An editorial in December cries out for an end-of-the-year review. Or an outlook for the year ahead.

An editorial in December cries out for an end-of-the-year review. Or an outlook for the year ahead. For me personally, a very special year is drawing to a close. On December 1, I celebrate my first anniversary of joining Kunststoffe. A turbulent year lies behind us. I have traveled far less than I personally would have liked – in keeping with the regulations in force at the time.

Nevertheless, it was a great year for me! I was able to explore new topics for myself, make new contacts and completely immerse myself in the world of plastics. All with the support of a wonderful editorial team. In summer and fall, it was a huge pleasure at last to make on-site visits to customers or attend face-to-face events again.

But now, at this moment, as I write these lines, it looks as though we will still have to remain patient. Though, quite honestly, I’m happy that, for us in the Kunststoffe editorial team, up-to-date articles about infection statistics or regulations are not our issue. We can forget about medical and political statements and keep to the hard facts in the fields of injection molding, extrusion or materials. In this edition, you can find articles about the digital twins for injection molds, trends in materials handling or CO2 reductions through the use of recycled materials or bioplastics.

Analogous to the Covid rule of three – vaccinated, tested or recovered – in the editorial team we have developed our own rule of three for authoring our articles. We want our texts to be substantial, intelligent and credible.

Susanne Schröder [<a href="mailto:Susanne.Schroeder@hanser.de">Susanne.Schroeder@hanser.de</a>]

Editorial Susanne

Schröder, Susanne

On the Way to the Smart Injection Molding Factory

Part 2 of the Series: Integrated Data Acquisition for the Injection Molding Production

Everyone is talking about digitalization and Industry 4.0. In practice, however, implementation is often difficult. The data-driven operation of an injection molding production is often still a dream. Only if the exact actual condition of the machines and peripheral equipment is known, work on optimizing the processes can be done. The Eastern Switzerland University of Applied Sciences describes the challenges that have to be overcome and shows possible solutions based on a self-operated manufacturing cell.

There are two main challenges in implementing Industry 4.0 today [1].

On the one hand, there is often a lack of awareness in practice, both for possible applications and for the necessity of a concrete step-by-step implementation. We are talking about the actual target orientation or also use case definition for the smart factory. This concretization must be oriented to the following questions:

<ul><li>How can I increase my value creation by using data?</li><li>How can I use my data? What is the goal?</li><li>What data do I need to implement a specific use case?</li></ul>

The awareness for possible applications can be created by the use case framework presented in <a ext="tango:{f7174548-8ad9-4017-b06b-55b8e552a559}">the last article of this series (Kunststoffe international 7/21)</a>. This framework was systematized and developed on the basis of realized use cases in practice [2].

On the other hand, learning from data requires a complete database. Some questions arise here as well:

<ul><li>Which signals do I need? Which signals are available at all?</li><li>What quality of data do I need? Is the data available in this required quality?</li><li>How do I get the data out of my machine?</li><li>How do I synchronize data from different machines and devices?</li></ul>

The database is often a major hurdle, as the data is simply not available or not in sufficient quality. In the field of plastics processing, for example, there are no suitable, industry-wide standardized specifications and protocols that can be integrated with a variety of different data sources and database systems without any problems. This lack of standardization has resulted in each machine providing data differently today. Fortunately, many standards and specifications are currently in development (e. g. OPC UA), so interoperability will improve in the future.

Investigations showed that a step-by-step approach to implementing Industry 4.0 in plastics processing is target-oriented. We start with the definition of the use case. Based on this, an initial model for prediction can be developed with a focus on this use case. The validated model can then be integrated into the IT landscape, which is then rolled out in the factory or the entire production network. This is also reflected in the developed model for the implementation of Industry 4.0 in the factory (Fig. 1).

Many expert organizations are currently also dealing with this topic and specifically with the standardization of data. For example, there are also recommendations from the VDI group on which signals should be recorded in the field of injection molding [3].

Newer machines offer increasingly better data availability, i. e. they also enable more and more high-frequency recording of the individual signals and their storage as time series curves. This enables in-depth process analyses, which are essential depending on the use case. For the cyclic export of process parameters, the Euromap 63 and Euromap 77 (OPC UA) interfaces also play an important role here.

At the Institute of Materials Technology and Plastics Processing (IWK), it was possible to set up a data acquisition system to which five different injection molding machines from various manufacturers and various peripheral devices have now been integrated. The recorded data can be visualized and evaluated directly.

A number of challenges had to be overcome in order to set up this type of data acquisition for machine learning. It became clear that device-specific solutions often had to be implemented so that the data could be exported and recorded in the desired quality. This is a hurdle for smaller manufacturing companies in particular, as such interdisciplinary know-how is often not available.

Another difficulty is the synchronization of data from different machines and devices (e. g. injection molding machine, temperature control units, ambient conditions). Each device usually works with its own time stamp. This is a common problem, especially when working with time series of different devices. This can be avoided by setting up a live system in which all data is recorded synchronously. The time stamp is assigned by the data acquisition system. However, this requires that all machines and devices provide the data live. This means that curve data, which for example is made available via the OPC UA interface at the end of the cycle as time series histories, is not suitable for this purpose. A direct query of strongly time dependent signals (e. g. injection pressure or screw position) via OPC UA in high frequency is not suitable due to the limited publishing interval of the interface (usually max. 200 to 500 ms). However, it is possible to query pre-calculated parameters (such as maximum or average values) at the end of each cycle, and these data can also be combined with curve data. Nevertheless, aggregation already results in a loss of information. Depending on what is to be learned from the data, this can of course be critical. Older machines, which do not support such interfaces and do not store raw data at all due to limited storage capacities, present an additional difficulty.

In addition to synchronization, the allocation of data from different pre or post-processes is also an issue. On the one hand, data acquisition differs between continuous processes, e. g. material drying, in which continuous time series are recorded, and discontinuous processes such as injection molding and, for example, welding as a follow-up process, in which the data are recorded for each cycle and at a defined sampling rate. On the other hand, the data from the pre-process steps must then also be able to be clearly assigned to the later data of the part. For injection molding, this means which material batch was processed and how long was the material used, to manufacture the molded part, pre-dried? This is not a simple question, which is why it is currently still being worked on. For follow-up processes, this is much easier, since the part and the associated data already exist and only need to be expanded.

