UVA Effectiveness - Critical Wavelength

Similar to the Boots Star method, a sample is prepared according to a substrate technique, its spectral transmittance is measured, Tλ, and converted to spectral absorbance values Aλ = -log (Tλ). A ratio is calculated as follows which determines the total absorption in incremental wavelength bands and compares it to the total UV absorption. The ratio recorded for each wavelength, λ is:

(5)

The critical wavelength, λc, is the first value where the ratio R ≧ 0.9.

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Table 5- 4 Level of Protection (Critical Wavelength)[96]

λc Level of Protection

340nm≦λc＜370nm Some

λc＞370nm More (broad-spectrum)

5.3 Results and Discussion

It could be observed by the electronic microscope that, in Figure 5-2(a), the fiber diameter of PLLA was approximately 4.92 ± 2.23μm and on the surface of the fibers were pores at the size of around 10nm. In Figure 5-2(b), the fiber diameter of PLLA/0.3% Benzophenone-12 was approximately 3.56 ± 0.6μm and on the surface of the fibers were pores at the size of around 10nm. In Figure 5-2(c), the fiber diameter of PLLA/0.3% Chemfos-168 was approximately 1.25 ± 0.6μm and on the surface of the fibers were pores at the size of around 10nm.. In Figure 5-2(d), the fiber diameter of PLLA/0.3% Chemsorb-p was approximately 1.25 ± 0.6μm and on the surface of the fibers were pores at the size of around 10nm.

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Figure 5- 2: SEM Image (a) PLLA , (b) PLLA/Benzophenone-12 , (c) PLLA/Chemfos-168(d) PLLA/Chemsorb-p

In Figure 5-3(a), Micro-Raman spectra of PLLA fibers. (b), Micro-Raman spectra of PLLA/Benzophenone-12 fibers. (c), Micro-Raman spectra of PLLA/Chemfos-168 fibers. (d), Micro-Raman spectra of PLLA/ Chemsorb-p.

Micro-Raman Spectroscope is utilized to conduct fiber membrane analyses at CH3 and CH bending region. The CH3 asmmetric deformation modes appeared at about 1450±2cm^-1 as intense Raman and IR bands in all the compounds. The 1250-1400 cm^-1 region of the Raman spectra. Like in polypropylene and poly(α-L-alanine), this region was characterized by three groups of bounds at 1390, 1360 and 1300 cm^-1.C=O stretching region. Presents the 1650-1850 cm^-1 region of the Raman spectra. Raman spectra (800-950 cm^-1 region) of

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poly(L-lactic acid)s. Skeletal stretching and rCH3 rocking region. Figure 5-3 shows several strong absorption bands in the 1000-1250 cm^-1 region.

In Figure 5-3(b), Micro-Raman spectra of PLLA/Benzophenone-12 fibers.

BP crystallizes in two polymorphic forms with stable α-phase and metastable β-phase[67]. The deformation vibrations of the phenyl ring at 564, 625, 627 and 724 cm^-1 (measured: 565, 616, 619 and 723 cm^-1) and the out-of-plane C–H deformation vibration at 770 cm^-1 (measured: 768 cm^-1) are predicted quite correctly. The very intense lines at 1002 and 1029 cm^-1 in the experimental Raman spectra are predicted as the deformation vibration of the phenyl ring (1006 cm^-1) and as the C–C stretching vibration of the phenyl ring (1038 cm^-1).

Most likely, the deformation vibration at 1006 cm^-1 is appreciably affected by the phenyl ring C–C stretching vibrations leading to increase of its intensity. In such a case the mixed character of the 1006 cm^-1 vibration becomes apparent.

The next quite intense modes of the BP molecule appear to be the stretching CB–C–CA vibrations at 1154 and 1276 cm^-1 (measured: 1145–1166, and 1279 cm^-1). Some discrepancies between calculated and measured frequencies is seen in the spectra, however they are not too large. The most intensive lines in the experimental Raman spectra are at 1596, 1601 and 1650 cm^-1. Theoretical calculations predict these modes as corresponding to the phenyl ring C–C stretching vibrations (1594 and 1614 cm^-1) and to the C=O stretching vibration (1707 cm^-1). Whereas the intensities of these vibrations are predicted quite correctly, nevertheless, the large deviations between the measured and calculated frequencies are observed.

In Figure 5-3(c), Micro-Raman spectra of PLLA/ phosphite Chemfos-168 fibers. We initially chose to use Raman spectroscopy of the polymer film.

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Several absorption bands of 168 (1213, 1196, 1083, 854 and 776 cm^-1)[69-70]

are candidates for monitoring the 168 concentration as they are resolvable from the polymer. In practice the peak at 1083 cm^-1 was most clearly defined when analysing a Polymer film containing dissolved 168 and this peak was chosen for analysis.

