Mechanical properties and morphology of polyethylene–polypropylene blends with controlled thermal history

✍ Scribed by Jun Li; Robert A. Shanks; Yu Long

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 632 KB
• Volume: 76
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(20000516)76:7<1151::aid-app19>3.0.co;2-h

✦ Synopsis

The effect of time-temperature treatment on the mechanical properties and morphology of polyethylene-polypropylene (PE-PP) blends was studied to establish a relationship among the thermal treatment, morphology, and mechanical properties. The experimental techniques used were polarized optical microscopy with hotstage, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and tensile testing. A PP homopolymer was used to blend with various PEs, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and very low density polyethylene (VLDPE). All the blends were made at a ratio of PE:PP ϭ 80:20. Thermal treatment was carried out at temperatures between the crystallization temperatures of PP and PEs to allow PP to crystallize first from the blends. A very diffuse PP spherulite morphology in the PE matrix was formed in partially miscible blends of LLDPE-PP even though PP was present at only 20% by mass. Droplet-matrix structures were developed in other blends with PP as dispersed domains in a continuous PE matrix. The SEM images displayed a fibrillar structure of PP spherulite in the LLDPE-PP blends and large droplets of PP in the HDPE-PP blend. The DSC results showed that the crystallinity of PP was increased in thermally treated samples. This special time-temperature treatment improved tensile properties for all PE-PP blends by improving the adhesion between PP and PE and increasing the overall crystallinity. In particular, in the LLDPE-PP blends, tensile properties were improved enormously because of a greater increase in the interfacial adhesion induced by the diffuse spherulite and fibrillar structure.