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Article

The Efficiency Evaluation of the Reactive Extrusion Process for Polyethylene Terephthalate (PET). Monitoring of the Industrial Foil Manufacturing Process by In-Line Rheological Measurements

by
Piotr Szymczak
1,2,*,
Damian Dziadowiec
1,2,
Jacek Andrzejewski
1,* and
Marek Szostak
1
1
Institute of Materials Technology, Faculty of Mechanical Engineering, Poznan University of Technology, ul. Piotrowo 3, 61-138 Poznan, Poland
2
EUROCAST Sp. z o.o., Wejherowska 9 Str., 84-220 Strzebielino, Poland
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2023, 13(6), 3434; https://doi.org/10.3390/app13063434
Submission received: 13 February 2023 / Revised: 3 March 2023 / Accepted: 6 March 2023 / Published: 8 March 2023
(This article belongs to the Section Green Sustainable Science and Technology)
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Abstract

:

Featured Application

Foil extrusion processing, recycling of waste origin plastics, viscosity monitoring.

Abstract

The main topic of the presented work is the evaluation of the in-line viscometer (VIS) operation installed on the industrial line for polyethylene terephthalate (PET) foil production. The tests were performed during the regular operation of the machine, which results from the need to maintain production continuity. Polymer viscosity control is of particular importance in the production of degradable materials and recycled polymers. The processing of PET film is, therefore, a particularly difficult issue due to the presence of both of these problems at the same time. The conducted research had a two-pronged character: assessment of the correct operation of the viscosity measurement system and testing of the effectiveness of reactive additives during the extrusion process. Measurements were carried out with the use of several types of input materials, including recycled blends. The key tests were carried out with the addition of viscosity modifiers. Measurements conducted during the extrusion process confirmed the effectiveness and high sensitivity of the in-line system (VIS), while clear changes in the polymer flow characteristics were observed only after the addition of chain extenders. The in-line measurements revealed that the addition of 1% of the reactive compound increased the viscosity from the initial 150 Pa∙s to over 350 Pa∙s. The most significant increase in viscosity for the additive based on pyromellitic dianhydride (PMDA) confirms the effectiveness of the reactive extrusion method and the suitability of the used measuring. During further analysis, the obtained films were also tested. The results showed no negative effects of the reactive extrusion on the mechanical performance of the foil; however, for recycled materials, the average values of tensile strength and elongation at break have deteriorated. A positive aspect of the use of reactive additives was the greater uniformity of mechanical properties. For some materials, there was a significant increase in the haze factor (transparency), which should be considered a disadvantage.