Fully Automated and Self-Learning Manufacturing Cell

One implementation of this connected factory is a manufacturing cell for the production of a floorball (Title figure and Fig. 2). The ball halves are manufactured on an injection molding machine, laser marked, completely measured in three dimensions and then stored in an interim storage system sorted by color. A collaborative robot is used for automated handling.

For customer orders, this robot takes the ball halves in the desired color from the storage system and transfers them to the welding machine, where the halves are welded into a ball fully automatically. This is a fully connected and automated production cell, the process data of all production steps as well as the quality characteristics are stored in the cloud and can be clearly assigned to each ball. On the one hand, this ensures complete traceability and, on the other, the entire production process can be optimized by using artificial intelligence and advancing towards zero-defect production. This manufacturing cell serves as a training object for students of the OST –Eastern Switzerland University of Applied Sciences and shows companies the possibilities of digitalization.

Use of Data Acquisition for  Research Projects

The data acquisition system also serves as the basis for the use of artificial intelligence in a wide range of projects in the field of injection molding. A central topic is the early detection of process anomalies on the basis of process data. When an anomaly occurs, the machine operator should also be given a recommendation for a suitable countermeasure. This topic is being investigated in a three-year publicly funded research project with five industrial partners.

The process anomalies can be reliably detected and first appropriate countermeasures can be suggested. With the use of a support vector machine and an autoencoder an anomaly score (Fig. 3, top left) can be calculated based on various features. This indicates how stable the current process is running. When this score increases, a recommendation for action is suggested to the operator (Fig. 3, bottom right), which can be used to correct the process.

Other use cases include the prediction of the quality characteristics of the manufactured parts on the basis of process data and predictive maintenance or detection of wear on tool or machine components.

[1] Hopmann, C. & Schmitz, M. (2021). Plastics industry 4.0: Potentials and applications in plastics technology. Hanser Publishers; Hanser Publications.

[2] Budde, Lukas, Hänggi, Roman and Friedli, Thomas. „Digitalisierung à la carte: Individuelle Auswahl von Use Cases nach strategischen Prioritäten“ Zeitschrift für wirtschaftlichen Fabrikbetrieb, vol. 113, no. 12, 2018, pp. 850–854. <a href="https://doi.org/10.3139/104.112016" target="_blank">https://doi.org/10.3139/104.112016</a>

[3] VDI-Gesellschaft Materials Engineering (2019). VDI-Statusreport Industrie 4.0 in Spritzgiessunternehmen.

Fully automated manufacturing cell for the production of a floorball at IWK’s technical laboratory in Rapperswil, Switzerland

16:9

Fig. 1. Model for the implementation of machine learning in the factory

Source: © OST – Eastern Switzerland University of Applied Sciences; graphic: © Hanser

Fig. 2. Production flow of fully automated manufacturing cell

Fig. 3. GUI (Graphical User Interface) for anomaly detection and countermeasure proposal 

Ostschweizer FH - Hauptartikel

Curdin Wick, M.Sc., is head of the injection molding department at the Institute of Materials Technology and Plastics Processing (IWK) at Eastern Switzerland University of Applied Sciences (OST).

Prof. Dr.-Ing. Frank Ehrig heads the Institute for Materials Technology and Plastics Processing (IWK) at OST.

Prof. Daniel Schwendemann is head of the compounding and extrusion department at the Institute of Materials Engineering and Plastics Processing (IWK) at OST.

Prof. Dr. Roman Hänggi is a partner at the Institute for Product Design, Development and Construction (IPEK) and Professor for Production Management at OST.

Adrian Rüedy, M.Sc., is project manager at the Institute for Product Design, Development and Construction (IPEK) at OST.

The last article in this series takes a look at the challenges involved in implementing specific use cases and learning from data with the help of artificial intelligence in the field of compounding production technology.

Spritzgießen

Kunststoffverarbeitung: Verfahren

Industrie 4.0 für die Kunststoffverarbeitung

Industrie 4.0

Additive Combination Improves Properties and Processability of Biodegradable Polymers

The right additive can enhance the processing and material properties of biodegradable polyesters. Blending a pair of additives into polyesters leads to much stronger effects.

Biodegradable polyesters are difficult to process. However, the right additive can enhance their processing and material properties. Even better results are likely to be obtained by a combination of two such additives: blending a pair of them into polyesters leads to much stronger effects.

The ever-growing problem of plastic waste is boosting interest in biodegradable polymers. After all, biodegradation as an end-of-life option can make a meaningful contribution to a circular economy for plastics [1, 2]. European Bioplastics, an industry association, expects global production capacity for such polymers, and especially biodegradable polyesters, to expand markedly over the next several years [3]. Unfortunately, biodegradable polyesters are still limited in their potential applications. The reason is often a failure to deliver the property profile that compounders, plastics converters and end users have come to expect from conventional thermoplastics. In addition, they are difficult to process. The task of compounding is to offset both these weaknesses.

Polymeric organic additives based on polyvinyl acetate have a proven track record when it comes to modifying biodegradable polyesters. The company Wacker, for example, supplies these under the Vinnex brand, with polarities tuned precisely to biodegradable polyesters. The resulting compatibility makes them highly effective [4]. Also well-known within the plastics industry is Genioplast Pellet, a universal range of silicone-based additives for thermoplastics compounding that is also supplied by the chemical group [5]. These act as processing aids by reducing friction and thereby enhancing the polymer’s end properties.

Tests on PLA and PBS  Biodegradable Polyesters

Applications engineers from Wacker set out to study how a combination of both additive systems might affect the processing and material properties of biodegradable polyesters. The study focused on polylactic acid (PLA) and chalk-filled polybutylene succinate (PBS) which made it possible to look into the additives’ effects on filled and unfilled polymer systems.

Two commercial standard grades of the two polyesters served as polymer matrixes, namely Ingeo Biopolymer 4043 D (PLA) from Nature Works and BioPBS FZ 91 PM (PBS) from PTT MCC Biochem. Both are semi-crystalline, made from renewable raw materials and have been optimized by the manufacturers for the production of plastic film. PLA is known to be a rigid, high-tensile material which is extremely brittle and fragile and has poor thermal stability [6–8]. Its high melt viscosity and low melt strength make melt processing difficult. It also suffers from a low rate of crystallization [9], with post-crystallization being the reason that PLA articles typically become progressively more brittle.

