Haake minijet 2

Biocomposites of PLA with potato pulp powder were prepared by adding the filler PPP in different percentages to the polymeric matrix constituted by the bio-based PLA (with a concentration of 85 wt%), the plasticizer ATBC (with a concentration of 10 wt%), and CaCO₃ (with a concentration of 5 wt%). For comparison, pure PLA and PLA mixed only with the plasticizer ATBC were also processed in the same way.
Before processing, the PLA and potato pulp powder were dried at a temperature of 60 °C for at least 24 h. The PLA-based matrix and biocomposites were prepared by using a MiniLab II HAAKE Rheomex CTW 5—a co-rotating conical twin-screw extruder. The molten materials were transferred from the mini extruder through a preheated cylinder to a mini injection molder (Thermo Scientific HAAKE MiniJet II), which allows the preparation of dog-bone tensile bar specimens to be used for thermal, mechanical, and rheological characterization. The dimensions of the dog-bone tensile bars were as follows: Width in the larger section—10 mm, width in the narrow section—4.8 mm, thickness—1.35 mm, and length—90 mm. The extruder operating conditions adopted for all the formulations are reported in Table 4.
After preparation, all the samples were stored in a desiccator and analyzed the day after in order to avoid physical ageing effects on the physical properties investigated.

The conventional process of melt compounding was used in this study, followed by injection moulding to fabricate samples for tensile testing. Five, 10 and 15 wt% fly ash samples were rotary mixed with as-received HDPE granules and melt compounded using a HAAKE PolyLab Mixer (Thermo Fisher Scientific Inc., Waltham, MA, USA) at 220 °C for 30 min. Then, well-mixed composite batches were removed from the compounder and cooled at normal environment. We name the batches FA5%/HDPE (contains 5 wt% fly ash), FA10%/HDPE (contains 10 wt% fly ash) and FA15%/HDPE (contains 15 wt% fly ash). All the batches of fly ash mixed HDPE (FA/HDPE) compounds and a pure HDPE sample were injection moulded using HAAKE MiniJet II (Thermo Fisher Scientific Inc., Waltham, MA, USA) at 240 °C for 10 sec, forming dumbbell-shaped samples for tensile testing.

For the tensile testing, ISO 527-2 [35 ] type 5 A specimens were obtained by injection molding with the mini injection machine HAAKE MiniJet II (Thermo Fisher Scientific, Waltham, MA, USA). The injection molding processing conditions of the virgin and recycled PP specimens are shown in Table 2.
The tensile tests were conducted on the machine Shimadzu AGS-X-10kN (Shimadzu Scientific Instruments (SSI), Columbia, MD, USA) following the standard ISO 527-1 [36 ]. These tests were executed at ambient temperature in two steps. First, the specimens were pulled with a tensile rate of 1 mm/min to obtain values for calculating the Young modulus. In the second stage, a tensile rate of 50 mm/min was applied and maintained until the specimens ruptured. The data from this second test was used to determine the yield stress (σ_y) and strain (ε_y), and tensile strength (σ_u) and strain at break (ε_b). It should be noted that the latter is especially relevant for the polymer degradation assessment because of this property’s extraordinary sensitivity to any structural change [37 (link)]. For each PP batch, five specimens were tested.