1. Introduction

The use of in-line rheological measurement methods during the processing of thermoplastic materials has been the subject of scientific research for a long time [1,2,3]. The rheological characteristics of molten polymers, which can be measured by conventional off-line techniques [4,5], are usually not the same as the properties of these materials in the actual process, such as extrusion or injection molding [6,7]. The main problem here is the high shear forces to which the polymers are subjected during the flow. With many standard devices used to determine viscosity, such as rotational and capillary rheometers, it is difficult to achieve actual process conditions [8,9].
The subject of research concerning attempts to reflect the shear conditions prevailing during extrusion was the subject of many studies; in this case, most of the works are based on the analysis of measurement results on capillary rheometers [10,11]. A more complicated issue is the attempt to carry out similar measurements during injection molding, which results from much higher shear forces [12,13,14]. However, attempts to simulate the conditions of technological processes in off-line measurements will never allow reflection of the influence of the entire process on the properties of the material. It is difficult to take into account the residence time of the material, changes in the geometry of processing tools, or other conditions specific to a given type of manufacturing technique during a standardized test. The demand for in-line measurements is particularly important during the manufacturing of thermal/shear-sensitive materials since the rheological characteristic of the raw material supplied to the technological process strongly differs from the properties of the samples taken after the extrusion/injection step.
In the case of plastics processing, the need for measurements may turn out to be useful in controlling the properties of multi-component compositions, such as polyvinyl chloride (PVC) blends, or processes based on materials with unstable properties, such as recycled plastics. The PET foil extrusion process discussed in this article is an example of using post-consumer materials. Despite advanced purification processes, the material charge may turn out to be less valuable due to its origin. The most common form of recycled PET is shredded flakes. This type of material might consist of bottles or thermoformed containers, which means that a large share of the input material might be already been processed several times. Each subsequent processing significantly affects the key rheological parameter of PET, which is the intrinsic viscosity (IV). Although for cast film extrusion, the tolerance of the IV range is relatively wide, usually from 0.7 to 1.0 dL/g, while for PET bottles is 0.78–0.85 dL/g [15,16,17], the changes in viscosity during a large-scale process may affect numerous functional properties of the foil, such as strength, thickness, transparency. Among the many methods of improving the viscosity of PET, the techniques of reactive extrusion are currently gaining popularity, where a polymer material with low viscosity is subjected to a chain extension reaction in the melt phase on an extruder. It allows for significant cost savings compared to methods such as solid-state condensation [18]. In the case of reactive extrusion of thermoplastic polyesters, numerous chemical compounds turn out to be effective [19,20,21,22], but due to the high sensitivity of the reactions to thermal conditions, this process often requires optimization. For the presented study, the main reactive compound was pyromellitic dianhydride (PMDA), the effectiveness of which has been confirmed for many processing techniques [23,24,25,26].
The in-line viscosimeter (VIS system) that was used for the conducted study was working together with the gear pump that creates a defined volumetric polymer flow from the main melt channel of the extrusion system to a slit capillary which has a defined geometry. The pressure transducers measure the differential pressure in the capillary. The higher the differential pressure, the higher the viscosity. Although systems of this type are an excellent tool for controlling viscosity changes, however, taking into account that viscosity measurement for viscoelastic liquids requires the use of numerous conversion calculations, the so-called rheological corrections, measurements during the actual production process do not give such accuracy as the results from the capillary rheometer. In the case of polymer flow measurements, several basic conversion factors are used: Weissenberg–Rabinowitsch correction for non-parabolic velocity profile [2,27,28]; Bagley Correction—for inlet and outlet pressure loss [12,29,30,31]; Mooney correction—for wall slip in the capillary [32,33]. The problem with using this type of calculation is the need to perform several preliminary measurements at different shear rates, often also for different capillary geometries. In the case of in-line measurements, such tests are impossible to perform because the geometry of the measuring channel is constant, and the measurement itself is usually carried out at a constant shear rate.
The present study discusses the results of industrial tests of the in-line rheological measurement system. The properties of materials obtained during the technological tests have been subjected to mechanical tests, transparency analysis (haze test), and differential scanning calorimetry (DSC) thermal analysis.