By contrast, PBS has mechanical properties akin to those of polyolefins [10]. Unlike PLA, it is a flexible, tough material of high tensile strength. By virtue of its comparatively high degree of crystallinity [10], PBS has high heat resistance [11, 12]. However, it also has a tendency to post-crystallize on account of its low rate of crystallization [10, 13, 14].

The study was conducted on the additives Vinnex 2504, Vinnex 2525, Genioplast Pellet S and Genioplast Pellet P Plus. Vinnex 2504, a vinyl acetate-ethylene copolymer, was chosen to represent the powder grades from the Vinnex range. It is primarily used by compounders to incorporate soft segments into a polymer matrix. Vinnex 2525, a resin available in pellet form, is a polyvinyl acetate homopolymer. When used as a processing aid, it improves flowability, increases the melt strength and reduces post-crystallization by semi-crystalline polyesters. Genioplast Pellet P plus is approved for food contact. Genioplast Pellet S is primarily aimed at technical applications. There are no significant differences in the properties of these two grades. Therefore, no further distinction will be made between them in the following.

The biopolyesters used in the screening were compounded on a Berstorff ZE-25 twin-screw extruder from KraussMaffei. The compounds were then pelletized and processed into test specimens – injection-molded test panels, flow spirals, blown film and compression molded panels – which were tested and assessed in accordance with industry standards. The non-additive biodegradable polyesters served as references. They were processed in the same way as the others. The modified compounds were produced by incorporating either a Vinnex grade on its own or a combination of a Vinnex grade and Genioplast Pellet into the polyesters. The PLA-based compounds were always unfilled, whereas the PBS-based counterparts contained 15 % chalk.

Silicone Additives Lower Electricity Costs in Processing

In the compounding of filled PBS, addition of friction-lowering silicone pellets reduces the torque demand on the extruder during production of the compounds and leads to lower power consumption. The observed effects may be small, but they can yield appreciable cost savings in large lines.

The flow behavior of the melted compounds was tested using the melt volume-flow rate specified in ISO 1133 and a spiral flow test. In the latter test, the combination of the additive systems makes for a longer flow path. The additive combination generally leads to a substantial increase in the melt volume-flow rate, with combinations with Vinnex 2504 proving especially beneficial to the melt flow (Fig. 1).

Superior Surface Finish for Biodegradable Polyesters

When used in tandem with Vinnex, the chief role of Genioplast Pellet is to influence the material properties. It exerts a particularly great influence on the surface finish of the plastics. The surface roughness of the polyesters is not enhanced by Vinnex on its own, for example. Genioplast needs to be added to lessen the effects of friction. As a result, a coefficient of sliding friction of less than 0.3 can be achieved in the case of both PLA and chalk-filled PBS – this level is required by plastics converters for many applications. In the case of PLA, this level is achieved with a combination of Vinnex 2504 and Genioplast Pellet. In the case of filled PBS, it can be achieved with a blend of Vinnex 2525 and Genioplast.

The reduced surface friction imbues the biopolyesters with greater scratch and abrasion resistance. This is confirmed by visual assessment of abrasion resistance in the Crockmeter test and gravimetric determination of abrasion by the abrasive disk method according to DIN 53754. The friction-reducing effect is especially clear from a confocal microscopic examination of scratch marks produced on smooth injection-molded test panels using a scratch hardness tester (model: 530 P-I; manufacturer: Erichsen): with Genioplast Pellet, the scratches are shallower, the scratch profile becomes flatter and the surface inside the scratch is less rough. This effect is very pronounced at an additive application rate of 2 % (Fig. 2).

Improvements in Longitudinal or Transverse Direction

With regard to the mechanical properties, the study revealed a mixed picture. Combinations of the two additive types yielded improvements in a number of cases but not in others. The effects depend on the grade of Vinnex employed and vary with the polyester matrix. For example, the combination of the two additives produces a higher elongation at break in the case of chalk-filled PBS, but leaves unfilled PLA virtually unchanged.

As expected, Vinnex 2504 acts as an impact modifier for PLA, whereas Vinnex 2525 does not. A combination of Vinnex 2504 and Genioplast Pellet increases the tear strength of PLA blown film in both longitudinal and transverse directions. Combination with Vinnex 2525, on the other hand, leads to a marked improvement in the transverse direction (Fig. 3). The tear strength of the films was determined in the Graves angle test (DIN 53515). The mechanical properties improve, without any impairment of heat resistance. This was confirmed by a determination of the Vicat softening points (Fig. 4) as per ISO 306 (methods A and B).

The studies show that Vinnex and Genioplast Pellet are complementary in their effects and exert a greater influence when employed in combination rather than separately. Both the processing properties and the material properties of the biodegradable polyesters benefit substantially from the additive combination. Such a combination proves especially advantageous in the production of blown film. Here, Vinnex enhances the flowability and melt strength, while Genioplast Pellet increases the take-off and winding speed by lowering surface friction.

In general, the role played by Vinnex in the additive combination is chiefly to influence the behavior of the polymer melt and thus the processing properties, with the choice of grade in many cases exerting a major influence on the resultant effect. When used alongside Vinnex, Genioplast Pellet mainly modifies the material properties. It enhances the surface properties of biodegradable polyesters, without coating the surface in a liquid lubricant film. In general, this additive has a more pronounced effect on filled than on unfilled polymer systems.

Combining both additive systems can help unlock further applications for biodegradable polyesters. The combination greatly mitigates those processing and performance disadvantages – relative to conventional thermoplastics – which have limited the use of these polymers to date. In the usual application quantities and, depending on the system in question, the two additives do not lead to any impairment of degradability, for example, of PBS, PLA or thermoplastic starch and combinations of these biodegradable polymers.

