Graded Architecture Composites Amy Huang – Newton North High School Akhil Meka – Chelmsford High School Professor Marilyn Minus Graded Architecture Composites

Background Semicrystalline matrix comprised of spherulites Lamellar crystals Composite material Hybrid particles with lamellae (confined) Amy Explain: spherulites; CNTs have been shown to induce crystallization; CNTs are ONLY being used to induce crystallization; looking for a film with high toughness (modulus, strength, and elongation) Alumina platelet Alumina with CNT crystal seeds Materials Science and Engineering, William D. Callister Jr, Wiley Schematic courtesy of Jessica Faust

Materials Polypropylene (MW = ~250,000 g/mol) dissolved in Xylene at 140 °C Hybrid particles (Alumina platelets and single-walled carbon nanotubes) in Dimethyl formamide at varying temperatures Akhil

Our Focus This study is aimed at understanding the appropriate solution crystallization conditions under different rates of cooling for the solvent in order to optimize the growth of polypropylene crystals on hybrid particles in a graded composite. Akhil

Actual representation of powder after filtering Processing Syringe Actual representation of powder after filtering Beaker Hot Plate Amy Explain: run through step-by-step; spherulites in film Ignore: solvent/solvent problems ****ADD LABELS

Processing Uniform Dispersion Melt Film Mechanical Testing Hot Plate, T = 180°C Glass Slide PP Film Heavy Preheated Steel Plate Film is heated to 180°C for 1min 30sec and pressed into a thin film Mechanical Testing Uniform Dispersion Amy Explain: run through step-by-step; less spherulites Melt the spherulites, but reformed Take powder picture and show them Actual representation of film after melting

Temperature Profiles Undercooling/ΔT Akhil

Alumina Particle Solution Temperature DSC and X-Ray Results Alumina Particle Solution Temperature (°C) Tm (°C) 𝝙H (J/g) (ΔH*PP = 207 J/g) XC, DSC (%) 6-65 165.4-168.0 96-131.7 47.3-63.6 Akhil Differential Scanning Calorimetry ***1 ROW USE RANGES (BOX AROUND ENTHALPY AND %), BOX CRYSTALLINITY IN XRAY, TEXT BOX ABOUT CONFINED (XC DSC- XC XRD), SCHEMATIC ABOUT CONFINED CRYSTAL Lamellae Crystallization=XC, XRD-XC, DSC

Mechanical Testing Mechanical testing performed by an Instron machine Amy Transition: After confirming that the crystals we wanted were there… Explain: performed mechanical testing on an Instron machine at 10mm/min

Alumina Particle Solution Temperature Mechanical Testing Alumina Particle Solution Temperature (°C) Modulus, E (MPa) Tensile Stress, σ (i.e., Strength) Elongation, ε (%) 6 778.9 ± 46.7 29.9 ± 0.8 1055.4 ± 746.3 20.1 746.3 ± 34.6 27.5 ± 0.1 63.1 ± 51.9 38.3 664.1 ± 39 27.6 ± 4.9 511.3 ± 479.9 41.3 955.5 ± 130.8 34.1 ± 2.4 85.1 ± 67 45.5 811.7 31.14 24.8 (only one sample tested) 51.2 895 ± 30.9 35.3 ± 0.7 36.9 ± 17.1 scratches bubbles Amy Explain: interest is primarily in the modulus and the yield strength; there is a significant increase in modulus; however, there are no consistent trends in the yield strength due to processing inconsistencies; some elongation indicates that the material retains high ductility

Mechanical Testing Most samples had similar degrees of undercooling The area with the same degree of undercooling exhibits a trend in the elastic modulus Trend is associated with the cooling rate Amy Explain: difference between rate and undercooling

Key Results DSC crystallinity values, based on crystal melting, showed similar results regardless of crystallization conditions. Greater crystallinity measured by X-ray analysis as compared to DSC confirms that confined crystals exist in the samples, which is consistent with the interphase morphology. Slower cooling rates were associated with higher particle injection temperatures. Defects present during film melt-processing procedures limit strength and elongation trends in the films. Akhil

Conclusion This study shows the impact of solution crystallization conditions on the formation of interphase polypropylene crystals. Changing the particle injection temperature allows for control of the cooling rates in the final solution. Slower rates allow the crystals more time to fully develop and mature, contributing to better mechanical properties of the film. Coupled DSC and X-ray analysis confirmed the presence of confined interphase crystals proving that this is a viable technique for processing hybrid particles useful in graded film architectures. Akhil Have four things to say, just abbreviate

Future Work/Recommendations Improvement in the melt processing for final films improve consistency and reduce defects such as air bubbles and presence of dust particulates. Increase the sample size for data collection in order to eliminate outliers improve accuracy of resultant trends. Particle injection rate was kept consistent in this work. Future studies should add variation to this factor to further explore its effect on crystallization and/or properties of the subsequent film. Refine the overall experimental set-up to reduce sources of error such as contamination of the solution or environmental exposure. Amy Have 4 things to say, just abbr.

Acknowledgements Special thanks to: Professor Marilyn Minus Jessica Faust, Undergraduate Research Assistant Heng Li, Graduate Research Assistant YSP Staff Claire Duggan Maddy Leger Maureen Cabrera Funding for this research project was provided by the Air Force Office of Scientific Research (AFOSR FA 9950-11-1-0153) and the National Science Foundation (NSF CMMI-1351657) Amy

Thank you! Any Questions?