In Figure 5-3(d), Micro-Raman spectra of PLLA/ Chemsorb-p. A strong deuteration effect is evident for the two lines at 1604 and 1422 cm^-1. The latter becomes a doublet on deuteration. The fundamentals at 1296 cm~1 collapse on deuteration and the 1342 cm^-1 fundamental band in the protonated molecule reveals a double-peak structure. Analogous to the situation for TIN, the spectra of HBT and HBO show strong effects on deuteration near 1600 cm^-1 with a large downshift of about 10 cm^-1. Around 1450 cm^-1, strong intensity redistribution occurs together with wavenumber shifts, indicating a strong alteration in the normal coordinate for the respective modes. Concentrating on deuteration effects on the skeletal vibrations of the molecules, we exclude the spectral region of the X-H stretching modes from our discussion. A characteristic phenolic OH stretching mode is observed in all three molecules, pointing to strong intramolecular hydrogen bonding in a non-polar solvent. It displays the large isoshifts of the respective band, characteristic of a localized mode. There is a simple physical explanation for the isoshift effects in the two modes which occur in all three molecules around 1600 and 1450 cm^-1. They derive their large Raman intensities from coupling of the phenolic C-O-H group to two spectrally neighbouring degenerate modes of the six-membered ring which is part of the phenolic group. Degeneracy is broken by either a stretching or a deformation of the C-O bond from the attached C-O-H group. In benzene, the E2g mode at

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1595 cm^-1 is strongly Raman active. The analogous mode for TIN lies at 1604 cm^-1. The degeneracy is broken by coupling of the C-O stretching coordinate.

The 1422 cm^-1 of TIN is connected with a C-O-H deformation movement coupled to the E1u mode, being at 1485 cm^-1 in benzene. The latter benzene mode is not Raman active by itself and the intensity comes from coupling to the remainder of the molecule. The essential downshift of δCOH on deuteration brings about a reorga- nization of the normal coordinates for the mode near 1422 cm^-1 and is connected with strong redistribution of intensities in the neighbouring bands. Raman excitation at the high-wavenumber side of the resonant molecular 0-0 transition results in the appearance of a distinct transition of TIN at 366.8 nm, a good-quality overtone spectrum was obtained.

The doublet found on deuteration around the 1422 cm^-1 mode is repeated in the combination tone spectrum. This holds for combinations with the 469 cm^-1 mode up to four orders.

Vibrational spectroscopy has been extensively used also for investigating the in vitro and in vivo degradation mechanism and kinetics of different biomedical devices composed of PLAs. The I875/I1452 Raman intensity ratio was utilized for a relative quantitative evaluation of polymeric chain length. The

I875/I1452 Raman intensity ratio was useful for studying the in vitro and in vivo

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degradation of PLA devices. The ratio was identified as a spectroscopic marker of the partial and progressive breakdown of the polymeric chain during degradation, spectroscopically confirming hydrolysis of ester linkage as the primary mechanism of PLA degradation.

As mentioned in previous literature, the I875/I1452 Raman intensity ratio signals results of bio-degradation and structural differences[77]. In this experiment, although both are bio-degradable membranes, the I875/I1452 Raman intensity ratio of PLA fiber membranes is 1.59; I875/I1452 Raman intensity ratio of PLLA/Benzophenone-12 fiber membranes is 0.61; I875/I1452 Raman intensity ratio of PLLA/Chemfos-168 fiber membranes is 1.53 while that of PLLA/Chemsorb-p fiber membranes is 0.43

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Figure 5- 3 Micro-Raman spectra of PLLA fibers, PLLA/Benzophenone-12 fibers, PLLA/Chemfos-168 fibers and PLLA/ Chemsorb-p fibers.

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In Figure 5-4 The PLLA, PLLA/ Benzophenone-12 and PLLA/

Chemfos-168 fibers were characterized by UV transmission. The characteristic UV transmission peaks from 200 to 400 nm wavelength. The PLLA/

Benzophenone-12 fibers has single sharp peak between 250 to 300 nm than other fibers. PLLA/ Benzophenone-12 has nano structure than PLLA and PLLA/ Chemfos-168 fibers.

Boots the Chemist, the largest producer of sunscreens in the UK, has developed a label system that uses a four star rating based on spectrophotometric analysis. The spectral transmittance values, Tλ, are converted to spectral absorbance values Aλ = -log(Tλ). A term called the UVA ratio is calculated which is the ratio of the total absorption in the UVA to that in the UVB (Eq 4,5) The method specifically calls for the Aλ data to be measured in 5 nm increments and for the integrals to be solved using Simpson‘s Rule for area approximation.

The limits of the UVA and UVB spectral regions also vary slightly from those previously noted. This sort of discrepancy for UVA and UVB is frequently encountered within scientific publications.The star rating, and its associated claim for UVA protection,is determined from the measured UVA ratio(Table 5-5)[96].

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Figure 5- 4 The transmission spectra of (A) PLA , (B) PLA/Benzophenone-12 , (C) PLA/ Chemfos-168 fibers.

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Table 5- 5 UVA Effectiveness - UPF and Critical Wavelength

The PLLA has a good ability in anti-ultraviolet. We use the elements (UV absorption and anti-oxidation agents) composite with PLLA by electrospinning in our study. We observed the PLLA/ UV absorption (Benzophenone-12) fiber membranes higher than PLLA membrane 14.9% in UVA ratio and PLLA/

anti-oxidation agents (Chemfos-168) fiber membranes higher than PLLA membrane 17.9% in UVA ratio. As mentioned in previous literature, the I875/I1452 Raman intensity ratio signals results of bio-degradation and structural differences. In this experiment, although both are bio-degradable membranes, the the PLLA/ UV absorption (Benzophenone-12) fiber membranes higher than PLLA membrane 61.6% in I875/I1452 Raman intensity ratio and PLLA/ anti-oxidation agents (Chemfos-168) fiber membranes higher than PLLA membrane 3.7% in I875/I1452 Raman intensity ratio. So PLLA Add UV absorption (Benzophenone-12) fiber membranes can achieve good UV resistance and fast bio-degradation.

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