2. Experimental

2.1. Materials

The extrusion tests were carried out with the use of two types of viscosity modifiers. The materials used in the form of commercially available granules are certified for use in the production of food-grade film, which is crucial in the case of tests carried out on the particular extrusion line. The first modifier was Masspet 287R2 (Point Plastics SRL, Colleferro, Italy), where the reactive agent was pyromellitic dianhydride (PMDA) at the concentration of 13%, and the pellets were prepared on the PET-based carrier. The second type of modifier was Belar MBRT900F (Belar SRL, Cairo Montenotte, Italy); the exact characteristics of this additive have not been disclosed by the manufacturer; therefore, we treat this material as a comparative sample. During the research work, viscosity modifiers were used in the amount of 1%; therefore, for samples subjected to the reactive extrusion process, additional designations B1 and M1 were used, respectively, for the Belar and Masspet compounds.
The manufactured three-layer film was prepared in the ABA system; the composition of the outer layer (A) was always the same, while the composition of the core of the produced film was modified. The outer layer (A) is made of pure PET of the RAMAPET N1 type (Indorama Ventures Poland, Wloclawek, Poland), with the addition of 1% slip/anti-blocking masterbatch Luvobatch PET SA/AB 5501 (Lehmann&Voss&Co., Hamburg, Germany).
The core layer modification is the main object of experiments; in the case of the discussed study, three different types of matrix compositions were used. The base material was unprocessed PET pellets of the Neopet 80 type (NeoGroup, Vilnius, Lithuania); according to the technical datasheet, this resin type consists of PET copolymer and is intended for the production of food packaging applications. Further in the text, this material is marked as virgin PET (V) and virgin-dried PET (VD) for samples subjected to additional drying procedures. The second type of modified composition was a recycled PET blend designated as MIX. This system consisted of a mixture of PET flake (PET 9000 Clear from Indorama Ventures Poland) and ground bottle preforms (from AlphaPlast, Leopoldhohe, Germany), and the share of both components was 50/50%. As the main component of the foil is the core layer, further designations regarding the foil will refer to the composition of the foil core layer (B).

2.2. Sample Preparation

The film production line consists of a dosing system, two extruders, a feedblock, a die-head, a calendering section, and a receiving and winding system. The dosing system feeds the raw material to the extruder. The installation includes two extruders, both produced by the company Construzioni Meccaniche Luigi Bandera S.p.A. (Busto Arsizio, Italy). Extruder A was a single-screw machine equipped with a 50 mm diameter screw, L/d = 30. Extruder B was the twin-crew machine, screw diameter of 85 mm, L/d = 52. In extruder B, the material forming the main core of the foil is melted and homogenized, while extruder A forms the film side layer. From the extruders, the material is fed to the feedblock, which allows for obtaining a film with an ABA structure. In the feed block, the material from extruder A can be separated into two side layers, e.g., 5% each, then a film with the ABA structure is obtained. The material from extruder B makes up 90% of the product volume. The width of the head is 1300 mm, while the extrusion capacity of the entire line is up to 800 kg/h. The molten feedblock material is fed to the head, and through the slot, it is poured onto a heated drum (calender), where a polyester film is formed. The film is cooled as it passes through the calenders and then fed through a system of rollers to the winder. The edges of the foil are cut between the calender and the winding system. The waste material obtained after trimming the edges of the foil is ground and recycled as a raw material for the production of foil. It is important that for the purpose of the study, the line was equipped with the additional plastic viscosity measurement system located at the extruder B outlet. The scheme presenting the essential component of the extrusion line is shown in Figure 1.
Technological tests of PET modification with the use of viscosity modifiers were made during the regular operation of the extrusion line. Therefore the test procedure was carried out so as not to disturb the normal production schedule.
Table 1 presents a list of materials produced during the test procedure; the order of materials on the list corresponds to the order in which the material is introduced into the process. The working time of the line on individual materials was not the same, but each time it was about 60–100 min; in the case of two types of materials with the addition of the M1 compound, the time was reduced to around 20 min, due to the recorded high viscosities and the risk of damage to the loaded machine components.

