Fibers made from biopolymers are one solution for conserving both resources and the environment. However, these fibers currently have limited strengths, which limit their use for textile applications. In this paper, a biopolymer stereocomplex poly(-lactide) (scPLA) formation on a technical scale of high-molecular-weight poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA) is presented. This scPLA material is the basis for further research to develop scPLA yarns in melt spinning with technical strengths for technical application. scPLA is compared with standard and commercially available semi-crystalline PLA for the production of fibers in melt spinning (msPLA) with textile strengths. Differential scanning calorimetry (DSC) gives a degree of crystallization of 59.7% for scPLA and 47.0% for msPLA. X-ray diffraction (XRD) confirms the pure stereocomplex crystal structure for scPLA and semi-crystallinity for msPLA. scPLA and msPLA are also compared regarding their processing properties (rheology) in melt spinning. While complex viscosity of scPLA is much lower compared to msPLA, both materials show similar viscoelastic behavior. Thermal gravimetric analysis (TGA) shows the influence of the molecular weight on the thermal stability, whereas essentially the crystallinity influences the biodegradability of the PLA materials.

Poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA), both available on the market, are blended on a technical scale. Using a special process control, the two materials are blended in a twin-screw extruder at a mass throughput rate of 2 kg/h, resulting in a stereocomplex Poly(-lactide) (PLA) blend. Thermal analysis indicates only one melting point at 235 °C. Both the Raman spectra and X-ray powder diffraction patterns show characteristic features for the stereocomplex PLA. With the available amount of this blend PLA fibers with technical strengths can be developed by melt spinning. As such, the application of the biopolymer PLA can be expanded, leading to substitute the conventional plastics for conserving both the resources and the environment.

The objective of this research is the development of a magnetic sheath-core bicomponent fiber. Therefor technical oxide is mixed in polypropylene using compounding. The compound (sheath) and pure polypropylene (core) are further processed in melt spinning into a magnetic bicomponent fiber with textile strength of 26.36 ± 1.62 cN/tex. Bicomponent fiber yarns can be inductively heated above 175°C in less than 10 s. These fibers could be used for thermal bonding of fiber-reinforced plastics, joining techniques of high efficiency due to their possibility to form a material-bonded connection and fiber orientation in nonwovens through a directional magnetic field.Graphical Abstract

The meltblow process was utilized to produce nonwoven fabrics from polylactic acid (PLA) in order to evaluate the potential of this bio-based polyester as an alternative to conventional polyolefins. Therefore, it was opposed against polypropylene (PP) meltblown as benchmark material, which is commonly used as a filter layer, for example in particle-filtering face masks. PLA was found to be processable at more moderate thermal process conditions, while its fiber diameters showed higher sensitivity to process parameter variation. This allowed the controlled deposition of both fine-fiber meltblown webs, but also coarse – spunbond-like – meltblown fiber webs. These showed minor mechanical performance but sufficient haptics and equal air permeability to spunbond PLA. Electret treatment of fine fiber PLA meltblown (1.43 µm average diameter) resulted in a raise of particle filtration performance (in paraffin oil) from 70% to >97%, exceeding the performance of PP meltblown of same grammage and fiber diameter distribution. The effect was also traceable over storage time (90 days), with just a slight reduction of 5% over the first days. These findings highlight PLA’s potential as a high-performance, bio-based alternative for filtration applications. Furthermore, the results contribute to the understanding of bio-polymer processing by comparing the processability, fiber morphology, and resulting performance of PLA and PP under similar process conditions.

Low molecular weight (70 kg/mol) Polyether-ether-ketone (PEEK) is blended in different ratios with two different high molecular weight (105 kg/mol and 130 kg/mol) PEEK materials. Blending is carried out on a technical scale using a double screw extruder at a mass throughput range of 2 – 3.5 kg/h. The influence of the blends on crystallinity and viscoelasticity (complex viscosity and loss factor) is investigated. A reference to PEEK with medium molecular weight (85 kg/mol) is made. This material has ideal viscoelastic properties for melt spinning fibers with technical strengths of more than 60 cN/tex (792 MPa). A higher molecular weight theoretically leads to higher strength. However, processing becomes more difficult as complex viscosity increases and loss factor decreases. With the bimodal PEEK blends presented in this study spinnability can be customized regarding complex viscosity (100 to 1000 Pa∙s) and loss factor (greater than 5). With the available number of bimodal blends, PEEK fibers with higher strength can be developed on a technical scale.