Test specimens for tensile and tensile impact testing, according to ISO 527-2 [54 ] and ISO 8256 [55 ], were produced by injection molding using a Haake Mini Lab II twin-screw extruder coupled with a Haake Mini Jet II injection molding unit (Thermo Fisher Scientific, Waltham, MA, USA). Extrusion temperature was set according to compounding temperature (T_PP: 220 °C for PP and T_PET: 275 °C for PET-based packaging); screw speed was 100 rpm, and mold temperature for injection was 40 °C (pressure: 350 bar, injection time: 10 s).
Specimens for dynamic shear and extensional rheology were produced by compression molding (Collin P 200 P, Maitenbeth, Germany) at a pressure of 100 bar and in line with extrusion temperatures of 220/275 °C. Discs with a diameter of 25 mm and a thickness of 1.2 mm and squares of 0.8 mm in thickness and a side length of 60 mm were generated using punched aluminum frames sandwiched between steel plates and were separated by Teflon^® sheets.
To demonstrate the possibility of film-to-film recycling, the recyclates were converted into 50 µm-thick films using an Ultra Micro blown-film line (LabTech Engineering, Samut Prakan, Thailand). Extrusion temperature was set to 200 °C; the die temperature was 180 °C; the fan for airflow cooling was set to 1700 rpm, and the pull-off speed of both roller sets was 1.1 m/min.

Tensile and tensile impact strength tests were used for the determination of the mechanical properties. The required test specimens were produced using Haake Mini Lab II (Thermo Fisher, Waltham, MA, USA), a twin screw extruder, in combination with Haake Mini Jet II injection molding equipment from Thermo Fisher Scientific (Waltham, MA, USA). The extrusion was carried out at a temperature of 240 °C and a screw rotation of 100 rpm. For the injection molding process, the mold temperature was set at 90 °C, the pressure was 350 bar with an injection time of 10 s.
The test machine for the tensile test (Zwick 050, ZwickRoell GmbH and Co. KG, Ulm, Germany) was used with a test speed of 10 mm/min and was equipped with a 1 kN load cell and an extensometer. The test specimens for these measurements corresponded to the standard ISO 527-2-5A [52 ].
For the tensile impact strength test the specimens were notched on both sides with a Notch-Vis from Ceast and tested according to ISO 8256/1A [53 ] on an Instron Ceast 9050 (2 J hammer; cross head mass = 15 g, Instron, Darmstadt, Germany).

A lab-scale co-rotating twin-screw extruder (Process 11, Thermo Scientific, Karlsruhe, Germany) and piston injection molding apparatus (Haake MiniJet II, Thermo Scientific, Karlsruhe, Germany) were used for the production of a dumbbell-shaped specimen. The dried granulate was fed through the feed hopper at a constant speed of 4 rpm into the twin-screw extruder, equipped with standard screws with a diameter of 11.0 mm and an L/D ratio of 40.0. The screw assembly includes feed screw elements (1.0 L/D), three mixing zones with kneading elements (⅟₄ L/D), and a discharge element (1 ½ L/D) at the end (Figure 1A). A total granulate sample weight of about 10–15 g was used in order to make three replicates per processing condition. The melted polymer was immediately transferred from the extruder die-end into a heated injection cylinder (Figure 1B), which was mounted on top of a heated dumbbell-shaped mold in which the polymer was ultimately injected (Figure 1C). The injection unit pushes the polymer melt in the mold with a piston, resulting in samples of approximately 1.5 g. Afterward, the polymer samples were manually ejected from the mold and conditioned at 23 °C and 50% RH (relative humidity) for at least three days prior to characterization.

A two-step polymerisation approach was carried out to synthesise the PU matrix, as reported in our previous study [21 (link)], with a hard-segment ratio of 75% HS. The in situ polymerisation approach was used for the preparation of PU/GNP and PU/GO nanocomposites with a weight fraction value, for example, of 0.25 g of GNP/GO, added to 100 g of an exact amount of PU polymer for a ratio of 0.25 wt.%, and so on, since the GNP/GO solution was combined with the chain extender in the second stage. After completing the synthesis process, the PU/GNP and PU/GO solutions were dried in a furnace at 80 °C for three days. The test samples of both PU/GNP and PU/GO nanocomposite materials were performed by an injection-moulding process using a Haake Minijet II (Thermo Scientific, Waltham, MA, USA) with a barrel temperature of 200 °C, mould temperature of 50 °C, injection pressure at 850–1100 bar for 10 s, and holding pressure at 400 bar for 5 s. The synthesis process is shown in Figure 2.