2.3. Methods

In-line rheological measurements were carried out with the use of an industrial VIS Online Viscometer (Gneuss GmbH, Bad Oeynhausen, Germany). This type of device is installed downstream of the main extruder channel. The stream of polymeric material is thus taken directly from the stream of material being processed. In order to ensure a constant circulation of the molten polymer, the viscometer is equipped with a gear pump. Viscosity is measured while flowing through a measuring capillary equipped with two pressure sensors. All functional elements of the viscometer are heated, and additionally, the device enables direct measurement of the temperature of the flowing polymer. This type of system can be mounted on a machine of any size; additionally, it does not cause material losses. During the discussed tests, the temperature of the heating elements was 285 °C. For the whole experiment, the rheometer worked with a constant shear rate of 100 1/s.
Film properties were measured during the static tensile test with the use of the universal testing machine (Instron, Norwood, MA, USA); the machine was equipped with a 2000 N load cell. Tests were performed in accordance with ISO 527-3 standard using 15 mm wide strip samples.
Transparency measurement was carried out by haze tests, where foil samples were measured per the ISO 14782 standard.
The differential scanning calorimetry measurements (DSC) were conducted using Phoenix DSC 204 F1 machine (Netzsch GmbH, Selb, Germany). The tests were conducted using standard 1st heating/cooling/2nd heating procedure, where the heating cooling rate was set to 10 °C/min. The measurements were performed from 30 °C to 300 °C. The samples were prepared from small pieces of foil; the average weight of a single specimen was around 5 mg. The weighed samples were placed inside the sealed aluminum crucible; the lid was pierced for ventilation purposes. During the study, the oven chamber was purged with nitrogen. The crystallinity level was calculated according to the following Formula (1):
%   C r y s t a l l i n i t y = X c = 100 × Δ H m − Δ H c Δ H 100   ( 1 − φ )
where ∆Hm is the measured melting enthalpy, ∆Hcc is the measured enthalpy of cold crystallization, and ΔH100 is the theoretical melting enthalpy, φ refers to the filler/additive content. The melting enthalpy for the 100% crystalline PET phase was taken from the previous literature [34,35,36]. The research methodology of the presented study is shown in Figure 2.

3. Results and Discussion

3.1. In-Line Rheological Tests—Viscosity Difference for Standard and Reactive Extrusion

The results of in-line rheological measurements are presented in the form of a graph of viscosity change over time, measured during the production cycle lasting several hours (see Figure 3A). The reaction scheme of the PET chain elongation is presented in Figure 3B.
As can be concluded during a cursory analysis, the values of viscosity change during the process and may fluctuate significantly. This is especially true of the two areas of the graph which characterize the viscosity jump following the addition of the M1 compound in step no. 3 and no. 6. In both cases, where virgin type PET was processed (V and VD), the addition of the M1 chain extender resulted in a sudden increase in viscosity up to 380 Pa·s. In these two cases, the feeding time of the material containing the M1 (PMDA) modifier was limited to about 20 min, preventing further increase in the viscosity of the polymer. In addition to the two listed examples, for the remaining materials, the viscosity measurements show only a slight variation in flow characteristics.
Starting from stage No. 1, where the VD material was processed, the addition of the B1 modifier did not change properties much. The viscosity values recorded by the VIS viscometer changed from 150 Pa·s for the VD sample to around 200 Pa·s for VD-B1 materials. It is worth mentioning that the viscosity fluctuations during measurements for individual materials are also significant and can reach even ±15 Pa·s. In the next step, no. 3, a sharp increase in viscosity can be observed for the VD-M1 sample. After the viscosity exceeded the value of 350 Pa·s, there was another change in the composition of the charge material to undried virgin PET (V). The change of material allowed to quickly reduce the viscosity and stabilize its value again at the level of about 200 Pa·S; this value remained despite the addition of B1 in the step no. 5. Changing the composition in step no. 6 to V-M1 repeated the situation with a sharp increase in viscosity. Again, the material composition was changed after exceeding the viscosity reading of 350 Pa·s. The material processed at stage no. 7 consists of the recycled PET flakes/preforms with PMDA agent addition (MIX-M1). Again, changing the material composition caused the viscosity to drop, and it stabilized at about 180 Pa·s; however, this time, the main factor changing the polymer characteristics was the replacement of the virgin PET resin with a recycled mixture; therefore, as can be concluded, the efficiency of M1 modifier (PMDA) in such blends is lower than for unprocessed PET. A further change of the composition in step no. 8 to the MIX-B1 material does not bring any visible changes in viscosity, while for the unmodified batch extruded in the last step no. 9, a reduction in viscosity to the level of about 130 Pas is noticed.
Taking into account the obtained results, it should be stated that for virgin materials, the effectiveness of modifier B1 is negligible, while the addition of M1 is characterized by the very high efficiency of the PET chain extension reaction. The presumed course of the reaction between the polymer chains of PET and the addition of M1 (PMDA) is presented in Figure 3B. For this type of reactive extrusion process; it is possible to obtain different efficiency, where a single PMDA molecule can connect from two to four PET chains with each other. The intensity of this reaction depends mainly on the residence time of the material in the extruder system, where a more extended time period increases the probability of bond formation [26,37]. The results for recycled mixtures (MIX) are not so unambiguous; however, after the addition of both modifiers, the recorded viscosity values are higher than for the standard non-reactive process.

