Rejuvenation of PLLA: Effect of plastic deformation and orientation on physical ageing in poly(l‐lactic acid) films

Poly(l ‐lactic acid) (PLLA) is a bio‐degradable polyester which exhibits brittle behaviour due to relatively fast physical ageing of the amorphous phase. This work describes the effects of thermal rejuvenation and molecular orientation of the amorphous phase on this physical ageing process. Uniaxial compression testing showed that physical ageing of the amorphous phase increases the yield stress and the associated strain softening response, both contributing to the observed embrittlement of PLLA in tension. Molecular orientation at constant crystallinity was applied by uniaxial and biaxial plastic deformation just above the glass transition temperature, up to plastic strains of 200% to avoid strain‐induced crystallisation. Using stress‐relaxation experiments combined with tensile testing, both as a function of ageing time, it is shown that both uniaxial and biaxial plastic deformation in excess of 150% plastic strain, decelerates and possibly prohibits the physical ageing process. The oriented monofilaments and films have improved mechanical properties such as stiffness, strength and strain‐to‐break, which were not affected by physical ageing during the whole testing period (40 days). In addition, plastic deformation to higher draw ratios and/or higher temperatures strongly enhanced crystallinity and resulted in PLLA monofilaments and films that also exhibited tough behaviour, not affected by physical ageing. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2233–2244     

Traveling Waves in Porous Media Combustion: Uniqueness of Waves for Small Thermal Diffusivity

We study traveling wave solutions arising in Sivashinsky’s model of subsonic detonation which describes combustion processes in inert porous media. Subsonic (shockless) detonation waves tend to assume the form of a reaction front propagating with a well defined speed. It is known that traveling waves exist for any value of thermal diffusivity [5]. Moreover, it has been shown that, when the thermal diffusivity is neglected, the traveling wave is unique. The question of whether the wave is unique in the presence of thermal diffusivity has remained open. For the subsonic regime, the underlying physics might suggest that the effect of small thermal diffusivity is insignificant. We analytically prove the uniqueness of the wave in the presence of non-zero diffusivity through applying geometric singular perturbation theory. Dedicated to Mr. Brunovsky in honor of his 70th birthday.     

Metal-complex catalysis during the reduction of functional groups by sodium borohydride in the synthesis of pyrrolidine derivatives

A selective method was developed for the reduction of functional groups with sodium borohydride using complexes of CoCl₂ and CuCl₂ with triethylbenzylammonium chloride and cobalt and copper mesotetra[4-(2-hydroxyethyl)pyridyl]porphyrinates as catalysts. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 205–208, February, 2006.     

On almost hypoelliptic polynomials increasing at infinity

It is proved that a polynomial (the symbol of a differential operator), the Newton polygon of which is a rectangular parallelepiped with a vertex at the origin, is almost hypoelliptic if and only if it is regular. Also some algebraic conditions of almost hypoellipticity are obtained for nonregular polynomials increasing at infinity. The results are unimprovable for polynomials of two variables.     

On smooth solutions of a class of almost hypoelliptic equations

For a class of non-degenerate (regular) almost hypoelliptic equations, which are partially hypoelliptic with respect to certain variables, infinitely differentiable in a specific strip solutions are extracted.     

Vibrational spectra of l-lysine monohydrochloride dihydrate and its two anhydrous forms

ATR FTIR and Raman spectra of l-Lys·HCl·2H₂O and two crystalline forms of anhydrous l-Lys·HCl are reported and discussed. Distinction with earlier published IR spectra of l-Lys·HCl·2H₂O registered by the KBr pellet method is explained by distortion of the spectra because of possible ionic exchange and partial decomposition.     

3-Methoxalylchromone--a novel versatile reagent for the regioselective purine isostere synthesis

The first synthesis of 3-methoxalylchromone was described. The reaction of the latter with electron-rich aminoheterocycles afforded a set of heteroannelated pyridines bearing a CO(2)Me substituent located at the α-position of the pyridine core.     

Comparison of the Strengths of Polynomials of Two Variables

In this paper, for homogeneous polynomials of two variables we find necessary and sufficient conditions for comparison of the weighted strengths of these polynomials. The conditions are stated in terms of orders and multiplicities of the zeros of the considered polynomials.     

On unconditional basis property of sine and cosine systems

It is proved that the systems of functions {sin(n−β x} _n=1^∞ and {cos(n−β x} _n=1^∞ are not unconditional bases in the spaces L ^p (0, π), p≠ 2.