We investigated the effects of two different types of impact modifiers, i.e. core-shell rubber and aliphatic polyester, on the mechanical and thermal properties of polylactide (PLA) filaments for 3D printing. First, PLA/impact modifier blends with various concentrations of impact modifiers were prepared by melt blending in a co-rotating twin screw extruder and test specimens by injection molding. The mechanical and thermal properties of blends were investigated by tensile and bending tests, dynamic mechanical analysis (DMA) and Charpy impact test. It was found that core-shell rubber remarkably improved Charpy impact strength at loadings above 5 wt % (up to 746 %). As shown by DMA, the PLA/10 wt % core-shell rubber blend exhibited better damping performance as compared to neat PLA over the whole examined frequency range, especially at high frequencies, which explained the increase in impact strength. The filament for a fused deposition modeling (FDM), 3D printer was prepared from blend with the highest impact strength (PLA/10 wt % core-shell rubber), whereas PLA and acrylonitrile-butadiene-styrene copolymer (ABS) filaments were used for reference. Test specimens were prepared by using a consumer FDM 3D printer. The mechanical and thermal properties were investigated by tensile and bending tests, DMA, Charpy impact test, and ultra-fast differential scanning calorimetry (Flash DSC). Specimens from PLA blend exhibited 109 % increase in Charpy impact strength as compared to neat PLA. In contrast to injection molded specimens, 3D printed PLA blend exhibited higher tensile E modulus than neat PLA, which was ascribed to improved interlayer adhesion. Moreover, DMA and Flash DSC analysis of 3D printed specimens showed an increase in the glass transition temperature as compared to injection molded specimens. This phenomenon was ascribed to reduction of free volume because of slow cooling in 3D printing process, which is also the reason for increased tensile E modulus of the PLA blend. All tested PLA, PLA blend and ABS filaments were in amorphous state as shown by Flash DSC analysis. Bending test showed an increased toughness of PLA blend in comparison to neat PLA and also higher toughness as compared to ABS. The modified polylactide (PLA/10 wt % core-shell rubber) filament thus combines easy processability of PLA filament and impact toughness of ABS filament.

New developments in additive manufacturing (AM) are enabling the use of 3D printed parts in increasingly demanding applications, such as in mechanical power transmission systems, where excellent build quality and tribological performance are required. The tribological properties of thermoplastic-based AM technologies are well knowninject, whereas the performance of photopolymer-based AM technologies is very rarely explored. This study aims to provide new insight into the tribological performance of 3D printed parts produced using vat photopolymerization (VPP). Photocurable resins based on aliphatic urethane acrylate oligomers were modified with different solid lubricants (polytetrafluoroethylene (PTFE), graphite and molybdenum disulfide (MoS₂)) and 3D printed using Digital Light Processing (DLP). The mechanical and thermal properties were studied using the tensile tests, Charpy impact tests, Shore D, and dynamic mechanical analysis (DMA). The tribological performance was studied using a Pin-on-Disk tribometer. Among the lubricants, PTFE had the highest impact on the coefficient of friction (µ) and the specific wear rate (w_s). The hybrid lubricant system (PTFE/MoS₂) resulted in excellent tribological performance, where the µ was reduced by up to 52% and w_s by up to 92%.

The quality of plastic gears, especially their durability, is becoming increasingly important due to advances in electric mobility. Therefore, new materials are being developed that must have better mechanical properties, high thermal conductivity for heat dissipation, and tribological properties. The composites of expanded graphite (EG) and glass fibre-reinforced polyamide 6 (PA6/GF) were prepared, and the effect of EG particle size (5μm (EG5) and 1000μm (EG1000)) on these properties was investigated. Composites with different contents (2-10wt) of EG in PA6/GF were prepared using a laboratory twin-screw extruder and then injection moulded in the form of rods and discs required for thermal, thermomechanical, and tribological tests. EG acted as a nucleating agent but hindered the crystallization rate at higher concentrations, which was more pronounced when EG5 was added. Dynamic mechanical analysis showed that the storage modulus increased with the addition of both types of EG. However, the addition of EG5 increased the storage modulus more than EG1000. The lowest coefficient of friction was obtained by the addition of 10wt EG5. The wear increased with the addition of both types of EG, only slightly with the addition of EG1000. The thermal conductivity of the composites with EG increased from 0.42W/mK to 1W/mK. The results show that the use of EG with smaller particle size is much more beneficial than with a larger one.

Engineering polymers reinforced with renewable fibres (RF) are an attractive class of materials, due to their excellent mechanical performance and low environmental impact. However, the successful preparation of such composites has proven to be challenging due to the low thermal stability of RF. The aim of the present study was to investigate how different RF behaves under increased processing temperatures and correlate the thermal properties of the fibres to the mechanical properties of composites. For this purpose, hemp, flax and Lyocell fibres were compounded into polypropylene (PP) using a co-rotating twin screw extruder and test specimens were injection moulded at temperatures ranging from 180 °C to 260 °C, with 20 K steps. The decomposition behaviour of fibres was characterised using non-isothermal and isothermal simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The prepared composites were investigated using optical microscopy (OM), colorimetry, tensile test, Charpy impact test, dynamic mechanical analysis (DMA) and melt flow rate (MFR). Composites exhibited a decrease in mechanical performance at processing temperatures above 200 °C, with a steep decrease observed at 240 °C. Lyocell fibres exhibited the best reinforcement effect, especially at elevated processing temperatures, followed by flax and hemp fibres. It was found that the retention of the fibre reinforcement effect at elevated temperatures can be well predicted using isothermal TGA measurements.