Basalt fibers, similarly to other silicate fibers, can be introduced into both thermoplastic and thermosetting polymer matrices. In this work some basalt fiber reinforced polypropylene composites were investigated. The fiber‐matrix adhesion was improved by commercial and non‐commercial maleic anhydride derivatives. The latter types, called reactive surfactants, were prepared in laboratory scale and the progress of the syntheses was determined by Raman microscopy. The additives allowed performing reactive interface modification during the compounding process. Due to the interface modification with the additives in low concentration the mechanical properties improved. The boundary layers on the surface of the reinforcing fibers were observed using scanning electron microscopy (SEM).
In this article, we investigated the thermoformability of poly(lactic acid) (PLA) films with various D‐Lactide contents and therefore different crystallization properties, performing tensile and ball burst tests at various temperatures and testing rates. We found that the behavior of the PLA films tested above the glass transition temperature significantly differs due to the difference in D‐Lactide content, and thus crystallinity. During tensile testing, elevated temperatures and mechanical stress caused the crystallization temperature to decrease and thus highly induced crystallization. At the same time, as testing speed was increased, the ability of the polymer to crystallize decreased. In ball burst tests, the PLA films crystallized more than during tensile testing. We described the differences found between tensile testing and ball burst testing, which latter better represents the conditions of thermoforming through inducing biaxial deformation.
Abstract. The effect of basalt fibers, produced by the Junkers technology and used as reinforcement in polymer composites, was modeled on the properties of composites, adapting the statistical fiber mat model of Poisson type. The random distribution was approximated by so-called effective spheres that act as defect sites in composites, reducing their strength. The role of fiber heads in strength reduction and the corresponding failure modes were analyzed theoretically using a model and by experiments performed on specimens containing a single fiber head located at different distances from the crack initiation. The applicability of the model was proven both experimentally and by finite element analysis. Based on all these investigations, the effective cross section reduction, and hence the strength reduction (predicted by the model) caused by the presence of fiber heads was proven.
The complex structure of tyres makes them hard to recycle economically; hence, it is crucial to minimize the generation of tyre waste. Nano‐reinforcement, such as graphene, has the potential to increase the abrasion resistance of rubber and thus their lifespan as well. In this research, hybrid styrene‐butadiene rubber‐based (SBR) nanocomposites reinforced with carbon black, silica and various amounts of graphene nanoplatelets are investigated with great emphasis on their combined effects on the mechanical properties of the rubber samples. Sixty‐five phr of precipitated silica can holistically improve the properties of SBR. However, further addition of carbon black and graphene nanoplatelets to silica‐containing samples do not benefit the properties of the samples. Further studies on the compatibilization of silica with carbon‐based reinforcement are necessary. On the other hand, graphene and carbon black constitute an effective hybrid reinforcement system. The tensile strength and elongation at break of SBR are improved by almost 100% with 10 phr of graphene nanoplatelets in combination with 10 phr of carbon black. However, the abrasion resistance of samples was negatively influenced by the addition of graphene nanoplatelets whenever it was added in combination with other fillers. Silica was particularly effective in increasing the abrasion resistance of rubber.
Rubber waste remains a challenge for material science because its covalently cross-linked structure hinders the establishment of the circular economy of rubber. Devulcanisation may provide a solution, as it converts rubber vulcanisates back into their original, uncured state. Devulcanised rubber may be revulcanised or incorporated into virgin rubber, thus waste is utilized and the use of primary resources is reduced at the same time. In this paper, we treated sulphur-cured EPDM (ethylene propylene diene monomer) rubber on a two-roll mill at various temperatures and frictions. We determined the effectiveness of devulcanisation via Horikx’s analysis, which suggested that low devulcanisation temperatures would result in a 50% decrease in cross-link density with minimal polymer degradation. The devulcanisate was recycled via two methods: (a) revulcanisation with extra curing agents, and (b) mixing it with various amounts of the original rubber mixture, preparing rubber samples with 25, 50, 75, and 100 wt% recycled content. Tensile tests revealed that the samples’ elastic properties were severely compromised at 75 and 100 wt% devulcanisate contents. However, tensile strength decreased only by 15% and 20% for revulcanisates containing 25% and 50% recycled rubber, respectively.
The recycling of ethylene propylene diene monomer (EPDM) rubber remains a challenge, as its cross-linked structure cannot be broken down reversibly. Devulcanization may offer a breakthrough; however, a 100% decrease in cross-link density (CLD) with no chain degradation has never been reported. In this research, sulfur-and peroxide-cured EPDM rubbers of known compositions were devulcanized on a two-roll mill and in an internal mixer. The CLD of both rubber samples decreased by around 85%, while the sol content of the peroxidic devulcanizate was considerably higher than that of the sulfuric devulcanizate (23% vs. 3%). Horikx's theory revealed that sulfur-cured samples showed excellent selectivity for cross-link scission, while peroxide-cured samples suffered degradation. Uncured, cured, and devulcanized rubber samples were mixed into high-density polyethylene at various compositions. Large EPDM rubber contents impaired the mechanical properties of the blends, indicating insufficient adhesion between the two phases. Compounds containing originally uncured rubber mixtures had the most beneficial mechanical properties.
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