[1] Bauchmüller, V.; Carus, M.; Chinthapalli, R.; Dammer, L.; Hark, N.; Partanen, A.; Ruiz, P.; Lajewski, S.: BioSinn. Steckbriefe sinnvoll biologisch abbaubarer Produkte auf Basis von nachwachsenden Rohstoffen. Abschlussbericht des nova-Instituts für politische und ökologische Innovation, Hürth 2021. <a href="https://renewable-carbon.eu/publications/product/biosinn-steckbriefe-sinnvoll-biologisch-abbaubarer-produkte-auf-basis-von-nachwachsenden-rohstoffen/" target="_blank">https://renewable-carbon.eu/publications/product/biosinn-steckbriefe-sinnvoll-biologisch-abbaubarer-produkte-auf-basis-von-nachwachsenden-rohstoffen/</a>

[2] Biodegradable plastics and the circular economy in Europe. Discussion paper of European Bioplastics e. V.. European Bioplastics, Berlin 2018. <a href="https://docs.european-bioplastics.org/publications/Discussion_paper_Biodegradable_plastics_to_the_Circular_Economy_in_Europe.pdf" target="_blank">https://docs.european-bioplastics.org/publications/Discussion_paper_Biodegradable_plastics_to_the_Circular_Economy_in_Europe.pdf</a>

[3] Bioplastics market data. European Bioplastics, Berlin 2021. <a href="https://www.european-bioplastics.org/market/" target="_blank">https://www.european-bioplastics.org/market/</a>

[4] Weber, K.: The blend makes the difference. Selectively optimizing the material properties of bioplastics. Bioplastics Magazine 9 (2014) 3, pp. 14–16

[5] Geck, M.; Pohmer, K.: Effizient und vielseitig. Pelletierte Siliconadditive für Thermoplaste. Kunststoffe (2014) 9, pp. 178–182

[6] Auras, R.; Harte, B.; Selke, S.: An Overview of Polylactides as Packaging Materials. Macromolecular Bioscience 4 (2004) 9, pp. 853–864

[7] Lim, L.-T.; Auras, R.; Rubino, M.: Processing technologies for poly(lactic acid). Progress in Polymer Science 33 (2008) 8, pp. 820–852

[8] Shen, L.; Haufe, J.; Patel, M. K.: Product overview and market projection of emerging bio-based plastics (PRO BIP 2009). Final report, Utrecht University, Utrecht 2009

[9] Narmon, A. S.; Dewaele, A.; Bruyninckx, K.; Sels, B. F.; Van Puyvelde, P.; Dusselier, M.: Boosting PLA melt strength by controlling the chiralality of co-Monomer incorporation. Chemical Science (2021) 12, p 5672–5681. <a href="https://doi.org/10.1039/D1SC00040C" target="_blank">https://doi.org/10.1039/D1SC00040C</a>

[10] Xu, J.; Guo, B.-H.: Microbial succinic acid, its polymer poly(butylene succinate), and applications. In: Chen, G.-Q. (pub.): Plastics from Bacteria: Natural Functions and Applications. Microbiology Monographs, Vol. 14. Springer-Verlag Berlin und Heidelberg 2010, pp. 347–388

[11] Shen, S.; Kopizky, R.; Tolga, S.; Kabasci, S.: Polylactide (PLA) and its blends with poly(butylene succinate): a brief review. Polymers 11 (2019) 7, 1193. <a href="https://doi.org/10.3390/polym11071193" target="_blank">https://doi.org/10.3390/polym11071193</a>

[12] Zhang, K.; Mohanty, A. K.; Misra, M.: Fully biodegradable and biorenewable ternary blends from polylacdide, poly(3-hydroxybutyrate-co-hydroxyvaleriate) and poly(butylene succinate) with balanced properties. Applied Materials & Interfaces 4 (2012) 6, p 3091–3101. <a href="https://doi.org/10.1021/am3004522" target="_blank">https://doi.org/10.1021/am3004522</a>

[13] Zhan, J.; Chen, Y.; Tang, G.; Pan, H.; Zhang, Q.; Song, L.; Hu, Y.: Crystallization and melting properties of poly(butylene succinate) composites with titanium dioxide nanotubes or hydroxyapatite nanorods. Journal of Applied Polymer Science 131, 11 (2014), 40335. <a href="https://doi.org/10.1002/app.40335" target="_blank">https://doi.org/10.1002/app.40335</a>

[14] de Matos Costa, A. R.; Crocitti, A.; de Carvalho, L. H.; Carroccio, S. C.; Cerruti, P.; Santagata, G.: Properties of biodegradable films based on poly(butylene succinate) (PBS) and poly(butylene adipate-co-terephthalate) (PBAT) blends. Polymers 12 (2020) 10, 2317. <a href="https://doi.org/10.3390/polym12102317" target="_blank">https://doi.org/10.3390/polym12102317</a>

The additive Vinnex 2525 increases the melt strength of PLA, helping to produce a robust blown film extrusion process and constant film thickness 

Fig. 1. The combination of Vinnex and Genioplast Pellet increases the melt volume-flow rate of filled PBS in particular

Fig. 2. Examination of scratches in test panels of chalk-filled PBS (scratch depth Δz in the chart; scratch profiles in the photos): in the compound containing added Vinnex and Genioplast (right), the scratch turns out to be much shallower and less rough than in the compound containing no added Vinnex 2525 (left) and the compound containing added Vinnex 2525 only (center) 

Fig. 3. The combination of Vinnex 2504 and Genioplast Pellet increases the tear strength of PLA blown film in both the longitudinal and transverse directions. The combination of Vinnex 2525 and Genioplast Pellet only increases the transverse direction of the film

Fig. 4. The additive combinations lower the softening temperature of chalk-filled PBS only marginally

KU 11-21_Wacker - Hauptartikel

Dr. Lada Bemert is Head of Business Incubator and Senior Business Development Manager at Wacker Chemie AG. She is responsible within the Polymers business division for global business development of the Vinnex and Nexiva product groups; <a href="mailto:lada.bemert@wacker.com">lada.bemert@wacker.com</a>

Oliver Fuhrmann is Senior Technical Manager Plastics for the Genioplast Performance Additives product line within Wacker Silicones; <a href="mailto:oliver.fuhrmann@wacker.com">oliver.fuhrmann@wacker.com</a>

Karl Weber is Senior Technical Manager at Wacker Polymers; <a href="mailto:karl.weber@wacker.com">karl.weber@wacker.com</a>

Biokunststoffe

Kunststoff Werkstoffe

Kunststoffe, bioabbaubar

Additive

Bioplastics with Coffee Grounds as a Bio-Based Filler

After oil extraction and drying, Coffee grounds can be incorporated into plastic compounds as a filler and coloring agent.

