Hydrogenated Petroleum Resin Effect on the Crystallization ofIsotactic Polypropylene
ABSTRACT: The influence of the hydrogenated petroleum resin P125 on the crystallization behavior, crystallization kinetics, andoptical properties of polypropylene (PP) were investigated. The results of differential scanning calorimetry, successive self-nucleation,and annealing fractionation demonstrated that P125 reduced the interaction between the PP molecules, decreased the crystallization,prevented PP from forming thick lamellae, and encouraged the formation of thin lamellae. The isothermal crystallization kinetics,self-nucleation isothermal crystallization kinetics, and polarized optical microscopy observations showed that P125 slightly decreasedthe nucleation rate, significantly decreased the crystal growth rate, generally reduced the overall crystallization rate, and effectivelydeceased the crystallite sizes of PP. The optical properties studies showed that P125 effectively decreased the haze and increased thesurface g lossiness and yellowness index of PP.VC2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 25–38, 2013
Petroleum resin comes from blends of unsaturated monomersobtained as volatile byproducts in the cracking of natural gas,gas oil, and so on. The unsaturated monomers consist ofmono-olefins, diolefins, cyclic olefins, and vinyl derivatives ofaromatic hydrocarbons. A hydrogenate procedure is often usedto obtain hydrogenated petroleum resin (HPR). HPRs are com-monly characterized by their color, iodine number, specificgravity, solution viscosity, softening point, and aniline point.They have water resistance, wide compatibilit y with polyolefins,chemical neutrality, good electrical properties, and well-balancedadhesive characteristics.Because of the advantages mentioned previously, HPRs arewidely added to polypropylene (PP) to modify its structure,morphology and properties, especially in film production. Theconsumption of HPRs in PP applications is large. Researchershave mainly paid attention to the phase behavior crystallization,morphology, and properties of PP blended with low-molecularresins similar to HPRs, for instance, hydrogenated oligocyclo-pentadiene.1–4They have also investigated the crystallization,morphology, and properties of PP/HPR mixtures;5–7great pro-gress in investigating the phase structure, overall crystallizationbehavior, and structure has been made. However, in previousstudies, the detailed influence of HPRs on the crystallization behavior and crystallization kinetics (e.g., the separated primarynucleation kinetics and crystal growth kinetics) is still not clearyet; this is of great importance in determining the multiscalemorphology and properties of PP.8,9Currently, the applicationof HPRs on PP is still in its experiential stage, and this hasrestrained the scientific application of HPRs and the propertydesign of PP products.In classical crystallization theories, the temperature dependenceof the overall crystallization rate (Go) can be expressed by two ex-ponential factors: the nucleation term and the crystal growth(molecular transport) term.10–13For many semicrystalline poly-mers, including PP, it has been found that these two factors havedifferent crystallization peak temperature (Tc) dependence behav-iors and thereby display a bell-shaped temperature dependence ofGo, with a maximum Goat a maximum Tc.10–13At low super-coolings (the high-crystallization region), the thermal movementof the molecular chains is intense, and the crystal growth term isdominant; At high supercoolings (the low-Tcregion), the molec-ular chain diffusion becomes very difficult, and the nucleationterm is dominant. As the temperature decreases and evenapproaches the glass-transition temperature (Tg), the crystalliza-tion nearly ceases. On the other hand, it is necessary for the meltto be supercooled to form stable nuclei; therefore, the higher thesupercooling degree is, the more favorable the thermodynamicconditions will be for nuclei formation.