Plastic and Polymer Thin Film Production Using Mini-Film Maker Accessory

IR spectroscopy or infrared spectroscopy is used for identifying a group of chemical species in a wide range of sample materials. This technique is mainly utilized for classifying organic chemical materials based on the number of carbon atoms present in the molecular structure. There are many polymeric and plastic-type samples that can be included in organic molecular materials and they can be divided into specific family groupings. The sample family types can be identified both quantitatively and qualitatively using the Attenuated Total Reflectance (ATR) method as an IR measurement.

ATR Technique

The ATR technique refers to the surface measurement of a sample type having a penetration depth of circa 2µm into the sample surface using a ZnSe or diamond crystal, rendering an effective pathlength measurement distance of circa 4.5µm for a reflection event of the sample area under analysis.

In an ATR measurement of a polymer and plastic-type sample, it is possible to ascertain the polymer family type but the sensitivity of the measurement for the effective pathlength allowed may not be adequate to measure any particular sample constituents, such as fillers and additives, in the make-up of the polymer material present in low concentrations. Hence, it may be important to produce a thin film of the polymer and plastic sample for transmission analysis from an appropriate film-making accessory.

Application

Using the Specac Mini-Film Maker Kit (p/n GS03970) (Figure 1), a thin film of the polymer/plastic sample is produced by melting or softening the sample at less than 250°C to set it on the equipment. Then, the pressing force against the molten plastic sample inside the filmmaker assembly of parts is applied using the dedicated press with 2 tons pressing capability in the complete kit. In case a thin film diameter of larger than 15mm is needed, Specac’s alternative filmmaker accessories can be used.

Figure 1. Specac’s Mini-Film Maker Kit (p/n GS03970)

The constant Thickness Film Maker Accessory (p/n GS15640) is utilized with the larger 15 ton Manual Hydraulic Press (p/n GS15011) equipped with Heated Platens (p/n GS15515), to facilitate the formation of polymer films up to a diameter of 29mm and at melt temperatures of up to 3000C. Likewise, the High-Temperature Film Maker Accessory (p/n GS15800) is also employed in a 15 ton Manual Hydraulic Press (p/n GS15011); however, this filmmaker has its own set of heated platen surfaces to create films up to 29mm in diameter at melt temperatures of up to 4000C.

Materials and Method

The Mini-Film Maker Kit (p/n GS03970) from Specac was utilized for thin-film preparation of a wide range of plastic/polymer sample types at a nominal film thickness of 50µm and a diameter of up to 15mm. The plastic/polymer material types were the same group of samples that had been detected for their polymer family types from the Quest ATR study.

Next, transmission spectra across the spectral range from 4000cm^-1 to 40cm^-1 for the nominal 50µm-thick film formed were obtained on a Thermo Nicolet iS5 instrument by means of the traditional room temperature detector system set at a 4cm^-1 resolution for 32 scans.

The samples utilized for this analysis are shown in the following images as to their form prior to creating them as 50µm-thick films (Figure 2).

Figure 2. Plastic/polymer sample types

Among the 13 different samples, 7 different basic polymer family types are present. For better identification, they have been color-coded as identical family types for their sample number as shown in Table 1. The sample types detected from the ATR measurement and utilized for formation into 50µm-films for transmission spectral measurement and collection are shown as follows.

Table 1. Sample number with descriptions and polymer sample type.

Samples 10 and 11 (cellophane chip and polystyrene tile, respectively), could not be formed into a thin film due to their original sample form and state. Only an ATR spectrum for spectral collection and data can be achieved for such sample types.

While producing thin films, it is necessary to define a method and specific process steps in the sample preparation so as to achieve the consistent results from spectral analysis. Important points for the methodology steps in sample preparation involve:

• The option of sizing ring to form the nominal film thickness
• Melting point temperature of the plastic/polymer sample material
• Quantity of sample utilized with a particular sizing ring
• Tonnage load applied when sample is melted and being pressed
• Duration of the tonnage load being applied
• Cooling downstage (is a load being applied) and when access can be gained to the film

For this analysis, steps 2 to 6 were maintained consistently for each type of sample. Table 2 shows the conditions for the procedural steps taken in the method.