Coffee grounds are much more than just a waste product. After oil extraction and drying, it can be incorporated into plastic compounds as a filler and coloring agent. It also affects the crystallization behavior and influences the continuative plastics processing. In injection molding, this allows cooling and cycle times to be reduced without significantly affecting the material performance.

Bioplastics are mainly used as a sustainable alternative to conventional plastics. However, the additives often come from fossil sources, which contradicts sustainability requirements. That is why intensive research is being carried out on bio-based additives. One possibility is coffee grounds, for example, which can be used both as a filler and as a coloring agent for bioplastics. The material fulfills the sustainability requirement in two ways: it is bio-based and, as a waste product, it also complies with the cycle concept.

How the material can be used as a filler was examined at the IfBB – Institute for Bioplastics and Biocomposites at the University of Applied Sciences and Arts in Hanover, Germany. The biopolymer used was a stereo complex polylactide (PLA; type: IfBB-Blend HD130x) from the University of Applied Sciences and Arts in Hanover based on PLLA (poly-L-lactide) and PDLA (poly-D-lactide) as well as talc as a mineral filler. This material is already used in the office area and was further modified with coffee grounds for the examinations. Additivating PLLA with PDLA as a nucleating agent and combining it with an increased mold temperature of 100 °C results in what are known as so-called stereo complexes (scPLA) in the injection molding process, which in turn determine the crystallization behavior of the material and favor the material properties, in particular the heat deflection temperature. [1]

Different Concentrations  of Coffee Grounds

In order to analyze the influence of the coffee grounds, these were first added in various concentrations of 5 to 15 wt. %. In addition, a compound with 5 wt. % of coffee grounds and 5 wt. % of talc was produced. This was done to check whether the mineral filler is still necessary as a nucleating agent. The coffee grounds used (particle size: d50-value = 362 µm) were obtained from the company abc – advanced biomass concepts GmbH, Cologne, Germany.

The coffee grounds compounds were produced on an extruder ZE 34 Basic from KraussMaffei Extrusion GmbH. The biopolymer matrix is fed into the melting zone at the beginning of the extruder. The coffee grounds (5.4 wt. % moisture) are metered using a side feeder. Adapted screw configurations allow gentle incorporation without damaging the PLLA and the residual material. A special extruder setup with degassing zones allows moisture to be removed from the process, eliminating the need for pre-drying.

An injection molding machine KM 50–180 AX from KraussMaffei with a mold temperature of 100 °C was used to produce the multi-purpose test specimens (type 1A). In order to prevent material degradation due to hydrolysis, the granulates were dried before processing (moisture content &lt; 500 ppm) [2]. Temperature zones, holding pressure as well as injection time and injection pressure were specifically adapted in order to produce an optimally filled component. Following processing, the mechanical, thermal and rheological material properties were determined according on the relevant standards. The fact that the coffee grounds compounds produced can be used for example for catering supplies, computer accessories and the office area is exemplified by two products made from them at the IfBB: a bottle opener and the housing of a computer mouse (Title figure).

Shorter Cycle Times by Combining Coffee Grounds and Talc

The coffee grounds compounds were extruded without any process problems with a throughput of 50 kg/h. In the case of injection molding, it was found that the cycle times increase by up to 28 s with increasing coffee grounds content (5 – 15 wt. %) (Table 1). The cooling time had to be extended in order to avoid imprints of the ejectors due to the poor form stability. The addition of the mineral filler has a positive effect on the compound’s ability to crystallize. The cycle time can be reduced by a further 9 s compared to the reference.

With increasing coffee grounds content, there is a reduction in tensile strength, tensile modulus of elasticity and impact strength. As with the addition of natural fibers or wood flour, the tensile strength and impact strength decrease depending on the dosing quantity [2]. Compared to the reference (scPLA + 10 wt. % talc), the coffee grounds have no reinforcing effect up to a filler content of 15 wt. %. Thus, there is no significant difference in the mechanical properties as a function of the dosing quantity. The heat resistance is above 100 °C for all materials.

The use of talc in the coffee grounds compound increases the tensile modulus of elasticity compared to the compound with 5 wt. % of coffee grounds. This makes the material stiffer, but not more brittle. Addition of talc has no significant influence on tensile strength and impact strength [3].

Differential thermal analyses (DSC tests) were carried out in order to analyze the crystallization behavior more precisely, especially with regard to insufficient demolding during injection molding due to the low form stability of some compounds. The DSC cooling curves show that as the proportion of coffee grounds increases, there is a broadening and shifting of the crystallization peak towards lower temperatures (Fig. 1). The end of the crystallization of the samples with 10 or rather 15 wt . % of coffee grounds was below the set mold temperature of 100 °C. This suggests that crystallization has not been completed during the injection molding process. Since the crystallization peak shifts towards lower temperatures at higher cooling rates, long cycle times arise. [4]

In order to be able to assess the crystallization behavior more precisely, images were taken under polarized light using a hot stage microscope. The sample was heated above the melting point (175 °C for PLLA; 245 °C for scPLA) and cooled down in a defined manner (10 K/min). The beginning and formation of the crystals during cooling were recorded and evaluated microscopically.

The crystallization behavior of the sample added with coffee and talc (scPLA + 5 wt. % talc + 5 wt. % coffee grounds) is shown in Figure 2. The polymer portion is completely melted at 245 °C. The pink areas show the liquid, crystal-free state of the compound. The homogeneously distributed coffee particles and the glowing crystalline structures of the talk can be seen. During the cooling process, the first crystals arise in the edge area of the sample at 130 °C. Small spherulites form with decreasing temperature, similar to injection molded components, from the outside to the inside and on the coffee particles. The crystallization is already fully completed between 109 and 110 °C and is therefore 9 °C above the set mold temperature. This result coincides with the result obtained from the DSC cooling curve (Fig. 1). The addition of talc leads to an increase in the crystallization temperature (Tc) and thus to nucleation and a shortening of the crystallization period of the coffee grounds compound.

