Characterization, Solar Reflectance, and Crystal Properties of Polyethylene and Ethylene Copolymer after Thermal Treatment

Abstract

Various kinds of polyethylene and ethylene copolymers were prepared by non-isothermal crystallization and isothermal crystallization methods. Solar reflectance of all samples was determined by a series of characterization (UV-vis-NIR measurement, wide-angle X-ray diffraction, differential scanning calorimetry analysis, polarized optical microscopy). It was found that lamellar thickness, degree of crystallinity, and microstructure played an important role in affecting the solar reflectance of these polymers. Long-branched chains in ethylene copolymers lowered the solar reflectance by decreasing lamellar thickness and the degree of crystallinity of these polymers. The isothermal crystallization method is a way to promote lamellar thickness and the degree of crystallinity, and make the microstructure more compact.

Keywords:

• Crystallinity
• Lamellar thickness
• Polyethylene
• Solar reflectance

Acknowledgments

The financial support for this work was provided by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

Notes

All reflectance values of different bands (U, V, N) were calculated by Equation (1); the total solar reflectance values S were calculated by Equation (2).

All reflectance values of different bands (U, V, N) were calculated with Equation (1); the total solar reflectance values S were calculated by Equation (2).

L ₁₁₀: lamellar thickness corresponds to (110) crystal plane; L ₂₀₀: lamellar thickness corresponds to (200) crystal plane.

T _on : onset melting temperature; T _{p 1}: melting peak temperature of peak I; T _{p 2}: melting peak temperature of peak II; T _f : final melting temperature; ΔH _m : melting enthalpy; X _c : degree of crystallinity.