Anomalous mechanical anisotropy of β form polypropylene sheet with N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide

An extruded polypropylene (PP) sheet in which both the chain-axes of the PP molecules and the crystalline lamellae are oriented perpendicular to the flow direction is obtained via row-nucleation on a specific needle-shaped nucleating agent, N,N’-dicyclohexyl-2,6-naphthalenedicarboxamide. The sheet shows anomalous anisotropy in dynamic tensile modulus, in which, at lower temperatures, the storage modulus in the machine direction (MD) is lower than that in the transverse direction (TD), and this behavior reverses at high temperature. Tensile tests reveal that the Young’s modulus and yield stress in the MD are higher than those in the TD. At high strain rate, the strain at break in the TD is, in contrast, markedly larger than that in the MD

Experimental and numerical study on transient elongational viscosity for PP/LDPE blends

The transient uniaxial elongational viscosity for binary blends composed of polypropylene (PP) and low-density polyethylene (LDPE) was evaluated. A strain hardening behavior is detected for the blends, although LDPE is a dispersed phase. This behavior is attributed to LDPE dispersion deformation; the LDPE forms rigid fibers because of strain hardening. Rheological properties are calculated numerically by the Phan–Thien Tanner model by assuming a symmetric geometry with a periodic structure. Based on the simulation, we propose an appropriate LDPE to modify the processability of PP, at which the strain hardening in the elongational viscosity is required

Plywood-Like Structure Of Injection-Moulded Polypropylene

Injection-moulded products having unique structure, in which the direction of molecular orientation in the skin layer is perpendicular to that in the core layer, are developed employing isotactic polypropylene with a nucleating agent. The extraordinary three-layered structure with β trigonal crystal form in the core layer, which shows higher impact strength than the conventional α monoclinic form, leads to high level of toughness. Moreover, an injection-moulded product having five-layered structure is also demonstrated in this paper. Because of the complicated crack propagation nature due to the abrupt change of molecular orientation, which avoids fractured pieces with sharp-edge, the products with plywood-likestructure will be employed in various applications to improve the safety

Optical Anisotropy in Solution-Cast Film of Cellulose Triacetate

The out-of-plane birefringence and its wavelength dispersion are studied employing solution-cast films of cellulose triacetate (CTA). In solution-cast process, CTA molecules are induced to align in the film plane. Although refractive index is the lowest in the oriented direction for the CTA films stretched more than 110%, refractive index is found to be the lowest in the normal direction for the unstretched cast film. ATR measurements reveal that in-plane alignment of the acetyl group which provides strong polarizability anisotropy is responsible for the phenomenon. Furthermore, the out-of-plane birefringence is found to increase with increasing wavelength, i.e., extraordinary wavelength dispersion, whereas a stretched CTA film shows ordinary wavelength dispersion. The level of the out-of-plane birefringence in cast films depends on the preparation conditions, which is predictable considering the evaporation rate. Moreover, it is demonstrated for the first time that the out-of-plane birefringence and its wavelength dispersion can be modified by addition of a certain plasticizer such as tricresyl phosphate (TCP). During the evaporation, TCP molecules orient in the film plane accompanying the orientation of CTA chains by intermolecular orientation correlation, called nematic interaction. This technique will widen the scope of material design of retardation films because there are numerous liquid compounds having strong polarizability anisotropy

Perpendicular orientation between dispersed rubber and polypropylene molecules in an oriented sheet

An immiscible blend of isotactic polypropylene (PP) and ethylene-butene-1 copolymer (EB) (PP/EB = 70/30) containing a small amount of N,N’-dicyclohexyl-2,6-naphthalenedicarboxamide as a nucleating agent for β-form crystals was prepared by T-die extrusion. We successfully prepared an extruded sheet, in which the orientation of the PP molecules is perpendicular to the deformation of the EB particles; i.e., the β-form crystals of PP are predominantly oriented perpendicular to the flow direction of the sheet plane (the transverse direction, TD), whereas the EB droplets are strongly deformed in the flow direction. It should be noted that the EB barely affects the crystalline form and orientation of PP. This extraordinary structure provides unique mechanical anisotropy. The tear strength in the TD sample is significantly enhanced with the anomalous crack propagation in the machine direction (MD). Moreover, the anisotropy in tensile properties such as Young’s modulus, yield stress, strain at break, and dynamic tensile modulus becomes reduced

Enhancement of glass transition temperature for poly(methyl methacrylate) by salt

We investigated the effects of two metal salts, lithium trifluoromethanesulfonate (LiCF_3SO_3) and lithium bromide (LiBr), on the glass transition temperature (Tg) of poly(methyl methacrylate) (PMMA). Both LiCF_3SO_3 and LiBr greatly enhanced the T_g of PMMA under dry conditions. However, once the sample films were exposed to humidity, the PMMA containing LiCF_3SO_3 absorbed a large amount of water, which acts as a plasticizer. As a result, the T_g shifted to a lower temperature, which limits the utility of this polymer in industrial applications. In contrast, the T_g of PMMA containing LiBr was minimally affected by the absorption of water. This phenomenon can be explained by the ion–dipole interactions with the small number of dissociated lithium cations