Based on the results, the compounds with 10 and 15 wt. % of coffee grounds were processed and analyzed again at a lower mold temperature of 90 °C. The results show that the cycle time can be reduced by 7 to 12 % by adjusting the mold temperature (Table 2). Due to a lower mold temperature the increased crystal formation leads to sufficient form stability and thus to better demolding. This assumption was confirmed by further DSC measurements at the component. As the degree of crystallization increases, the tensile strength decreases by approx. 13 %, the tensile modulus of elasticity by approx. 3 % and also the impact strength.

The industrial processing of the coffee grounds compounds can be realized without any process problems. By adapting and adjusting the peripheries, time and thus costs can be saved. The material properties change due to the addition of coffee grounds, similar to the use of natural fibers or wood flour. Tensile strength, impact strength and also the flowability decrease with increasing coffee grounds content. Especially the combination of coffee grounds and the mineral filler talc is promising. Both material properties and processing parameters such as cooling and cycle times are improved by shortening the crystallization period.

[1] Siebert-Raths, A. Modifizierung von Polylactid (PLA) für technische Anwendungen: Verfahrenstechnische Optimierung der Verarbeitungs- und Gebrauchseigenschaften. Rostock: s.n., 2012. Dissertation. (Modification of polylactide (PLA) for technical applications: procedural optimization of processing and usage properties. Rostock: s.n., 2012. Dissertation)

[2] Institut für Biokunststoffe und Bioverbundwerkstoffe. Identifizierung und praktische Umsetzung von Synergien im Bereich der Biopolymere, Biopolymerfasern und Verbundwerkstoffe inklusive Optimierung zugehöriger Prozesstechnik und Verarbeitung zur anwendungsorientierten Weiterentwicklung. Hannover: Hochschule Hannover, IfBB – Institut für Biokunststoffe und Bioverbundwerkstoffe, 2018. S. 45–48, 61, 65–69, 78, Schlussbericht. Förderkennzeichen: 22024711, 11NR247. (Identification and practical implementation of synergies in the field of biopolymers, biopolymer fibers and composite materials including optimization of the associated process technology and processing for application-oriented further development. Hanover: University of Hanover, IfBB – Institute for Bioplastics and Biocomposites, 2018. pp. 45–48, 61, 65–69, 78, final report. Funding number: 22024711, 11NR247.)

[3] Jahn, D. und Siebert-Raths, A. IBÖM02: KaVe – Entwicklung eines hochwertigen Bioverbundwerkstoffs auf Basis von Kaffeesatz. Kunststoffverarbeitung, Hochschule Hannover, IfBB – Institut für Biokunststoffe und Bioverbundwerkstoffe. Hannover: s.n., 2020. Schlussbericht. (KaVe – development of a high-quality bio-composite material based on coffee grounds. Plastics processing, University of Hanover, IfBB – Institute for Bioplastics and Biocomposites. Hanover: s.n., 2020. Final report.)

[4] Ehrenstein, Gottfried W. Thermische Analyse – Brandprüfung, Wärme- und Temperaturleitfähigkeit, DSC, DMA, TMA. München: Carl Hanser Verlag, 2020. S. 88–89. 978–3–446–46258–8. (Thermal analysis – fire test, thermal and thermal conductivity, DSC, DMA, TMA. Munich: Carl Hanser Verlag, 2020. pp. 88–89. 978–3–446–46258–8

The coffee grounds compounds can be used for computer accessories such as a housing of a computer mouse

Table 1. Material properties of the coffee grounds compounds (mold temperature during injection molding 100 °C)

Table 2. The mechanical properties of the components produced by injection molding differ using different mold temperatures

Fig. 1. As the proportion of coffee grounds increases, the crystallization peak is broadened and shifted towards lower temperatures

Fig. 2. Hot-stage microscope images for a sample made from scPLA with 5 wt. % of talc and coffee grounds each: the melted state of the sample at 245 °C can be seen on the left. The picture at the middle shows the crystal formation in the edge area at 126 °C. Crystallization is completed at 110 °C (right)

KUint9-21_IfBB_Kroll - Hauptartikel

B. Eng. Daniela Jahn is scientific assistant at the IfBB – Institute for Bioplastics and Biocomposites at the University of Applied Sciences and Arts in Hanover, Germany, where she works in material development and thermal analysis; <a href="mailto:daniela.jahn@hs-hannover.de">daniela.jahn@hs-hannover.de</a>

Dr. Stephen Kroll is senior engineer at IfBB and heads the team sustainability; <a href="mailto:stephen.kroll@hs-hannover.de">stephen.kroll@hs-hannover.de</a>

Prof. Andrea Siebert-Raths is professor for products and processing of renewable raw materials and head of the IfBB; <a href="mailto:andrea.siebert-raths@hs-hannover.de">andrea.siebert-raths@hs-hannover.de</a>

The project “KaVe – Development of a high-quality bio-composite material based on coffee grounds” was funded by the German Federal Ministry of Education and Research (BMBF) (funding code 031B0383C). The authors would like to thank the project partners abc – advanced biomass concepts GmbH and Maschinenfabrik Reinartz GmbH & Co. KG for the promotion and support.

Füllstoffe, mineralisch

Füllstoffe für Kunststoffe

Füllstoffe, allgemein

Integration of Digital Watermarks in Complex Injection Molded Packaging Products

For the first time a readable digital watermark, imperceptible to the naked eye, has been incorporated into an injection-molded flip cap.

Digital watermarks can make the sorting of post-consumer plastic waste more accurate and efficient in the future. For the first time, through advancements in injection molding technology, a readable digital watermark, imperceptible to the naked eye, has been incorporated into an injection-molded flip cap.

