Noncrystalline amorphous component

Our broad-line XH NMR analysis showed that this type of sample generally consists of the phase structure of lamellar crystallites and noncrystalline overlayer with a negligible amount of the noncrystalline amorphous phase [16,62]. In broad-line H NMR spectra of solution-grown linear polyethylene samples, a narrow component that suggests the existence of a liquid-like amorphous phase is hardly recognized. In Table 2, the three-component analysis of the broad-line XH NMR spectra of linear polyethylene samples with different molecular weights that were crystallized isothermally from 0.08% toluene solution at 85 °C for 24 hours under a nitrogen atmosphere is summarized. 

The mass fraction of the narrow component that corresponds to the rubbery noncrystalline amorphous phase is as small as 0.003-0.006. The mass fraction does not increase appreciably with increasing temperature, but stays almost unchanged up to 70 °C. Hence, it is concluded that solution-grown samples do not actually comprise a rubbery amorphous phase. This conclusion is confirmed by high-resolution solid-state 13C NMR with more detailed information. 

Fig. 19. Line shape analysis of the equilibrium spectrum of P420. The large dotted Lorentzians centered at 32.4 and 30.5 ppm and rather wide dotted Lorentzian centered at 32 ppm represent the orthorhombic crystalline and noncrystalline amorphous phases and crystalline-amorphous interphase, respectively. The dotted curve that is almost completely superimposed on the experimental spectrum indicates the composite curve of the component Lorentzians. dashed Weakly Lorentzians at 39, 34, 28, and 26 ppm represent the contributions from the methine and methylene carbons (a and p to the methine and methylene in the ethyl side group), respectively...

Carbohydrates and proteins are typical hydrophilic components of concentrated food systems. These components tend to form amorphous, noncrystalline structures at low water contents (White et al. 1966 Slade et al. 1991 Roos 1995). Well-known food processes resulting in glass formation by amorphous or partially amorphous food components include baking, extrusion, dehydration and freezing (Roos 1995). In these processes, removal of water as part of the manufacturing process results in the formation of a noncrystalline, amorphous state, which is extremely sensitive to water and may show various time-dependent changes causing loss of quality and reduced shelf life. 

Although we will concentrate on crystalline solids in this book, there are many important noncrystalline (amorphous) materials. An example is common glass, which is best pictured as a solution whose components are frozen in place before they can achieve an ordered arrangement. Although glass is a solid (it has a rigid shape), a great deal of disorder exists in its structure. 

Since Holmes observation of the X-ray diffraction of nylon [1], many fruitful studies have been presented using X-ray diffraction, infrared absorption and other techniques. It can be expected that solid-state NMR provides useful information about the structure and dynamics of the crystalline and noncrystalline components of polyamides [2, 3]. Actually, solid-state H, and NMR have been successfully used to clarify various crystalline and amorphous components. 

To elucidate the phase structure in detail it is necessary to characterize the molecular chain conformation and dynamics in each phase. However, it is rather difficult to obtain such molecular information, particularly of the noncrystalline component, because it is substantially amorphous. In early research in this field, broad-line H NMR analysis showed that linear polyethylene crystallized from the melt comprises three components with different molecular mobilities solid, liquid-like and intermediate molecular mobility [13-16]. The solid component was attributed to molecules in the crystalline region, the liquid component to... 

Rather recently, we have studied the solid-state structure of various polymers, such as polyethylene crystallized under different conditions [17-21], poly (tetramethylene oxide) [22], polyvinyl alcohol [23], isotactic and syndiotactic polypropylene [24,25],cellulose [26-30],and amylose [31] with solid-state high-resolution X3C NMR with supplementary use of other methods, such as X-ray diffraction and IR spectroscopy. Through these studies, the high resolution solid-state X3C NMR has proved very powerful for elucidating the solid-state structure of polymers in order of molecules, that is, in terms of molecular chain conformation and dynamics, not only on the crystalline component but also on the noncrystalline components via the chemical shift and magnetic relaxation. In this chapter we will review briefly these studies, focusing particular attention on the molecular chain conformation and dynamics in the crystalline-amorphous interfacial region. 

