Evaluation of foaming polypropylene modified with ramified polymer

Abstract

Polypropylene foams have great industrial interest because of balanced physical and mechanical properties, recyclability as well as low material cost. During the foaming process, the elongational forces applied to produce the expanded polymer are strong enough to rupture cell walls. As a result, final foam has a high amount of coalesced as well as opened cells which decreases mechanical and also physical properties. To increase melt strength and also avoid the coalescence effect, one of the current solution is blend PP with ramified polymers as well as branched polypropylene (LCBPP) or ethylene-octene copolymer (POE). In this research to provide extensional properties and achieve uniform cellular structures of expanded PP, 20 phr of LCBPP or POE was added into PP matrix. The blend of PP with ramified polymers was prepared by twin-screw extrusion. Injection molding process was used to produce PP foams using azodicarbonamide (ACA) as chemical blowing agent. The morphological results of the expanded PP displayed a non-uniform geometrical cell, apparent density of 0.48 g/cm³ and cell density of 13.9 .10 4 cell/cm³. Otherwise, the expanded PP blended with LCBPP or POE displayed a homogeneous cell structure and increased the amount of smaller cells (50-100 μm of size). The apparent density slightly increased with addition of LCBPP or POE, 0.64 and 0.57 g/cm³, respectively. Thus, the cell density reduced to 65% in PP/LCBPP 100/20 and 75% in the sample PP/POE 100/20 compared to expanded PP. The thermo-mechanical properties (DMTA) of PP showed specific stiffness of 159 MPa.cm -3 .g -1 , while the sample PP/LCBPP 100/20 increased the stiffness values of 10%. Otherwise, the expanded PP/POE 100/20 decreased the specific stiffness values at -30%, in relation to expanded PP. In summary, blending PP with ramified polymers showed increasing of the homogenous cellular structure as well as the amount of smaller cells in the expanded material.

Characterization of microcellular plastics for weight reduction in automotive interior parts

“…Low solubility and diffusivity of blowing agents in PP have been determined [258,259], leading to inhomogeneous morphology along the part. On the other hand, the [261,262], ramified molecular structures [157,260] and blending with other polymer [125,[263][264][265][266]. Furthermore, it has been reported that inorganic fillers dramatically enhance cell structure of foamed polymers acting as nucleating agents.…”

Characterization of microcellular plastics for weight reduction in automotive interior parts

“…Low solubility and diffusivity of blowing agents in PP have been determined [258,259], leading to inhomogeneous morphology along the part. On the other hand, the weak melt strength promotes cell walls breakage under elongational forces while processing, causing cell coalescence and open-cell structures and decreasing mechanical properties [260].…”

“…Different methods have been conducted aimed to improve cell nucleation behavior and melt strength of PP, such as long-chain branching [261,262], ramified molecular structures [157,260] and blending with other polymer [125,[263][264][265][266]. Furthermore, it has been reported that inorganic fillers dramatically enhance cell structure of foamed polymers acting as nucleating agents.…”