Modulus enhancement of polypropylene by sorbitol nucleating agent in flow field

Abstract

The rigidity of an injection‐molded isotactic polypropylene (PP) containing 1,3:2,4‐bis‐o‐(4‐methylbenzylidene)‐D‐sorbitol (MDBS) as a crystal nucleating agent can be enhanced by selection of appropriate processing conditions. A new method by differential scanning calorimetry measurements showed that the dissolution temperature of 0.4 wt.% MDBS in molten PP is around 210°C. When injection molding was performed below the dissolution temperature, for example, 190°C, the molecular orientation of PP was greatly enhanced. Although this is an anomalous condition for the system to expect good transparency, the product obtained showed a high flexural modulus. In contrast, with high‐temperature processing at 240°C, that is, conventional condition, the modulus decreased because of poor molecular orientation. Transmission electron microscopy observation revealed that MDBS fibrils strongly orient to the flow direction under the low‐temperature processing, in which network structure of MDBS fibers is not detected. The oriented MDBS fibers led to a well‐developed shish‐kebab structure, which is responsible for the pronounced rigidity.

Role of Shear Flow on Structure Development during Post-Processing Annealing for Poly(lactic acid)

“…Moreover, the alignment of shish to the flow direction led to the orientation of crystalline chains grown during annealing. Similar results were recently reported for isotactic polypropylene containing fibrous nucleating agents and polyhydroxyalcanoate [ 38 , 39 , 40 ], although the crystal growth did not occur during post-processing annealing in these studies. This anomalous growth of molecular orientation for PLA will be important for the dimensional control and mechanical properties, such as modulus and its anisotropy.…”

Nanolignin as Nucleating Agents Promoting Crystallization of Isotactic Polypropylene

“…NAs can be divided into natural NAs, synthetic NAs, and inorganic NAs. Te natural NAs mainly include rosin, sorbitol, and sorbitol derivatives such as dibenzylidene sorbitol and 3, 4-dimethyldibenzylidene sorbitol [13][14][15][16][17][18][19][20][21][22][23][24]. Te synthetic NAs include polycyclic aromatic hydrocarbons, organic acids/salts, amides, [25] benzoic acid salts, [26] hydrazide compounds, [27] and various organic pigments.…”

Effect of Ultra-High-Molecular-Weight Molecular Chains on the Morphology, Crystallization, and Mechanical Properties of Polypropylene

“…Molecular weight and molecular weight distribution strongly affect various properties of polymeric materials [ 1 ] as well as branch structure [ 2 , 3 ] and the addition of nanofillers [ 4 , 5 , 6 , 7 ]. The physical and mechanical properties of polymeric materials such as viscosity, diffusion coefficient, drawability, and toughness are strongly influenced by the molecular weight and its distribution [ 8 , 9 , 10 , 11 ].…”