Currently, a large proportion of collected post-consumer plastic packaging still cannot be recycled. One of the main reasons for this is that the exact composition of the plastic molding compound cannot be detected during the sorting process. However, higher sorting rates between 95 and 100 % represents one of the essential goals to transition from a “Linear Plastics Economy” to a “Circular Plastics Economy.” Therefore, in 2016, the HolyGrail initiative was initiated to develop solutions for sorting plastic packaging under the leadership of The Procter & Gamble Company and facilitated by the Ellen MacArthur Foundation. The project analyzed different technologies for the detection of plastic packaging. In 2018, the technology of a visually imperceptible digital watermark was finally selected. [1]

The follow-up project, Digital Watermarks Initiative HolyGrail 2.0, driven by AIM – European Brands Association and powered by the Alliance to End Plastic Waste, was officially launched in September 2020. The objective of the initiative is to investigate digital watermarks from insertion to pilot sorting systems for various plastic packaging, enabling industrial scale-up. Foboha (Germany) GmbH, a business within Barnes Molding Solutions, is actively participating as a “technology enabler” in injection molding technology, strongly contributing to the working group to introduce digital watermarks into injection molds and define guidelines.

The Advantage of Digital Watermarks in the Sorting Process

Sorting by grade is the most important criteria in the recycling process for the subsequent recyclate quality. Today, plastic waste can be identified at high speed based on physical properties such as near-infrared sorting. One of the limiting factors is that dark-colored plastics often cannot be identified [2]. Alternatively, localized information can be placed on the product directly in the molding process using identification stamps, such as the ASTM International Resin Identification Coding System introduced in 1988 [3].

In comparison, digital watermarks are almost invisible and offer the possibility of integrating information over the entire surface. These are technical, hidden markings embedded in a carrier medium, such as in the printing of packaging. The digital watermarking technology currently being used in the HolyGrail 2.0 initiative is being developed by Digimarc Corporation. In a simplified description, a limited, pixel-based barcode 22 x 22 mm² in size is applied on the whole product surface like a mosaic.

The digital watermark itself is an overlay of a message signal for addressing a database entry and a synchronization signal to determine the objects’ orientation. By integrating camera-based detection systems into sorting systems, information including plastic type, additives, or application area (such as food/non-food) can be read out from a database.

In terms of the application method, a distinction can be made between print-film-based and mold-based processes (Fig. 1). In the former, the digital watermark is integrated two-dimensionally into the pixels of the print. Films printed in this way have already been studied in various processes. In mold-based processes, a three-dimensional digital watermark is molded onto the surface of the plastic component. Blow molding and thermoforming processes have also been investigated: with these methods, the forming occurs in the rubber-elastic state; thus, the molding accuracy is lower than in injection molding. Therefore, conical or cylindrical spikes are used, where the digital watermark is more coarsely marked and can be more easily perceived by the customer. [4]

Fine holes in the mold surface can be used in injection molding (Fig. 1, right) instead of larger protruding spikes. The molding accuracy of such microstructures between 0.5 and 500 µm is influenced by the processing properties of the plastic and by the process parameters. High holding pressure, short injection times, high mold temperatures, and melt temperatures have a positive effect [5, 6].

In the case of digital watermarks for plastic packaging, the focus is on readability instead of precise molding. The structures must be large and deep so they can be molded reliably and simultaneously have as little impact as possible on the appearance of the plastic part. In the packaging industry, the digital watermark must also be reliably molded without increasing the melt or mold temperature, as an extension of the cycle time will often not be tolerated.

First, preliminary tests are carried out on the readability of variations of the digital watermark with different texture depths on injection-molded test plates (180 x 150 mm²) (Fig. 2). The plate thickness is set at 1.1 mm so that it reflects the wall thickness range of subsequent applications and is gated by a film gate. The mold insert is mirror polished. Using a laser texturing process, seven variations (VDW) of the digital watermark (columns) in the texturing depths TDW 2, 4, 8, 15 and 30 µm (lines) are introduced into the mold insert by the company Reichle Technologiezentrum GmbH. Standard laser texturing with matte structures is used in the area marked in turquoise, while high-gloss laser texturing is used in the red area with a new process developed by Reichle. For example, the VDW 1 used (few, small dots) is shown in Figure 2, left. The black areas are laser textured as a depression in the surface.

Readability of Digital Watermarks on Injection Molded Parts

The test plates are molded with a polypropylene molding compound suitable for caps and closures (grade: Moplen RP340N, manufacturer: LyondellBasell). In addition, the naturally transparent molding compound is colored for the tests with 2 % color masterbatch in blue transparent, black, and white – both latter being opaque. The influence of the variation VDW on the appearance of the surface can be seen on the black test plate shown in Figure 2.

While only a slight effect on the gloss of the plate can be seen purely optically with the dot-shaped codes, the “splash”-like variation of the digital watermark leads to a duller surface. This correlates with the percentage of black areas (depressions). Therefore, these variations are only suitable for matte items and will not be analyzed in more detail below.

In the dot variations, the visibility of the digital watermark becomes more visible as the number and size of the dots increase. In the macro images of the example of VDW 1 (Fig. 3), the textures stand out brightly from the molded surface. When the texture is molded, a small irregular surface structure is created on the plastic part, which leads to light scattering and thus contrast with the highly polished surface.

Using standard laser texturing with a depth of 2 µm, the structure is flat with a diameter of approx. 160 µm. With high-gloss laser texturing, the structure stands out less strongly at the same texture depth and is thus more difficult for the human eye to detect. With a texture depth of 30 µm, the diameter increases to approx. 180 µm, and the structure is formed on the surface as a hemisphere a few micrometers high. Variations 3 and 4, which are not shown, have a larger structure diameter of approximately 240 µm. This increases the surface area by more than 100 %, making the digital watermark more easily visible to the naked eye.

Indirect Readability Only  with Transparency

On the test plates, the readability of the digital watermark is analyzed for each texture field with the support of the Digimarc company using the camera system and evaluation algorithm developed for HolyGrail2.0. Figure 4 shows the evaluation of the readability using four signal bars following the arrangement on the test plate (Fig. 2). Two bars represent the limit above which the digital watermark can be read.

In the direct measurement on the side of the digital watermark, good to excellent readability is given for transparent, blue, and black test plates for all dot structures (VDW 1 to 4) and in all texture depths. Thereby, the trend of readability of variants with many dots is slightly better. The texture diameter and texture depth have no significant influence on the readability.

