase separate  tunable solids • • Precise control over molecular architecture ABA triblock AB diblock Fragile critical gel fluid with high extensibility Glass Goal: Next generation chewing gum + Rubber Block copolymers Softener, “critical gel” High extensibility behavior 11

ABA triblock/AB diblock blends: extension M n (kg/mol) w PLA M n (kg/mol) w PLA AB 7.4 0.41 AB 7.4 0.41 ABA ABA 95.1 0.36 A = poly(D,L-lactide) B = poly(cis-1,4-isoprene) 12 Lee, S. Structure and Dynamics of Block Copolymer Based Soft Materials , 2011

Three component system Synthesis A B ε -decalactone dimethanol A B A benzene Sn(Oct) 2 130 °C, 12 h A B Benzyl alcohol Sn(Oct) 2 Investigated effects of toluene 110 °C, 4 h • Polymer composition D,L-lactide • Molecular weight Advantages : Poly(D,L-lactide) (L) Poly( ε -decalactone) (D) • High conversion, well-controlled Glassy, T g ≈ 50 °C Rubbery, T g ≈ -50 °C • Scalable • Renewable/FDA approved materials 13

Synthesized polymers Targeted a range of PLA weight fractions for three sets of polymers: Đ # * Sample M n f PLA Three polymer species [kg mol -1 ] DL-S1 5.6 0.15 1.11 DL-S2 8.0 0.33 1.13 D L DL-S3 9.0 0.41 1.18 DL-M1 32 0.09 1.05 Produced 24 blends 80% diblock DL-M2 38 0.21 1.06 L D 20% triblock DL-M3 46 0.32 1.06 LDL-1 102 0.05 1.07 LDL-2 112 0.11 1.09 L D L LDL-3 133 0.23 1.06 *calculated from end-group analysis of 1 H-NMR # determined from room-temperature size-exclusion chromatography (SEC) † determined from differential scanning calorimetry (DSC) 15

Effect of triblock composition 80 wt.% 20 wt.% + Vary PLA weight D L fraction L D L (DL-S2) (LDL-1, LDL-2, or LDL-3) 15

Effect of diblock molecular weight 80 wt.% 20 wt.% Small angle X-ray scattering : + D L L D L D L (DL-S2) (DL-M2) Vary diblock ratio (2:0, 1:1, or 0:2) Exact morphology does not matter! 16

Blends for chewing and bubble gums Key rheological parameters: Best blends: Polymer LDL-2 L D L …with short DL diblocks D L Future work • Increase strain at break with multiblock architecture 17

Thesis Outline Chewing Gum Branched Multiblock Copolymers Practical Materials Chapter 2 Chapter 4 Chapter 6 o o + o o o o o o Chapter 3 Chapter 5 Chapter 7 o + o 18

Blown film extrusion Goals: • Stable bubble • Controlled thickness • Fast through-put Extensional viscosity high at high rates Rheological targets: Shear viscosity low at high rates 19

One commercial success story: poly(lactide) (PLA) sugar lactic acid lactide polylactide catalyst - H 2 O Applications Properties • ~$1 per lb • Mechanically similar to polystyrene • Compost 100% in ~45 days Natureworks.com 20

Deficiencies of commercial PLA Poor mechanical properties Poor melt strength Extensional rheology Tensile testing Machine direction (MD) Blown film extrusion MD TD Transverse direction (TD) 21

Toughening PLA with multiblock architecture loop Elastomeric block dangling ends Poly( D,L -lactide) T g << 25 °C T g ≈ 50 °C • Effectively toughens PLA 1 2 • Accessible T ODT bridge Panthani et al, Macromolecules, 2015 Bridging domains act as reinforcements n greater toughness More bridges per molecule, the tougher the material 22 1. Panthani et al, Macromolecules, 2013 2. Wu et al., Macromolecules , 2005

