Graded Architecture Composites

Amy Huang – Newton North High SchoolAkhil Meka – Chelmsford High SchoolProfessor Marilyn Minus

Background

Materials Science and Engineering, William D. Callister Jr, Wiley Schematic courtesy of Jessica Faust

Lamellar crystals

Hybrid particles with lamellae (confined)

Semicrystalline matrix comprised of spherulites

Composite material

Alumina plateletAlumina with CNT crystal seeds

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

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.

Processing

Actual representation of powder after filtering

Syringe

Beaker

Hot Plate

Processing

Melt Film

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

Actual representation of film after melting

Temperature Profiles

Undercooling/ΔT

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

Lamellae Crystallization=XC, XRD-XC, DSC

Mechanical Testing

Mechanical testing performed by an Instron machine

Mechanical TestingAlumina Particle

Solution Temperature

(°C)

Modulus, E

(MPa)

Tensile Stress, σ

(i.e., Strength)

(MPa)

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 31.1424.8 (only

one sample tested)

51.2 895 ± 30.9 35.3 ± 0.7 36.9 ± 17.1

bubbles

scratches

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

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.

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.

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.

AcknowledgementsSpecial thanks to: ● Professor Marilyn Minus● Jessica Faust, Undergraduate Research

Assistant● Heng Li, Graduate Research Assistant● YSP Staff

o Claire Duggano Maddy Legero 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)

Thank you! Any Questions?