| It is well known that polyimide possessed outstanding comprehensive properties especially the ultraviolet shielding capability because of the aromatic heterocyclic units in its molecule. However, the common polyimides are mostly insoluble or infusible thus difficult to process, and the resulted films are often in dark color, which extremely confines their applications in the field of radiation protection. In this paper, a soluble was synthesized and applied as ultraviolet resistant coating for poly(p-phenylene benzobisoxazole) (PBO) fiber and ink jet materials.The aromatic diamine,3,3',5,5'-tetramethyl-4,4'-diaminodiphenyl toluene was firstly synthesized from 2,6-dimethylaniline and benzaldehyde, and then polymerized with 3,3',4,4'-benzophenonetetracarboxylic dianhydride to produce the soluble polyimide (SPI) with relatively high molecular weight. SPI could be dissolved quickly in most polar organic solvents such as N-methyl pyrrolidone, dimethylacetamide, chloroform and carrene, and could be cast into films with light color and high transparence. It has been found SPI showed excellent ultraviolet shielding, good thermal stability, fine mechanical property and high surface free energy. Specifically, the yellowness index of SPI film was 5.62, the cutoff wavelength located at 380 nm and the optical transmissivity was greater than 82% after 480 nm. Meanwhile, the glass transition temperature of SPI film was higher than 400℃, and 10% weight loss temperatures in both air and nitrogen atmospheres were 462～465℃and 526～530℃respectively, moreover, the mass retention was 50%～54% under 900℃in nitrogen atmosphere. The intensity, the elongation at break, the modulus of SPI film were 87MPa,5.5% and 3.3GPa, and that the surface free energy a as well as its nonpolar componentσd and polar componentσp were 60.8,50.1 and 10.7, respectively. The results of rheological testing indicated that the SPI solution showed an Newtonian behavior, i.e., the viscosity depended mainly on the concentration and the temperature.PBO fibers were coated by using SPI solutions with different concentrations. The modified PBO (named xSPI/PBO, where x was the concentration of SPI solution with a mg/mL unit) fibers were found to have higher intensities compared to PBO fiber. For instance, the elongation intensity of 100SPI/PBO fiber was 37.18cn/dtex,28.12% higher than that of PBO fiber. The accelerated ultraviolet aging was carried out for the modified PBO fibers, and the mechanical property and intrinsic viscosity variations during the test were investigated. It was found that with the increasing coating thickness the elongation intensity and intrinsic viscosity retentions of SPI coated PBO fibers increased obviously compared with untreated PBO fiber. Especially, the 50SPI/PBO fiber, with a coating of suitable thickness, integrity and uniformity, gave higher intensity retention of 89.59% than that of 40.25% of PBO fiber, showing an effectively improved ultraviolet stability.SPI was also dissolved in m-cresol in different concentrations and the solutions were sprayed into the surface of ink-jetted color film to form a transparent uniform SPI coating. The influence of SPI coating on the photo stability of ink dye was investigated through the daylight ageing and accelerated ultraviolet aging measurements for the treated color films. It has been found the SPI coating could provide a fine protect for the ink dye, for example, the fading rate of red dye would decrease dramatically from 32.34% to 3.41% while the coating thickness was 2.0～2.3μm. From the integrations of uv-vis transmitted spectra of ink dyes during the aging process, both daylight and ultraviolet radiation could cause the fading of ink dye. However, the daylight effect would take effect only when the existence of oxygen, whereas the ultraviolet radiation was believed to be the major cause for the dye fading. |
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