Properties of polyethylene‐polypropylene blends: Crystallization behavior

Abstract

The crystallization behavior of high density polyethylene/isotactic polypropylene blends (HDPE/PP) was investigated. The overall kinetics of crystallization of HDPE may be strongly influenced by the addition of a small fraction of PP. At 398 K the half crystallization time of the blend containing 10% by weight of P P is around three times larger than for pure polyethylene. This effect may be accounted for by an increase in the melt viscosity of liquid HDPE caused by PP molecules. For crystallization temperatures high enough to prevent HDPE crystallization (T, > 400 K), the presence in the melted blends of liquid HDPE influences the crystallization of PP. In fact, the half time of crystallization of P P increases with increasing the fraction of HDPE in the blend. The kinetics show a minimum at a well defined composition (around 60% in PP) before phase inversion. The same trend is observed when the surface free energy of folding and the lamellar thickness of crystals are reported as function of composition.

Evaluation of the crystallization kinetics and melting of polypropylene and metallocene‐prepared polyethylene blends

“…Δ E was calculated with the Williams–Landel–Ferry equation as follows:48, 49 where T g is the glass‐transition temperature and C 1 and C 2 are constants that generally are considered to be 17,240 J/mol (4120 cal/mol) and 51.6 K, respectively 50…”

“…The spherulitic growth rate ( g ) is closely related to Z and t 1/2 as follows: For the lateral surface energy of linear polymer crystals, the following relation holds:48, 53 Combining eqs. (8–14), we can write the following expression applicable to regime III crystallization kinetics:47, 48, 54 In this study, regardless of the blend composition, T g , as measured by dynamic mechanical thermal analysis, was taken to be 268 K. The value for T g of PP was used because limited solubility was found between the two polymers and also because PP alone crystallized 50…”

Crosslinked Polymers and Rubber Elasticity

“…The diene is often a bicyclic compound introduced at the 2% level to provide crosslinking sites: (9.96) It must be pointed out that although both polyethylene and polypropylene are crystalline polymers, the random polymer at midrange compositions is totally amorphous. These materials, with a glass transition of -50°C, make especially good elastomers for toughening polypropylene plastics (134)(135)(136).…”

Thermal and Crystallization Properties of HDPE and HDPE/PP Blends Modified with DCP

“…[11][12][13][14][15][16] But the effect of chemical compatibilization on the thermal and crystallization properties are only reported by a few authors. The crystallization behavior of PE and PP blends without compatibilization has been studied extensively.…”