3.2. The Properties of the Manufactured Foil

The results of the mechanical tests are shown in Figure 4, where the charts present the values of the tensile strength (Figure 4A) and elongation at break (Figure 4B). The results include measurements performed in the machine direction (MD) and transverse direction (TD). In addition to samples prepared as part of the conducted experiment, the results also include measurements for reference materials, where APET (amorphous polyethylene terephthalate) refers to monolayer PET film, while PET/PE was prepared with an additional laminated polyethylene (PE) layer. Further, Figure 4C shows the results of haze factor measurements and the appearance of foil samples.
The preliminary comparison shows no correlation between the results of rheological and mechanical measurements; the increased viscosity of VD-M1 and V-M1 materials does not translate into changes in the strength or elongation of foil samples. APET monolayer foil can be treated as the basic reference material. The APET film strength of 45 MPa was obtained for only two materials prepared during the conducted tests, V and VD-M1 foil. However, it is difficult to draw any more profound conclusions from this fact because the comparative analysis does not indicate any clear trends resulting from using the modifiers (M1/B1) or a different type of PET charge. Some indicators of worse properties may be low strength values for samples based on a mixture of PET flakes and preforms (MIX), but the results of elongation measurements do not confirm this.
As an example of a certain tendency, the properties of the film based on the VD (dried virgin PET) material can be considered, whereas, for the VD-M1 material, a visible increase in tensile strength by about 20% and elongation by about 15% can be observed. It is worth mentioning that for this group of materials (VD) the test results in both measured directions MD and TD are very similar, which in the case of other materials is not a rule. An example of that is the results for undried materials (V), where the strength for the MD direction for samples V and V-M1 is similar (about 40 MPa), while for the same pair in the TD direction, the values are strongly different, 54 MPa and 39 MPa, respectively, for V and V-M1. In this case, the measurements indicate the adverse effect of chain extenders on tensile strength, but the analysis of the elongation at break shows completely different conclusions. For the V sample, some attention should be paid to the significant difference in elongation for the unmodified sample, where the MD direction was 585% and for the TD only 9%. After the addition of the modifiers, the differences for the MD and TD directions became negligible, additionally, the average elongation was improved. For the sample V-B1 up to 780% and for V-M1 even 880%. The analysis of the results for the mixture of preforms and flakes (MIX) shows no visible trends, which is not surprising to some extent because as a product processed from the waste form of PET, this material is assumed to be significant. The results of tensile strength measurements for this group of samples show slightly lower values than for VD and V-type foils, while elongation measurements suggest relatively good material properties because the results for all measurements were within the range of 600 to 850%.
Taking into account the ambiguous changes in the properties of the PET film after the addition of chain extenders, it is worth noting that the positive aspect of using the reactive extrusion technique is the improvement of the uniformity of mechanical properties for the tested MD and TD directions. In the case of the discussed products, the level of film orientation was low; however, for the technology of producing BOPET (bi-oriented PET) films, this issue may be a key aspect of the reactive compounds application.
Analyzing haze measurements (see Figure 4C) brings unexpected results. For most of the prepared samples, the haze parameter, which is an indirect measure of foil transparency, does not exceed 2%, which proves good optical properties. It is worth mentioning that for the reference APET film, the haze parameter was the lowest (about 1%), which results mainly from the homogeneous nature of the material forming the cross-section of the film. Considering the issue of materials homogeneity, it is not surprising that the haze value is slightly higher for the film made of PET/PE laminate (≈12%). The reduced transparency is mainly influenced by the addition of PE and an adhesive layer. PE, as a polymer with a higher level of crystallinity itself, has an increased haze index; additionally, the transparency is influenced by the differences in the refraction angle for the PET core, the adhesive, and the PE layer. On the other hand, the results of measurements for materials with the addition of the M1 modifier are less expected. It is visible that each use of PMDA in the process increases the haze parameter, even up to 50%, as for the MIX-M1 sample. Such a significant change is difficult to explain, given the relatively low content of the modifier. Even for materials containing the addition of fillers or recycled resin [38,39], the transparency did not deteriorate in this way; hence there is no clear cause for the increase in the haze factor of the manufactured foils. Due to its multifactorial nature, this issue will be analyzed in more detail in further research.
