Effect of Long-chain Branching on the Foaming of Polypropylene with Azodicarbonamide

Abstract

In this article the influence of long-chain branching on the foaming behavior of polypropylene (PP) is investigated. Different branching contents are achieved by blending a linear PP (L-PP) and a long-chain branched PP (LCB-PP). Whereas, the L-PP does not exhibit any strain hardening in laboratory stretching experiments, blends with amounts of the LCB-PP higher than 2 wt% already show a pronounced strain-hardening behavior. The strain hardening increased with a growing amount of the long-chain branched PP. A laboratory scale foaming apparatus based on a capillary rheometer is developed for the foaming experiments. In foaming tests with azodicarbonamide as chemical blowing agent, a significant improvement of the foaming behavior with respect to a higher expansion ratio, a lower amount of connected cells, and a more homogeneous cell size distribution is found with increasing content of the LCB-PP up to a concentration of 50 wt%. At this concentration, the foaming behavior of the LCB-PP is reached. The results demonstrate that low amounts of long-chain branching can significantly improve the optimal foaming process of PPs with a chemical blowing agent, and that additions of the linear material up to 50 wt% to the LCB-PP do not have any influence on the favorable foaming performance of the long-chain branched PP.

The effect of strain-hardening on the morphology and mechanical and dielectric properties of multi-layered PP foam/PP film

“…Thermoplastic foams can be defined by the morphology of the cell, i.e., closed cell or open cell foams [4][5]. In closed cell foams, discrete cavities are Among thermoplastic foams, polypropylene (PP) foams are potentially interesting for foam applications due to their thermal and physical properties such as a comparably low density, relatively high service temperature, good impact strength, and excellent chemical resistance [6][7][8][9][10]. However, PP has a rather weak melt strength and this often causes fracture of thin parts such as bubble coalescence and rupture during the foaming process [11][12][13][14][15], thus making it difficult to obtain closed-cell microcellular PP foam.…”

Rheometric study of the gelation and fusion processes of poly(vinyl chloride‐co‐vinyl acetate) plastisols with different commercial plasticizers

“…Depending on the plasticizer compatibility with the PVC resin and the rate of applied heating, these interactions start at different temperatures. These phenomena can be identified as a series of slope changes on the complex viscosity/temperature curve [49, 50]. Beyond a certain temperature, where these phenomena no longer occur, the viscosity of the sample continuously decreases.…”

Cellulose Acetate for Thermoplastic Foam Extrusion

“…The melt viscosity results agree well with previous results obtained from melt processing (subchapter 2.1) and thermal characterization (subchapter 2.2). With respect to foam extrusion, melt viscosities and melt flow behavior of these externally plasticized CA compounds are in range of typical foam polymers such as PS, branched PE, and branched PP [10,11,15,45,46].…”

“…A broad MWD or high PD, the incorporation of side chains or branched structures as well as blending linear with branched or cross-linked polymers are favorable for good foam extrusion behavior. Blends of linear and branched polypropylene (PP), crosslinked polyethylene (PE) or blends of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are good examples for improved melt strength, melt extensibility, and consequently good foaming behavior [4,[9][10][11][12][13]. Chain extension of recycled poly(ethylene terephthalate) (PET) significantly improves the rheological properties and foaming behavior [14].…”