The Binary System Isotactic Polypropylene/Bis(3,4-dimethylbenzylidene)sorbitol:  Phase Behavior, Nucleation, and Optical Properties

Abstract

The phase behavior of the binary system consisting of the commercial nucleating and clarifying agent 1,3:2,4-bis(3,4-dimethyldibenzylidene)sorbitol (DMDBS, Millad 3988) and isotactic polypropylene (i-PP) was investigated over the entire concentration range by means of differential scanning calorimetry (DSC), rheology, and optical microscopy. Experimental phase diagrams were constructed from data obtained in melting and crystallization studies, and a simple binary monotectic is advanced. Distinct regimes in the phase diagram, which apparently dictate nucleation and clarification of i-PP by DMDBS, are discussed. A maximum increase in the crystallization temperature of i-PP due to the nucleating action of DMDBS was observed in compositions containing between 0.2 and 1 wt % of the latter. Liquid−liquid phase separation was observed at elevated temperatures for i-PP/DMDBS mixtures comprising more than 2 wt % of DMDBS. A study of the optical properties of the i-PP/DMDBS system revealed that values for haze and clarity of injection-molded plaques progressively decreased and increased, respectively, in the concentration range between 0.2 and 1 wt % DMDBS in i-PP; at DMDBS concentrations exceeding 1 wt % the presence of the additive had an adverse effect on the optical properties of i-PP. Finally, a surprisingly strong influence of cooling kinetics on the phase behavior and, consequently, on the optical properties of the i-PP/DMDBS system was detected, which is of obvious relevance for industrial applications.

Effect of the Molecular Structure of the Polymer and Nucleation on the Optical Properties of Polypropylene Homo- and Copolymers

“…In the case of soluble clarifiers spherulites might not even form, often a network structure and a microcrystalline structure have been observed in their presence [10][11]31 . We may conclude from these results that the main factor determining haze is the size of the supermolecular units formed during the crystallization of our polymers, and they decrease with increasing amount of nucleating agent.…”

“…Low haze materials are usually prepared from random copolymers and optical properties are improved further by the use of clarifiers based on different sorbitol derivatives [5][6][7][8][9] . These latter additives dissolve in the polymer generating a microcrystalline structure and improve haze considerably [10][11] . In the last decade a relatively new family of nucleating agents based on trisamide derivatives appeared as the competitor of sorbitol clarifiers [12][13][14][15] .…”

“…However, the efficiency of the clarifier depends very much also on the characteristics of the polymer used and on processing conditions, as mentioned above. Quite a few papers are dealing with the effect of clarifiers on the optical properties of PP 10,[16][17][18] , but according to our literature survey very few relates the achieved characteristics to the structure of the polymer 19 . The selection of the polymer used usually occurs on trial and error bases.…”

Using rheometry to determine nucleation density in a colored system containing a nucleating agent

“…Adding a nucleating agent to a semi-crystalline polymer is a common way to control crystallization and tailor mechanical and optical properties (Kristiansen et al 2003(Kristiansen et al , 2005Kurja and Mehl 2001;Menyhárd et al 2009). The interface between the nucleating agent and the polymer melt has a high surface energy, which reduces the energy barrier associated with the formation of a nucleus.…”

Controlled Crystallization of Isotactic Polypropylene Based on α/β Compounded Nucleating Agents: From Theory to Practice

“…NA as one of the additives presents a role of increasing the nucleation density of polymer greatly and enhancing the nucleation rate dramatically so as to have a great impact on the mechanical properties of polymer (Kristiansen et al, 2003;Romankiewicz et al, 2004;Tenma & Yamaguchi, 2007). So far, two kinds of NAs, phase and phase NAs discriminated by the form of iPP they induce have been widely put into use in modifying iPP.…”