Table 2. Conditions for the procedural steps taken in the method

(*) For the Cooling Down Stage step, specifically, when the 0.75 tons load being applied from the press was released at the melting point temperature, the filmmaker assembly of parts was removed from the press whilst hot and placed on the black colored cooling block disc of the kit of parts. Access to the film from peeling away the two aluminum foils was achieved when the film was near to room temperature conditions.

All prepared films were placed in a Specacard (p/n GS03800) to be positioned suitably within the IR spectrometer sample compartment for spectral collection. Then, each film when placing in a Specacard was determined for its thickness by means of a digital micrometer depth gauge. Table 3 shows the true film thicknesses determined for each sample.

Table 3. Actual film thicknesses measured for each sample

Spectral Data

Figures 3 to 11 show the transmission spectra collected for 11 samples prepared with the 50µm-thick sizing ring under the particular method and sample preparation procedural steps.

Figure 3. Sample 1 - Prepared as 50-micron thick film and run as FilmsamplelB

Figure 4. Sample 2 - Prepared as 50-micron thick film and run as Filmsample2B

Figure 5. Sample 3 - Prepared as 50-micron thick film and run as Filmsample3B

Figure 6. Sample 4 - Prepared as 50-micron thick film and run as Filmsample4B

Figure 7. Sample 5 - Prepared as 50-micron thick film and run as Filmsample5B

Figure 8. Sample 6 - Prepared as 50-micron thick film and run as Filmsample6B

Figure 9. Sample 7 - Prepared as 50-micron thick film and run as Filmsample7B

Figure 10. Sample 8 - Prepared as 50-micron thick film and run as Filmsample8B

Figure 11. Sample 9 - Prepared as 50-micron thick film and run as Filmsample9B

Figure 12. Sample 12 - Prepared as 50-micron thick film and run as Filmsample12B

Figure 13. Sample 13 - Prepared as 50-micron thick film and run as Filmsample13B

Discussion

Generally, the exact thickness of the film determined with the micrometer depth gauge correlates with the nominal thickness of a film that would be anticipated from a preparation using the 50µm-sizing ring. The 11 separate transmission spectra obtained for the plastic/polymer samples prepared as nominally 50µm -thick films indicate the family type of polymer material. The spectra representing the same family type of polymer material demonstrate them to be identical however, there are subtle features in each spectrum that make it possible to distinguish the specific sample from another sample type.

Among the five different polymer family sample types of spectra obtained, four can be compared from an overlay of their separate spectra. The sample spectra compared for their overlays are:

• Samples 1, 2 and 12 for a PVC family type polymer material
• Samples 3 and 9 for a polycarbonate family type polymer material
• Samples 4, 6 and 13 for a polypropylene family type polymer material
• Samples 7 and 8 for a polyethylene family type polymer material

The superimposed spectra have been shown between 3800cm^-1 to 500cm^-1 and have been completely scaled for the strongest absorbance peak in the spectrum.

Conclusion

The Mini-Film Maker Kit from Specac can be utilized for preparing thin films of up to 15mm in diameter and thicknesses ranging from 15 to 500µm for a wide range of plastic/polymer materials, provided that the melting point of the polymer is either below or does not surpass 250°C. The 50µm-thick films prepared for the plastic/polymer type were then examined to create an IR transmission spectrum which helps in identifying the polymer material from a family type classification. A good spectral agreement can be observed for peak positions with regard to the comparison of similar family type materials from an overlay of separate spectra created.

For polymeric sample types, complete resolution of spectral peaks, as well as measurable absorbance intensities, can be obtained using the ATR method rather than measurement by transmission. On the other hand, over-absorption of the strong bands in a transmission spectrum from the bulk of a polymeric material structure can be sacrificed for their positive status if it enables for the weaker band absorption intensities from low-level constituents. As a result, it would be important to create a uniform and consistent thin film from a plastic/polymeric sample for determining low-concentration constituents that cannot be consistently calculated from a short pathlength and surface measurement method and therefore the Mini-Film Maker Kit is suitable for thin-film production.

This information has been sourced, reviewed and adapted from materials provided by Specac.

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