Structure and optical properties of transparent polyamide 6 containing lithium bromide

Abstract

We investigated the effects of lithium bromide (LiBr) on the structure and properties of polyamide 6 (PA6). The strong iondipole interactions between lithium cations and the amide groups in PA6 greatly increased the glass transition temperature (T g ) and retarded the crystallization rate of PA6. As a result, compressionmolded PA6 blends were highly transparent and had high T g values. The rheological terminal region was obvious in the blends because the ion-dipole interactions weakened at high temperatures. This indicates that the melt processability was barely affected by LiBr. We also evaluated the optical anisotropy of the polymer to determine its suitability as a functional optical film. We found that hot-stretched blend films had large positive orientation birefringence with significantly weak wavelength dispersion, which can be attributed to the enhanced anisotropic polarizability of PA6. We also found that the stress-optical coefficient in the glassy region decreased with increasing LiBr content.

Moisture-sensitive smart hot-melt adhesive from polyamide 6

“…For the dry films immediately after compression molding, the peak temperature of E", defined as the glass transition temperature (T g ), was found to be 52 °C for pure PA6 and 90 °C for PA6/LiBr (90/10). This T g enhancement corresponds well with previous results and is attributed to ion-dipole interactions with lithium cations [4][5][6][7][8][9].…”

“…Furthermore, the peak at 983 cm −1 is known to be attributed to the amorphous band [15]. According to our previous study [4], LiBr addition reduced the crystallinity of both α-and γ-form crystals, as shown in Fig. 6a.…”

“…In our previous study, master curves of the oscillatory shear modulus were obtained as a function of frequency [4]. According to the experiments, the zero shear viscosities were 2.5 × 10 3 Pa•s for PA6 and 2.2 × 10 4 Pa•s for PA6/ LiBr (90/10) at 230 °C.…”

“…Recently, we found that adding LiBr greatly enhanced the glass transition temperature (T g ) of PA6 (48 °C for PA6 compared with 130 °C for PA6 containing 20% LiBr) [4]. Furthermore, the modulus in the glassy region was enhanced.…”

“…Moreover, adding LiBr reduces the crystallinity of PA6, leading to optical transparency. As the intrinsic birefringence is significantly high owing to enhanced polarizing anisotropy, ascribed to ion-dipole interactions [4,9], the hot-stretched film exhibits a high level of orientation birefringence.…”