Due to the fact that PET belongs to the group of semi-crystalline polymers, in many cases, its properties depend on the morphology of the crystalline phase, despite the fact that the crystallinity level for most of the foil did not exceed a few percent. The DSC analysis used for the evaluation of the crystallinity level is also helpful for a more deep understanding of the polymer phase transition differences. For the purpose of the study, the obtained results are presented in the form of DSC signal plots, while the crystallinity level is presented in a separate graph (see Figure 5). The individual figures present the comparison of the DSC plots of the 1st heating, cooling, and 2nd heating measurements. Additionally, Table 2 contains some of the basic thermal properties read from the DSC plots.
The appearance of 1st heating thermograms indicates some typical thermal properties of thermoplastic polyester. For all of the tested samples, the glass transition range, visible as a slight change in the baseline level, was very close to 75 °C. That is a typical value for pure PET resin since many other studies indicate similar results [26,40,41]. Another important feature visible on the DSC curve is reflected by a clear exothermic peak around 130 °C. That behavior is correlated with the cold crystallization phenomenon. The appearance of the visible peaks and the area of the transition (enthalpy) suggest the dominant amorphous nature of the prepared materials. For all tested samples, the maximum temperature (Tcc) and the peak area (ΔH) are very similar; hence again, it is difficult to find any differences for individual materials. The lack of significant differences in the appearance of DSC thermographs was also visible for the melting range. The enthalpy values obtained from the cold crystallization and melting were used for evaluation of the crystallinity level, which results are shown in Table 2.
According to the calculations, the content of the crystalline phase varies from 11% to 13%. This range is typical for fast-cooled PET resin, which was confirmed by other studies [35,42,43]. However, it should be pointed out that, again none of the results indicate any significant structural differences that could be caused by the used additives. Undoubtedly, this is a situation confirming that the characteristics of the extruder foils, including its structural properties, have not changed significantly after the reactive extrusion process. However, previously observed changes in the haze parameter for samples with the addition of PMDA are usually associated with changes in the morphology of the crystalline phase, which should be visible in DSC studies [39,44].
The lack of significant differences in the results for the materials subjected to DSC analysis does not always mean that the structural changes are not present. In many cases, the changes in the signal characteristics overlap, which means that the information on the DSC curve, important from the point of view of analysis, coincides with the signal for a more pronounced transition. In particular, this problem is important for the results of the 1st stage of heating, when the thermo-mechanical history of the sample has a great influence on the course of the DSC signals. After remelting, the cooling stage of the DSC test revealed more pronounced differences in thermal characteristics, especially for PMDA-modified samples. The discussed change concerns the visible shift in the exothermic peak position. For reference PET sample (VD) the crystallization peak maximum was at around 181 °C, while for most samples, it ranges between 183 °C and 190 °C. The observed increase can be related to a small nucleation effect, which is usually the case with even a small amount of additives or impurities [35]. A more interesting change was observed for PMDA-modified samples, where the crystallization exotherm was shifted to lower temperatures. Regardless of the used matrix, a drop in the crystallization temperature of about 10 °C was observed for all samples. This phenomenon appears to be related to the efficiency of the reactive extrusion process. The correlation of the efficiency of the reactive extrusion process with the phase transition change during crystallization has already been thoroughly described in other articles, in particular for chain extenders based on epoxy groups [45,46,47,48]. In the discussed case, the result indicates a very similar mechanism, where as a result of the addition of PDMA, the molecular weight of the processed PET increases, resulting in a change in the mobility of macromolecules and a reduction in the kinetics of the formation of lamellar structures of the crystalline phase [49]. Interestingly, in contrast to the results of the 1st heating phase, where the plot appearance suggests a lack of phase transition differences, the 2nd heating stage reveals a slight trend noticeable for samples with the addition of the PDMA (M1) modifier. In the discussed case, the trend concerns the appearance of an additional melting peak at around 235 °C, which is the result of the appearance of secondary crystal structures with lower lamellae thickness. As reported by other studies, the appearance of a double peak is induced by the chain extender addition. Due to the increase in molecular weight, the formation of crystal structures is limited, hence the formation of not fully developed subsidiary crystals [46,49].
In summary, it should be clearly indicated that further work in this area is necessary; however, the presented research clearly shows the effectiveness of the in-line technique in detecting changes in the viscosity of the processed PET material. Further work may help develop effective methods of detecting unexpected changes in the viscosity of the plastic, reducing the number of defective products.

