Impact of statistical poly(propylene co-ethylene) on the thermo-mechanical properties of high-density polyethylene

Abstract

A series of high-density polyethylene and a statistical copolymer of poly(propylene-co-ethylene) blends in a wide range, namely (0, 10, 20, 30, 40, 50, 60,70, 80, 90, 100) abbreviated as HDPE/VM were systematically investigated by using a rheometer, differential scanning calorimetry (DSC) measurements, polarized optical microscopy (POM) and tensile tests. Rheometer results show that adding VM decreases dynamic viscosity, storage, and loss modulus. Han plot shows that HDPE and VM are compatible and miscible in the range from 20 to 60 VM % in the molten state. DSC results show little nucleation effect of VM on HDPE (HDPE's melt crystallization temperature shifts 2 °C higher). Moreover, a linear composition dependence of ∆cp ∆Hc, ∆Hm shows that PE and VM are most probably compatible in the molten state in composition range from 20 to 60%. However, upon crystallization, the VM and PE domains occur distinctively. The results of the tensile tests demonstrated a decrease in elastic modulus, yield stress, and ultimate tensile strength as VM content increased. At low VM content (less than 20%), high elongation at break was detected for the blends, and very fine spherulites of HDPE were found across the sample by POM.

Keywords: DSC; High-density polyethylene; Polarized optical microscopy; Rheological behavior; Statistical poly(propylene-co-ethylene); Stress-strain test.

Fig. 1

Frequency dependence of (a) complex viscosity, (b) loss modulus G″, (c) storage modulus, and (d) Han plot of pure HDPE, pure VM, and HDPE/VM blends.

Fig. 2

(a): Logarithmic scale of storage modulus & viscous modulus at different temperatures in the entire range of blend composition (b) Logarithm of the storage modulus G’ at frequency 1 Hz, measured at temperatures falling stepwise from 230 °C to 140 °C, for blends indicated.

Fig. 3

DSC cooling (a), second heating (b), (c) the extended low-temperature scale of second heating curves at 10 °C/min for HDPE/VM blends.

Fig. 4

Weight% of VM dependence of DSC transition parameters for HDPE/VM blends; maximum crystallization temperature (a), crystallization enthalpy (b), glass transition temperature (c); change in heat capacity (ΔCP) (d); maximum melting temperature (e); melt enthalpy (f).

Fig. 5

Polarised optical micrographs of HDPE/VM blends at different VM percentages as indicated.

Fig. 6

Stress-strain behavior of HDPE/VM blends.

Fig. 7

(a) elastic modulus; (b) yield stress; (c) ultimate tensile strength; (d) logarithmic scale elongation at break and weight% of VM for HDPE/VM blends.