The half-width of the crystalline component line was estimated to be 18 Hz. This value reflects the very stable orthorhombic crystalline phase of this sample. The component line shape centered at 31.0 ppm represents the contribution from the amorphous phase in which the molecular conformations are changed rapidly over all permitted conformations. The relatively narrow line width estimated as 38 Hz is caused by the rapid molecular motion. The line centered at 31.3 ppm represents the noncrystalline phase in which the local molecular motion can occur in the same manner as in the amorphous phase (in Tic time frame), but a long-range molecular motion accompanying a conformational change related to a 10-20 methylene sequence is severely restricted. The wide line width as 85 Hz... 

Molecular Weight Dependence of Phase Structure. Similar line shape analysis was performed for samples with molecular weight over a very wide range that had been crystallized from the melt. In some samples, an additional crystalline line appears at 34.4 ppm which can be assigned to trans-trans methylene sequences in a monoclinic crystal form. Therefore the spectrum was analyzed in terms of four Lorentzian functions with different peak positions and line widths i.e. for two crystalline and two noncrystalline lines. Reasonable curve fitting was also obtained in these cases. The results are plotted by solid circles on the data of the broad-line H NMR in Fig. 3. The mass fractions of the crystalline, amorphous phases and the crystalline-amorphous interphase are in good accord with those of the broad, narrow, and intermediate components from the broad-line NMR analysis. 

To this end, we emphasize that the two phases assumed for the noncrystalline component are well-defined by the differences in T2c. In the crystalline-amorphous interphase, a long-ranged molecular motion accompanying the conformational change of ca. 10-20 carbon atoms is very slow or almost inhibited. In this phase the trans-trans conformation may be somewhat abundant but generally all permitted conformations are widely distributed. 

Spin-Lattice and Spin-Spin Relaxations. In order to determine the content of these crystalline and noncrystalline resonances, the longitudinal and transverse relaxations were examined in detail. It was first confirmed that the noncrystalline resonance of all samples is associated with Tic in an order of 0.45-0.57 s. Hence, the noncrystalline component of all samples comprises a monophase, in as much as judged only by Tic. However, it was found that the noncrystalline component of drawn samples generally comprises two phases with different T2C values amorphous and crystalline-amorphous interphases. The dried gel sample does not include rubbery amorphous material it comprises the crystalline and rigid noncrystalline components. However, the rubbery amorphous phase with T2C of 5.5 ms appears by annealing at 145 °C for 4 minutes. For the orthorhombic crystalline component, three different Tic values, that suggest the distribution of crystallite size, were recognized for each sample, as normal for crystalline polymers [17,54, 55]. The Tic and T2C of all samples examined are summerized in Table 6. 

The resonance lines at 72.9 and 28.3 ppm are assigned to the crystalline components of a- and 3-methylene carbons because of their longer Tic values. These crystalline resonance lines are associated with two T1C values of ca. 209 and 9-10 s. This shows that both methylene carbons possess two components with different Tic >s> but this will not be discussed further, since the existence of plural TiC s is a normal finding for crystalline polymers as discussed in previous sections. On the other hand, the resonance lines at 70.9 and 27.0 ppm recognized for a-and (3-methylene carbons are assignable to the noncrystalline component, because these chemical shifts are very close to those in the solution. These lines are associated with only one Tic of 0.15 or 0-14 s and two T2c values of 7.95 s and 0.099 ms, or 8.22 s and 0.099 ms, respectively for the a- and (3 -methylene carbons. This suggests that the noncrystalline component involves two components, both associated with a same Tic and different T2c Js. The noncrystalline component with a T2c of 7.95 or 8.22 ms is thought to form an amorphous phase and that with a T2C of 0.099 ms comprises a crystalline-amorphous interphase. In order to confirm this, we examined the elementary line shapes of each component and performed the line shape decomposition analysis of the equilibrium spectrum. 

Figure 22-(a) shows the DD/MAS spectrum in the resonance range of a-methyl-ene carbon at 0 °C. This spectrum represents the thermal equilibrium state of this sample, because it was obtained by a single pulse sequence with the repetition time of 600 s longer than 5 times the longest Tic in the system. The spectrum (b) is that of the crystalline component, which was obtained with use of Torchia s pulse sequence [53]. In the equilibrium spectrum, the noncrystalline contribution (amorphous plus interfacial) can be seen upfield to the crystalline component. Figure 23 shows the elementary line shapes of the amorphous and crystalline-amorphous interphases that comprise the noncrystalline resonance. 

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