4. Conclusions

The presented research was aimed at checking the concept of research work in the area of industrial scale measurements, where, due to the need to maintain production continuity, some aspects of the standard research methodology have been subordinated to the production methodology. Several main conclusions from the research can be formulated in the form of sub-points.
-
It can be stated with satisfaction that the observed results confirm the effectiveness of the in-line system in detecting changes in PET viscosity. The recorded changes in rheological characteristics result from the use of various types of material composition, including reactive additives increasing the composition IV coefficient.
-
The research shows that the effectiveness of many commercial additives of this type is questionable; they have low efficiency or require an optimization process, which would be problematic and costly to carry out on a high-performance industrial line.
-
The comparative analysis of the key tensile properties did not show any significant changes in the film performance, which can be considered a positive result.
-
In the case of the most efficient M1 compound, there is a significant drop in transparency (haze). It does not eliminate this type of product from use; however, to some extent, it limits the applications.

Author Contributions

Conceptualization, P.S., J.A., and M.S.; methodology, P.S.; software, P.S.; validation, J.A.; formal analysis, P.S. and D.D.; investigation, P.S. and D.D.; resources, P.S. and J.A.; data curation, J.A.; writing—original draft preparation, P.S., D.D., and J.A.; writing—review and editing, P.S. and J.A.; visualization, J.A.; supervision, J.A. and M.S.; project administration, P.S. and M.S.; funding acquisition, M.S. All authors have read and agreed to the published version of the manuscript.

