Evaluation of Plastic Sheets and Films Measurement

Plastics are broadly classified into thermoplastics and thermosetting plastics, and thermoplastics are further classified based on mechanical strength and heat resistant properties. Aside from these thermal and mechanical properties are the optical properties of plastics that include haze, reflectance, and transmittance. Haze can be described as the proportion of diffuse transmittance to total transmittance, and is used to assess material surface treatment (matte and roughness). In addition, materials that are used for solar cells may have a periodic structure (textured structure) on their surface so as to increase dispersion and contain standard ISO 14782, whereas the same content is replicated in Japanese Industrial Standard (JIS) K 7136.^{1, 2)}

This article shows how Shimadzu UV-3600 Plus UVVIS-NIR spectrophotometer with ISR-1503 integrating light can be used to analyze plastics of different properties. International sphere attachment defines measuring the haze of plastic materials to determine their haze and solar transmittance.

ISR-1503 Optical System and Haze Measurement

The UV-3600 Plus UVVIS-NIR spectrophotometer is shown in Figure 1, and the ISR-1503 optical system is illustrated in Figure 2. The ISR-1503’s optical system is designed to facilitate horizontal sample placement when measuring transmittance/0-degree reflectance to enable measurement of film and tapered samples with no particular immobilization. The method used to measure diffuse transmittance and total transmittance is shown in Figure 3. These are properties used for calculating haze. Total transmittance is established by measuring both light transmitted directly through the sample and light diffused within the sample, while diffuse transmittance is ascertained by measuring only the diffuse light subsequent to removing the standard white board from the integrating sphere, as illustrated by the bottom image in Figure 3. It was observed that τ1 and τ2 in JIS K 7136 correspond to measured total transmittance^{Note 1} (τ1 being 100% transmittance with no sample placement), and τ3 and τ4 correspond to measured diffuse transmittance^{Note 1} (τ3 being nearly 0% transmittance with no sample placement). Haze is the ratio of diffuse transmittance to total transmittance, and can be measured using the following equation. Haze (%) = [ (τ4 / τ2) - τ3 (τ2 / τ1) ] × 100

Figure 1. UV-3600 Plus with ISR-1503 Installed

Figure 2. Left: Optical System of ISR-1503,
Right: Optical System of Conventional Integrating Sphere (Lateral View of Integrating Sphere)

Figure 3. Top: Total Transmittance Measurement (Corresponds to τ2 Measurement Method,
Bottom: Diffuse Transmittance Measurement (Corresponds to τ4 Measurement Method from JIS K 7136)

Sample Spectra Measurement

Shown in Figure 4 are plastics of different materials with different surface treatments that were examined. Samples No. 1 to 5 are sheets of about 3 mm thickness. Samples No. 1 to 3 are made of polymethyl methacrylate (PMMA), No. 2 has a matte treatment, No. 3 has a textured structure in a striped pattern, No. 4 is made from polyethylene terephthalate (PET), No. 5 is made from polyvinyl chloride (PVC), No. 6 and No. 7 are films of about 0.3 mm thickness and developed from PVC with a plasticizing agent additive (phthalate ester). No. 7 has been given a surface treatment. No. 8 and No.9 are films of about 0.03 mm thickness. No. 8 and No. 9 are made from polypropylene (PP) and polyethylene (PE), respectively. Samples were cut to sizes enabling their analysis with the ISR-1503 integrating light (maximum dimensions of W176 × D168 × T20 mm), and examined using the conditions shown in Table 1.

Figure 4. Plastics of Different Materials and Surface Treatments
1: PMMA (Clear), 2: PMMA (Matte), 3: PMMA (Textured), 4: PET,
5: PVC, 6: PVC (Clear), 7: PVC (Surface Treated), 8: PP, 9: PE

Table 1. Measurement Conditions

The total transmittance spectra and diffuse transmittance spectra of samples No. 1 to 3 are shown in Figure 5. Samples No. 1 to 3 are all made of PMMA. The total transmittance spectra show all samples with a transmittance of around 90% at long wavelengths more than 400 nm. The diffuse transmittance spectra show a transmittance of around 40% for the matte treatment sample (No. 2) and a transmittance of around 70% for the textured structure sample (No. 3). This highlights the surface treatment of samples results in light diffusion. Total transmittance spectra in the range of 200 to 2500 nm are shown in Figure 6. The results demonstrate that PMMA absorbed light at long wavelengths above 1000 nm. Samples No. 1 to 3 show absorption at nearly the same wavelengths as they are made of the same material.

