Masaki Tsuji

Crystal structure of stereocomplex of poly(L-lactide) and poly(D-lactide)

Abstract An equimolar mixture of poly(L-lactide) and poly(D-lactide) was crystallized into a stereocomplex whose crystal system is triclinic (P1) with cell dimensions: a = 0.916 nm, b = 0.916 nra, c (chain axis) = 0.870 nm, α = 109.2°, β - 109.2°, and γ = 109.8°. In the unit cell, a poly(L-lactide) segment and a poly (D-lactide) segment are contained as a pair and packed laterally in parallel fashion. The L- and D-poly(lactides) in the complex take a 31 helical conformation, which is a little extended from a 103 helix in the homopolymer crystal with the α-form. Homopolymers are also able to take the 31 helical conformation and form the β-form crystal. The 31 helix in the homopolymer crystal is less stable than the 103 one, and hence the β-form is easily transformed to the α-form by annealing.

Phase separation behavior in aqueous suspensions of bacterial cellulose nanocrystals prepared by sulfuric acid treatment.

Phase separation phenomena of aqueous suspensions of cellulose nanocrystals have been studied for bacterial cellulose (BC) prepared by sulfuric acid hydrolysis. Suspensions at concentrations above 0.42 wt % separated into the isotropic and chiral nematic phases with a clear phase boundary. The shape and size distribution of BC nanocrystals in both the phases were determined by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The surface charge density was determined by conductometric titration. The effects of added NaCl (0-5.0 mM) on the phase separation behavior of the aqueous suspensions were investigated for a fixed total cellulose concentration. The volume fraction of the chiral nematic phase had a minimum value at a NaCl concentration of ca. 1.0 mM. At NaCl concentrations ranging from 2.0 to 5.0 mM, the suspensions did not separate into two phases, but became entirely liquid crystalline. The size of the ordered domains in the anisotropic phase decreased with an increase in the NaCl concentration from 0 to 2.75 mM. At 2.75 mM, only tactoids were observed in the entire region. At 5.0 mM, chiral nematic domains were no longer observed. The chiral nematic pitch decreased with increasing concentration of added NaCl, reached a minimum value at approximately 0.75 mM, and then increased sharply with the NaCl concentration up to 2.0 mM.

In Situ Crystallization of Bacterial Cellulose III. Influences of Different Polymeric Additives on the Formation of Microfibrils as Revealed by Transmission Electron Microscopy

Effects of polymer additives on the formation of microfibrils of bacterial cellulose have been examined by transmission electron microscopy. Among additives with different degrees of polymerization (DP) or substitution (DS), carboxymethyl cellulose sodium salt (CMC) with DP = 80 and DS = 0.57 is the most effective in producing separate, smaller-size microfibrils. By increasing the concentration of this CMC from 0.1 to 1.5%, the percentage of microfibrils measuring 3–7 nm wide is increased and levels off at around 1.0%. Other polymer additives such as xyloglucan are less effective than CMC in producing microfibrils with smaller sizes and the resulting microfibrils still tend to aggregate. The number of charged substituents and the molecular weight seem to be important factors in the production of highly separate smaller-size microfibrils. The reduction in average microfibril size is well correlated to the decrease in mass fraction of cellulose Iα in bacterial cellulose crystals. On the basis of these results, the mechanism of the crystallization of celluloses Iα and Iβ is discussed. The effect of colony types, smooth and rough, on the formation of microfibrils in the presence of CMC is also described.

A study on the structural changes during uniaxial drawing and/or heating of poly(ethylene naphthalene-2,6-dicarboxylate) films

The structural changes in the uniaxial drawing process of an unoriented amorphous film of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) and in the heating process of an oriented amorphous film of PEN were studied using X-ray diffraction apparatus equipped with imaging plates. This apparatus allows us to record a time-resolved series of two-dimensional patterns of wide-angle X-ray diffraction in rapid succession, and, therefore, we can follow the structural changes during uniaxial deformation and/or thermal treatment processes. The results are as follows: (1) When an unoriented amorphous PEN film was stretched below Tg (= 117 °C), it could be elongated up to a draw ratio (DR) of 4–5 via neck formation and became an oriented amorphous film. (2) In the heating process of the oriented amorphous film (DR = 3.6, 65 °C), crystalline reflections started to appear near 120 °C, accompanied by streaks on the off-equatorial layer lines. The existence of these streaks on such layer lines indicates a lattice distortion due to the axial shift of neighbouring chains along the chain axis with respect to one another. Finally the film exhibited a fibre structure (transverse isotropy). (3) When an unoriented amorphous PEN film was drawn at 150 °C, the film exhibited a fibre structure accompanied by a lattice distortion that is similar to that mentioned above, and thereafter frequently showed so-called double orientation (uniplanar axial orientation: (10)[001]) in which naphthalene rings in the main chain are preferentially aligned parallel to the film surface despite the fact that the film was deformed in the mode of uniaxial free-width drawing.

Direct imaging of molecular chains in a poly(p-xylylene) single crystal

Abstract Individual chains comprising a β-form poly( p -xylylene) (PPX) single crystal were resolved with a high resolution electron microscope (JEM-500). In a polymer crystal the important limiting factor for resolution is radiation damage. The total end point dose of a PPX crystal is about 0.5 coulomb cm −2 for 500 kV electron irradiation which is more than 20 times greater than that for a polyethylene crystal. The high resolution image obtained was processed by optical filtering to reduce noise due to the granularity of film. The processed image, which corresponds to the ab -plane projection of polymer chains, shows clearly the mutual arrangement of each molecule in the crystal. This high resolution image is sufficient to provide a starting point for determining the unknown crystal structure of the β-modification of PPX.