In the case of white-colored test plates, the digital watermark is only readable with large texture diameters and texture depths. The reason for this is the lack of contrast between the highly polished surface and the molded textures (Fig. 4, top). Despite the lower contrast (Fig. 3), the readability of the high-gloss laser-textured digital watermark is comparable to that of standard laser texturing.

Complementing the direct measurement, indirect readability via the reverse side of the plate is investigated for the transparent plates and the blue transparent plates. The advantage of indirect readability would be that only one surface would have to be marked with the digital watermark to ensure suitable coverage of the part surface. For the transparent plate, the readability is comparable to the direct measurement. Indirect readability is prevented by coloring with the blue transparent color additive.

Analysis of the Transferability to a Complex Part

The use of a digital watermark for a complex injection molded part is analyzed using a single-cavity prototype mold for a flip-cap geometry (base area 68 x 38 mm², max. height 42 mm, wall thickness 1.0 to 1.2 mm) by Procter & Gamble (Fig. 5). Based on the preliminary tests, VDW 1 in 2 µm is selected as a combination of good readability with minimal influence on the article’s appearance.

In the first phase, the digital watermark is first added to the highly polished outer surface of the article (orange), and the readability is analyzed for different viewing directions. Due to the mold design, texturing below the film hinge is not possible. In the second phase, the digital watermark is additionally applied to the inside of the lid using high-gloss laser texturing. It is applied to the inner part of the flip cap using standard laser texturing (red), while rotatable elements such as ejector pins are left out. The injection molding parameters used are based on those of the series production process. However, there are extended non-productive times due to the demolding of the cold sprue system of the prototype mold.

The analysis of the molding of the digital watermark shows comparable results to those of the test plate in Figure 4. Here, under magnification, no change in the textures can be detected due to demolding either. Since the readability of the digital watermark has already been demonstrated in the test plate used, the area on which readable digital watermarks are detected is determined instead. Various orientations and conditions (open, closed, detached lid) of the flip-cap are considered (Fig. 5, right), which can occur during sorting. Depending on the orientation, the projected area differs, which must be set in relation to the readable area. Due to the shape of the flip-cap, the angle at which the areas are viewed also differs.

In the case of the cut-off cap, a flat, slightly curved area of about 19 cm² is examined. For all colors, about 95 to 99 % of the digital watermark is readable on the textured side (top), confirming the results of the preliminary tests. The nearly 90 % readable area for the white cap can perhaps be attributed to the curvature of the lid, which increases the contrast. The transparent and blue transparent, 95 % and 70 %, respectively, are still legible from the reverse side. The indirect legibility of the blue transparent cap can be explained by the highly polished surface on both sides but cannot be confirmed conclusively.

Thanks to the texture applied to the inside of the lid in phase 2, a very high readable area percentage can also be achieved with the opaque molding compounds. It must be noted that the textured area is smaller due to the functional elements. An important finding is that a digital watermark introduced on both sides does not disturb readability with transparent components.

When viewed from above, only the top of the cap (when open) and the shell surface are textured in phase 1 demonstrators. When viewed from below, the top of the cap is visible. Although the textured area is approximately 4 cm² larger when viewed from the top, comparable readable area contents of 45 to 52 % of the projected area are measured. This is most likely explained by the angle towards the camera under which measurements are taken in the setups. This can lead to stronger reflection and thus poorer readability and would also explain the results when viewed from the side and in the closed condition.

Due to the almost full cover texturing, except for the white caps, readability of more than 30 % of the projected area can be achieved for all viewing directions analyzed. The texture on both sides has the greatest effect on the transparent demonstrators. A considerable increase is also possible with the black demonstrators. However, the fact that the increase is smaller can be explained by the fact that many of the additionally textured areas have only limited effects in the perspectives investigated or are viewed at a steep angle. In summary, apart from the white demonstrator, a sufficiently large area is readable in phase 2 to allow sorting based on the digital watermark.

In cooperation with partners from the “HolyGrail2.0” initiative, for the first time, Foboha (Germany) GmbH has introduced a readable digital watermark into an injection-molded packaging product using the example of a flip-cap. In addition to the digital watermark’s design and texture’s depth, it was shown that the color of the subsequent article is also critical for good readability. Transparent articles, for example, can enable readability from the back of the article and thus reduce the area to be textured. White, highly reflective surfaces may make readability more difficult due to lack of contrast. The results will be incorporated into a guideline for the future use of digital watermarks.

The flip caps produced in this subproject will be used for sorting trials on a pilot sorting machine to confirm the successful trials. Furthermore, Foboha plans to introduce the texture into a production mold to investigate its durability over the mold lifetime and collect additional results for an industrial scale-up.

[1] N.N.: HolyGrail: tagging packaging for accurate sorting and high-quality recycling. URL: <a href="https://assets.ctfassets.net/oggad6svuzkv/1Mp2tj3PM4L5FR8O5RnC1X/2d498b0c8f0f55540b3b297bc5bf67d2/Holy_Grail_project_summary.pdf" target="_blank">https://assets.ctfassets.net/oggad6svuzkv/1Mp2tj3PM4L5FR8O5RnC1X/2d498b0c8f0f55540b3b297bc5bf67d2/Holy_Grail_project_summary.pdf</a>

[2] Natalie, R.; Kiesel, R; Aumnate, C.: Understanding plastics recycling: Economic, ecological, and technical aspects of plastic waste handling. Carl Hanser Verlag GmbH Co KG, 2020

[3] N.N.: ASTM D7611: Standard Practice for Coding Plastic Manufactured Articles for Resin Identification. ASTM International, 2020

[4] Hopmann, Ch.; Michaeli, W.: Einführung in die Kunststoffverarbeitung. Carl Hanser Verlag GmbH Co KG, 2017

[5] Tosello, G.: Micro Injection Molding. München. Carl Hanser Verlag, 2018

[6] Orth, M.: Füllvorgang von mikrostrukturierten Spritzgießwerkzeugen und Vorhersage zur Strukturabformung, RWTH Aachen, Dissertation, 2021

On the flip cap, the digital watermark is not visually perceptible, but can be read like a code by specialized high speed camera

Fig. 1. Previously investigated applications of digital watermarks in plastics processing

Fig. 2. Geometry textures of the digital watermark and the test plate for testing the readability