Tuning processability with long chain branching Strategy Long chain branching can lead to strain hardening 1 o couple o x Linear triblock Linear multiblock x Long chain branch LDL (DL) n o o o o couple o x o o x o Branched multiblock Star diblock (DL-4) n DL-4 Short branch Versatile and robust platform: 1) Polymer composition 2) Block lengths (~ M c ) 3) Accessible T ODT 23 1. Meissner et al . , J. Appl. Polym. Science, 1972

Synthesis and characterization Size exclusion chromatography (SEC) Synthesis Linear Branched ε -decalactone dimethanol benzene Sn(Oct) 2 130 °C, 12 h Sn(Oct) 2 pentaerythritol toluene 110 °C, 4 h D,L-lactide <n> = number of subunits in final multiblock Đ † * Sample M W <n> f PLA toluene [kg/mol] $ pyridine LDL linear triblock 18.4 -- 0.72 1.14 25 °C, 2 h sebacoyl chloride DL-4 star diblock 39.7 -- 0.73 1.10 (DL) n linear multiblock 159 5.6 0.72 1.92 (DL-4) n branched multiblock 151 2.3 0.73 2.00 *calculated from 1 H-NMR end group analysis $ determined with SEC in room temp THF with a † determined with SEC in room temp THF with a RI detector MALS detector 24

Estimating branching from SEC with multi-angle light scattering (MALS) Linear chain: g = 1 Contraction factor: 4-arm star: g = 0.63 SEC-MALS Hyperbranched “Comb-like” High molecular weight species resemble a comb polymer 25

Key advantages of branched multiblock Extensional rheology Tensile testing (DL) n linear multiblock (DL-4) n branched multiblock Multiblocks have increased Strain hardening due to branching toughness 26

Key limitation: gelation A f + B g Too much coupling agent… Gel point equation: couple Values of <n> at gel point: g E 2 3 4 5 f E ∞ 2 3.0 2.0 1.7 3 4.0 2.0 1.6 1.4 4 3.0 1.8 1.5 1.4 5 2.7 1.7 1.4 1.3 … leads to a gel 27

New approach: A 2 + B 2 /B 3 Approach SEC o + B 2 o A 2 Amount of B 3 PLA diol, B 3 19 kg mol -1 Theory Coupling Branching 28

Estimating branching from SEC with multi-angle light scattering (MALS) SEC-MALS High molecular weight species becoming increasingly branched 29

Extensional behavior Extensional rheology Temperature: 120 °C bPLA-90 bPLA-80 bPLA-50 bPLA-95 Amount of B 3 30

Outlook Approach B 2 o o + o o A 2 B 3 With A 2 + B 2 /B 3 reaction, can easily tune: Easily adoptable to • Coupling extent ( <n> ) triblock copolymers • Amount of branching • Viscosity Applicable to reactive extrusion 31

Thesis Outline Chewing Gum Branched Multiblock Copolymers Practical Materials Chapter 2 Chapter 4 Chapter 6 o o + o o o o o o Chapter 3 Chapter 5 Chapter 7 o + o 32

Acknowledgements Collaborators Funding Collaborators L.E. and D.H. Scriven Fellowship Branched Multiblock Polymers Chewing Gum • Dr. David Giles • Prof. Marc Hillmyer • Dr. Debbie Schneiderman • Prof. Sangwoo Lee • Matt Irwin • Prof. Randy Ewoldt • Maxwell Nagarajan • Dr. Luca Martinetti • Dr. Mark Martello Pressure Sensitive Adhesives • Dr. Debbie Schneiderman • Dr. Tessie Panthani • David Giacomin • McKenzie Coughlin • Renxuan Xie Facilities • Joel Updyke • Willy Voje • Minnesota Characterization Facility • Tao Yang Blown Film Extrusion • Polymer Characterization Facility • Les Morgret • Dr. Mike Manno • Hillmyer Group • Rafael Bras • Tuoqi Li • Niku Tseng • Liangliang Gu • Jacob Wright • Joseph Schaefer 33