Structure development in the uniaxial-drawing process of poly(ethylene naphthalate)

Amorphous films of poly(ethylene naphthalene-2,6-dicarboxylate) were drawn isothermally up to desired draw ratios at 130, 140, 150 and 160°C mainly to study structure formation during uniaxial drawing by wide-angle X-ray diffraction (WAXD). The results were analysed in comparison with stress-strain curves in order to find the draw ratio associated with the onset of crystallization at the above-mentioned temperatures. To obtain further detailed information, birefringence and density were measured for the films drawn at 150°C to elucidate the relationship between the degree of chain orientation and the crystallinity. A series of results was discussed in relation to previously reported interesting phenomena of the time-resolved two-dimensional WAXD patterns recorded using the imaging plate system (Polymer 1995, 36, 291).

Structural analysis of β-form poly(p-xylyene) starting from a high-resolution image

Abstract The crystal structure of β-form poly( p -xylylene) is analysed starting from a high-resolution image of a single crystal of this polymer. The high-resolution image corresponding to the projection of molecules onto the ab -plane along the chain axis shows clearly the mutual position of each molecule in a unit cell. The molecules are aligned wavily in the direction along the a -axis and the rough positions of their centres in a unit cell can be determined from the image. The refinement of the structure is carried out by the usual least-squares method using the intensities of electron and X-ray diffractions. The space group of the β-form is trigonal, P3, and the lattice dimensions are a =2.052 nm, c =0.655 nm and γ =120°. The unit cell contains 16 molecules and one of them is considered to occupy statistically one of three equivalent orientations so as to satisfy the P3 symmetry.

In situ copolymerization behaviour of zinc dimethacrylate and 2‐(N‐ethylperfluoro‐octanesulphonamido)ethyl acrylate in hydrogenated nitrile–butadiene rubber during peroxide crosslinking

The in situ copolymerization behaviour of zinc dimethacrylate (ZMA) and 2-(N-ethylperfluoro-octanesulphonamido)ethyl acrylate (RfSA) in hydrogenated nitrile-butadiene rubber (HNBR) initiated with di-tert-butyl peroxy di-isopropylbenzene (PO) was studied by transmission electron microscopy, dynamic mechanical analysis, surface tension and surface composition. About 80% of the monomers were copolymerized within the half-lifetime of PO at 140 °C. The compositions of the copolymers were almost the same as the co-monomer compositions at high conversions. The crosslinking of the HNBR proceeded within the press time of 300min. At the initial stage of the copolymerization, ZMA seemed to form cluster domains in the HNBR matrix, followed by a decrease in the domain size to become too small to exhibit a tans peak of the clusters on phase separation between the matrix and the copolymer. The surface compositions were different from the average compositions. The RfSA unit in the copolymer was segregated at the surface ofthe vulcanizates with an increase in the press time. During phase separation and migration of the copolymer towards the surface, Zn and N were oxidized and ionized. Finally, the in situ copolymerizations formed a continuous network structure of which the domain size was 30-60nm.

TEM study of band-like cellulose assemblies produced by Acetobacter xylinum at 4 °C

Two kinds of band-like cellulose assemblies, coarse and densestructures, are produced in Hestrin–Schramm medium at 4 °Cusing smooth colonies isolated from Acetobacter xylinumATCC23769, whereas ribbon cellulose assemblies are produced by the samecoloniesat 28 °C. The dense and the coarse band-like assembliesconsist of many strand-like cellulose entities (‘strands’) and areextruded perpendicularly to the long axis of the bacterial cell. In an earlystage of incubation at 4 °C, the dense band-like assembly isproduced and the number of strands decreases gradually with increasingincubation time at 4 °C, probably because the number of activeTC subunits decreases as a result of the low-temperature shock for thebacteria.In contrast, the coarse band-like assembly is clearly observed after about 1h of incubation at 4 °C. The number of strands inthe coarse band-like assembly is about one third of that of the dense band-likeassembly and does not change during the incubation time of about 6h. In the selected-area electron diffraction (ED) experiment, thedense band-like assembly gives crystalline reflections corresponding to thecellulose II type crystal, while the coarse band-like assembly does not giveanycrystalline reflections under the same ED conditions.

TEM observation of natural rubber thin films crystallized under molecular orientation

Morphology of natural rubber (NR) thin films crystallized under molecular orientation was examined by transmission electron microscopy (TEM). A thin film of NR (RSS#1) was made by casting its n-hexane (or benzene) solution onto the water surface, and prestretched up to a desired amount of strain (%). Each of the specimens thus prepared was introduced into a TEM column and isothermally crystallized at -25 °C with a cryo-transfer specimen-holder. Morphological observations in bright- and dark-field imaging modes revealed directly that the length of the lamellae, which were oriented perpendicular to the stretching direction, decreased with increasing strain. The result seems to be related to the population density of y-filaments (named by Andrews) generated only by prestretching. Time-resolved bright-field observations by in situ TEM of the thin film prestretched up to a strain of 200% revealed the following. Though the film gave crystalline reflections in its selected-area electron diffraction even before isothermal crystallization, no well-defined lamellae were recognized. Subsequent isothermal crystallization for 2 h, however, formed well-defined lamellae oriented perpendicular to the stretching direction. This observation, conceivably, suggests that y-filaments were formed immediately by prestretching and then the lamellae were nucleated on the γ-filaments at -25 °C.