Band 41, Heft 10

Among various nanomaterials used for food packaging, zinc oxide (ZnO) nanoparticles are one of the best choices due to their high antimicrobial property. However, for biodegradable materials like poly(butylene adipate-co-terephthalate) (PBAT), biodegradability can be limited by the antibacterial function. Thus, in the present study, reinforced PBAT films with different weight percentages (1, 3, and 5 wt%) of ZnO nanoparticles were prepared by the casting process to investigate the effects of ZnO on the thermostability, mechanical, and antimicrobial properties of the PBAT film. The results showed that the small amount of ZnO (1 wt%) reduced the decomposition temperature of the PBAT film by nearly 50 °C, and the thermal stability was significantly decreased with the increasing ZnO content. Melt flow index comparison showed that the ZnO nanoparticles accelerated the room temperature degradation rate of PBAT films. In addition, due to the degradation effect of ZnO nanoparticles, the mechanical properties such as the total percentage of elongation (at break), the tensile strength, and yield strength decreased with the addition of ZnO nanoparticles. The antibacterial test showed that PBAT + 1 wt% ZnO films could achieve high antibacterial activity ( R  = 6.8) against Escherichia coli . This study is important for controlling the degradation period of biodegradable materials.

This paper describes work carried out to assess the effect of fibre treatments and coupling agent on the mechanical performance of PLA composites reinforced with 20 wt% fibre. The chemically-treated harakeke and hemp fibres used to produce fibre mats. Maleic anhydride (MA) grafted PLA (MA-g-PLA) was used as a coupling agent. Composites with fibre treated with silane and dicumyl peroxide (DCP) and composites using MA-g-PLA were characterised by swelling testing, scanning electron microscopy (SEM), tensile testing, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). It was found that the interfacial bonding for composites with fibres treated using silane and peroxide and composites coupled with MA-g-PLA noticeably improved supported by lower swelling indices, higher tensile strengths and lower tan δ compared to those composites with fibres treated using alkali only, with the highest tensile strength of about 11% higher obtained from composites treated with MA-g-PLA followed by silane and then peroxide. However, using silane, peroxide and MA-g-PLA as additional composite treatments increased significantly the composite failure strain by up 11, 19 and 30%, respectively for harakeke composites and by 13, 24 and 30%, respectively for hemp composites.

Acrylonitrile-butadiene-styrene test specimens were additively manufactured by fused deposition method to investigate the effects of infill pattern and density on wear rate, coefficient of friction, wear mechanisms, and microscopic wear characterization. The surface morphology of specimens was characterized using a scanning electron microscope. Under constant parameters of applied load, sliding speed, and sliding time, wear tests were carried out at room temperature. The study revealed that a grid pattern of high infill density and a honeycomb pattern of low infill density showed the lowest wear rate and lowest coefficient of friction compared to the rectilinear pattern. Infill pattern and density affected the wear rate behavior of specimens directly. Moreover, adhesion between additively manufactured layers along with surface texture affects the wear behavior and wear rate. Increasing infill density allowed poor cooling of previously built layers. Longer process time results in rough surfaces.

Phenolic resin (PR) was grafted onto the surface of graphene oxide (GO) through π–π conjugation and chemical bonding. After carbonization, organic compounds turned into carbon layers with a thickness of about 10 nm and coated on the surface of GO formed a core–shell structure. Besides, the adiabatic interface formed during organic carbonization can effectively connect the aerogels into a three-dimensional network. The optimum mass ratio of GO was determined to be 10 wt% in the preparation of the precursor aerogel. The adiabatic interfaces (carbon) between GO lamellae could effectively reduce the solid phase heat transfer in aerogels (thermal conductivity is 0.0457 W m −1  K −1 ). At the same time, the existence of GO also ensured better mechanical properties of GO/carbon composite aerogel (compressive strength is 2.43 MPa) compared with the pure carbon aerogel (1.52 MPa), demonstrating the excellent heat-shielding performance and mechanical property of GO/carbon aerogel.

Joining technologies have a crucial role in the product development process, e.g. to achieve local part properties or functional integrations. This often requires multi-material joints, which are challenging for conventional joining processes. Therefore, innovative processes are needed to generate bonds between adhesion-incompatible material combinations, such as joining using pin-like structures in the vibration welding process. Investigations into this novel process have provided initial findings; however, a specific pin design is not possible at this time. For this reason, the influence of the pin-foot width of the two joining partners was analyzed numerically by simulation. The results of the simulation were validated by experimental tests. The investigations show, that the simulation model is suitable for predicting the bond quality as well as the fracture behavior of the multi-material joint based on pin-like structures. The developed correlations between material, pin-like structure, and resulting bond quality allow design criteria for the pin-like structures to be derived. These allow a specific dimensioning of the pin-foot ratio depending on the used material combination. Thus, for example, the fracture behavior of the multi-material connection can be selectively adjusted, as well as the bond strength can be maximally utilized.

Solid expandable tubular technology and swelling elastomer seals find extensive use in the repair of aging reservoirs. To improve productivity and cost-effectiveness, they have also become an integral part of new developments such as slim wells and completions with reduced or no cementing. This work reports the use of numerical simulation to investigate the joint use of expandable tubulars and swell packers in various petroleum drilling applications. Material properties of steel tubular and five different swelling elastomers are obtained through mechanical testing. Simulations are performed to study the sealing pressure at the elastomer-formation boundary. Different parameters are studied, such as elastomer material, expansion or compression ratio, seal length, seal thickness, tubular end condition, and formation type. Higher values of rubber elasticity, tubular expansion (expansion ratio), and elastomer compression result in higher seal contact pressure. Contact pressure is higher when the elastomer is pressing against wellbore formation as compared to steel outer casing (zero friction vs. friction), and when the formation is assumed to be rigid as compared to elastic or elastic-plastic. Results of this investigation can be used both for performance evaluation and design enhancement of coupled solid-expandable-tubular and swellable-packer applications.