Funding

The authors would like to thank the Ministry of Education and Science for funding the research under the Applied Doctorate Program in the years 2020–2024 (Agreement no. DWD/4/22/2020).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 13 03434 g001 550
Figure 1. The workflow diagram of the extrusion line operation intended for the production of ABA foils.
Figure 1. The workflow diagram of the extrusion line operation intended for the production of ABA foils.
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Applsci 13 03434 g002 550
Figure 2. The flow chart of the research methodology.
Figure 2. The flow chart of the research methodology.
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Figure 3. (A) The results of the in-line viscosity measurements conducted during the production of the PET foil. (B) Possible course of the reaction in compositions containing the addition of the modifier M1 (PMDA) to PET resin.
Figure 3. (A) The results of the in-line viscosity measurements conducted during the production of the PET foil. (B) Possible course of the reaction in compositions containing the addition of the modifier M1 (PMDA) to PET resin.
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Applsci 13 03434 g004 550
Figure 4. The results of the mechanical properties measurements obtained during the tensile test. (A) Tensile strength, (B) elongation at break. (C) The results of haze factor measurements and appearance of foil samples.
Figure 4. The results of the mechanical properties measurements obtained during the tensile test. (A) Tensile strength, (B) elongation at break. (C) The results of haze factor measurements and appearance of foil samples.
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Figure 5. The results of the DSC analysis for prepared foil samples recorded at subsequent measurement steps: (A) 1st heating, (B) cooling, (C) 2nd heating. (D) The results of the crystallinity calculations from 1st and 2nd heating stages.
Figure 5. The results of the DSC analysis for prepared foil samples recorded at subsequent measurement steps: (A) 1st heating, (B) cooling, (C) 2nd heating. (D) The results of the crystallinity calculations from 1st and 2nd heating stages.
Applsci 13 03434 g005
Table
Table 1. The list of samples prepared during the study.
Table 1. The list of samples prepared during the study.
MaterialVirgin PET (V)
(%)		Recycled PET (MIX)
(%)		IV ModifiersThickness
(µm)
MassPET (M)Belar (B)
VD *100---400
VD-B199- 1400
VD-M199-1-400
V100---400
V-B199--1400
V-M199-1-400
MIX-M1-991-400
MIX-B1-99-1400
MIX-100--400
Reference materials
APETMono film prepared from 100% amorphous PET resin250
PET/PEPET foil laminated on both sides with PE foil250
* The letter D indicates the materials that have been dried.
Table
Table 2. The thermal properties obtained from the DSC plot analysis.
Table 2. The thermal properties obtained from the DSC plot analysis.
SamplePeak Position
(°C)		Enthalpy, ΔH
(J/g)		Crystallinity (Content) *
(%)		Crystallization
Peak
(°C)
Cold Cryst.Melting Cold Cryst.Melting
VD 137.7251.833.949.511.1 (31.8)180.8
VD-B1132.0250.434.150.811.9 (32.8)183.5
VD-M1129.6250.529.445.411.4 (28.2)169.9
V131.3253.230.448.713.0 (27.4)183.9
V-B1128.9248.330.846.411.2 (27.3)187.3
V-M1133.0250.331.147.211.5 (28.0)172.6
MIX130.7253.132.149.812.7 (28.3)188.4
MIX-B1130.0252.731.748.011.7 (28.7)190.1
MIX-M1128.5250.830.347.212.0 (27.8)168.1
* The values in the brackets are calculated from the 2nd heating stage.
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Szymczak, P.; Dziadowiec, D.; Andrzejewski, J.; Szostak, M. The Efficiency Evaluation of the Reactive Extrusion Process for Polyethylene Terephthalate (PET). Monitoring of the Industrial Foil Manufacturing Process by In-Line Rheological Measurements. Appl. Sci. 2023, 13, 3434. https://doi.org/10.3390/app13063434

AMA Style

Szymczak P, Dziadowiec D, Andrzejewski J, Szostak M. The Efficiency Evaluation of the Reactive Extrusion Process for Polyethylene Terephthalate (PET). Monitoring of the Industrial Foil Manufacturing Process by In-Line Rheological Measurements. Applied Sciences. 2023; 13(6):3434. https://doi.org/10.3390/app13063434

Chicago/Turabian Style

Szymczak, Piotr, Damian Dziadowiec, Jacek Andrzejewski, and Marek Szostak. 2023. "The Efficiency Evaluation of the Reactive Extrusion Process for Polyethylene Terephthalate (PET). Monitoring of the Industrial Foil Manufacturing Process by In-Line Rheological Measurements" Applied Sciences 13, no. 6: 3434. https://doi.org/10.3390/app13063434

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