Figure 5. Solid Lines: Total Transmittance,
Dotted Lines: Diffuse Transmittance (PMMA)
Black: No. 1 Clear, Red: No. 2 Matte, Blue: No. 3 Textured

Figure 6. Total Transmittance Spectra (PMMA)
Black: No. 1 Clear, Red: No. 2 Matte, Blue: No. 3 Textured

Shown in Figure 7 are the diffuse transmittance spectra and total transmittance spectra of samples No. 5 to 7. PVC is the key material used in samples No. 5 to 7. The total transmittance spectra indicate film samples with a transmittance of around 90% at long wavelengths above 400 nm. The sheet samples were found to absorb light at around 600 nm. The diffuse transmittance spectra show proof of light diffusion for surface treated sample No. 7, with a transmittance of around 40%. The total transmittance spectra in the range 200 to 2500 nm are shown in Figure 8. The results show that samples of the same material absorbed light at virtually identical wavelengths, and the degree of absorption varied based on the thickness of the sample.

Figure 7. Solid Line: Total Transmittance,
Dotted Line: Diffuse Transmittance (PVC)
Black: No. 5 Sheet, Red: No. 6 Film (Clear),
Blue: No. 7 Film (Surface Treated)

Figure 8. Total Transmittance (PVC)
Black: No. 5 Sheet, Red: No. 6 Film (Clear),
Blue: No. 7 Film (Processing)

The diffuse transmittance spectra and total transmittance spectra for samples No. 4, 8, and 9 are shown in Figure 9. The total transmittance spectra show all samples with a transmittance of around 90% at long wavelengths more than 400 nm. The spectra also show a transmittance of around 90% for thin film samples (No. 8 and 9) at wavelengths of 350 to 400 nm. In addition, the spectra show low diffuse transmittance for all samples. Total transmittance spectra in the range 200 to 2500 nm is illustrated in Figure 10. The results show that the material in sample No. 4 absorbed light at long wavelengths larger than 1000 nm, indicating that the thin film samples exhibited high transmittance at nearly all wavelengths

Figure 9. Solid Line: Total Transmittance,
Broken Line: Diffuse Transmittance
Black: No. 4 PET Sheet, Red: No. 8 PP Film,
Blue: No. 9 PE Film

Figure 10. Total Transmittance
Black: No. 4 PET Sheet, Red: No. 8 PP Film,
Blue: No. 9 PE Film

Table 2. Haze and Visible Light/Solar Transmittance

*1: Carboxylated, *2: Phthalic ester, *3: Values for reference only; JIS K 7136 applicable for measurement of samples with 40% or lower haze

Using color analysis software, τ1, τ2, τ3, and τ4 are calculated based on total/diffuse transmittance spectra. This software can output results in a wide range of formats, such as the XYZ color system, Munsell color system, and L*a*b* color system. τ1, τ2, τ3, and τ4 correspond to the Y value (color value) in the XYZ color system measured based on a D₆₅ standard illuminant. Table 2 shows haze results measured based on each τ value. The results show surface treated samples No. 2 and 7 with around 40% haze. The results also demonstrate a high haze for sample No. 3 with its textured structure. In sheet sample No. 5 PVC as well as in thin film samples No. 8 and 9, some haze was also measured. Table 2^{Note 2} also shows the visible light/solar transmittance results measured using solar transmittance software.

All samples, including those with surface treatment, exhibited visible light/solar transmittance of about 80 to 90%. It can be predicted that the degree of light diffusion changes without almost any change in sample luminosity.

Conclusion

Diffuse transmittance and total transmittance of various plastics were measured using Shimadzu UV3600 Plus with ISR-1503 attachment. Software and analytical results were also used to calculate Haze and visible light/solar transmittance of each sample. Haze, spectral, and visual light/solar transmittance measurement is anticipated to be applied to assess and validate the properties of ever more advanced products and materials in the future.

Note 1: JIS K 7136 assumes use of a single beam and for this reason requires a compensation port in the integrating sphere. The method used in this article is not entirely compliant with JIS K 7136, as the UV-3600 Plus uses a double beam and the ISR1503 has no compensation port. The assumption was made that these factors did not affect haze results.

Note 2: The solar transmittance software calculates solar transmittance in the range of 300 to 2100 nm. A user defined function allows solar transmittance to be calculated in the range of 300 to 2500 nm.

References and Further Reading

1. ISO 14782 Plastics — Determination of haze for transparent materials
2. K 7136 Plastics — Determination of haze for transparent materials

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.