THE SEMICRYSTALLINE MORPHOLOGY OF POLYAMIDE 66

FORMING AT DIFFERENT SUPERCOOLING OF THE MELT

2017 Society of Plastics Engineers Annual Technical Conference

MATERIALS

• Pelletized Zytel 101 : unlubricated and unmodified

INSTRUMENTATIONFast Scanning Chip Calorimetry (FSC): Allows for thermal preconditioning of samples

prior to XRD, POM, and AFM. The device used was a Flash DSC 1 from Mettler-

Toledo equipped with a Huber TC100 intracooler. The sensor/sample environment was

purged with nitrogen gas at a 35 mL/min.

X-ray Diffraction (XRD): Allows for analysis of crystal phases. The device used was a

Rigaku DMAX-Rapid II diffractometer equipped with a Cu X-ray tube and a graphite

monochromator. The beam diameter and exposure were 300 µm and 600 s,

respectively.

Polarized-Light Optical Microscopy (POM): Images of FSC samples subjected to a

specific crystallization history were obtained using a Leica DMRX microscope operated

in reflection mode with the sample placed between crossed polarizers.

Atomic Force Microscopy (AFM): AFM imaging was performed on a Bruker Icon I using

contact mode

RESULTS AND DISCUSSION

ABSTRACT:Fast scanning chip calorimetry (FSC) was used to prepare isothermally

crystallized samples of polyamide 66 (PA 66) in a wide range of temperatures

between 70 and 230 °C for subsequent analysis of the semicrystalline

morphology by X-ray diffraction, polarized-light optical microscopy and atomic

force microscopy. At high crystallization temperatures stable triclinic α-crystals

of lamellar shape, organized within a spherulitic superstructure are forming. At

low crystallization temperatures, in contrast, the less stable pseudohexagonal γ-

crystal structure/mesophase develops. The mesophase of PA 66, which forms

at temperatures close to the glass transition, is of grainy, non-lamellar habit, and

not organized within spherulites. The formation of such qualitatively different

semicrystalline morphologies of PA 66 is suggested being caused by different

densities of crystal nucleation, supported by observation of a bimodal

temperature-dependence of the crystallization rate. The experimental findings

reported in this work are important to allow tailoring of the microstructure of PA

66 by variation of the conditions of processing as well as contribute to the

ongoing research about crystal nucleation in polymers.

Anne M. Gohn

Advisors:

René Androsch (MLU)

Dr. Alicyn M. Rhoades (PSU)Martin Luther University: Halle-Wittenberg

Penn State University: Erie, PA

CONCLUSIONSIsothermal crystallization information has not yet been published on PA 66 systems.

This study confirms high temperature crystallization produces the stable α-structures

which form into ordered spherulites. Low temperature crystallization yields a high

nucleation density of non-lamellar γ-mesophase. POM images of the FSC samples

show there is a sharp change in structure between 110-120 °C, denoting a qualitative

change in the mechanism of crystal nucleation, from heterogeneous nucleation to

homogeneous nucleation at high and low temperatures, respectively.

ACKNOWLEDGMENTSThe author would like to thank her advisors, Dr. René Androsch and Dr. Alicyn

Rhaodes, for their guidance and support. A special thanks to Nichole Wonderling for

aiding in Xray use and Tim Tighe for AFM imaging. Also a thank you to General Motors

for their generous funding.SPE Poster Number: 2017-G04

FSC Isothermal Crystallization Method

FSC Isothermal Crystallization Method for Subsequent Characterization

WAXS Results

Polarized Light Optical Microscopy Images

X-ray results indicate a transition in crystal form from the α to γ

crystal at about 110 °C

POM images indicate a transition in crystal size and

type between 110 °C and 115 °C

AFM Images

AFM images show nanometer scale differences in crystal structure produced

at different isothermal temperatures. High

temperature crystallization creates large, ordered

spherulites. Low temperature crystallization

creates particle-like domains sizing between 10-20 nm. WAXS data concludes that

these domains represent the different crystal structures.

70 °C

70 °C

200 °C

200 °C

Heating Area Diameter = 500 µm

Sample Pan

Fast Scanning Chip Calorimeter

Wide Angle X-ray Diffraction

Sample Lateral Dimension = 200 µm

Bi-modal peak-time of crystallization curve indicates a change in

crystallization

Samples created for XRD and AFM were created

larger than for FSC thermal measurements. A sample size of 20 µm thick was cut to a 200x200 µm square.