Measurement of thermal properties
Standard thermal analysis
Curves of the polymer blends were obtained using
DSC on a Perkin-Elmer DSC-7 instrument. Nitrogen
was used as the purge gas and an empty aluminium pan
was used as a reference. Temperature calibration of the
instrument was performed using indium as a standard
(m.p. 156.6°C). During each run the samples were
heated from 50 to 150°C at the rate of 10°C min–1. The
crystalline melting temperature of each pure polymer
was determined from the temperature axis on its curve.
These temperatures (T1 and T2) were used in programming
the optimum TSIA processes for the blends on
the basis that maximum segregation and crystallization
would occur at these temperatures.
Two-step isothermal annealing
The optimized TSIA process for blends of LLDPE1
through LLDPE5 with LDPE involved heating each
blend to 180°C on the hot stage, maintaining this temperature
for approximately 1 min, and then cooling at
the rate of 2°C min–1 to the temperature of the first
crystallization minimum (T1). The sample was held at
this temperature for 2 h, after which it was cooled at
the rate of 2°C min–1 to the second minimum (T2)
where it was held for 4 h. The sample was then cooled
to 20°C at the rate of 10°C min–1.