Poly(lactic acid) (PLA) holds significant promise as an option in the field of packaging materials due to its biodegradability and antibacterial properties. Therefore, it is vital for developing packaging materials while improving their heat resistance, and transparency is essential for guaranteeing its application. Using a self-assembled nucleating agent with hydrogen bonding and thermodynamically compatible transparent polymethyl methacrylate (PMMA), this study fabricated PLA micro-crystals with an interface blurred grain. Furthermore, the crystalline structure-property relationship was investigated in different isothermal crystallization conditions; it was possible to achieve higher crystallinity while maintaining the transparency of PLA/10 wt% PMMA/0.3 wt% nucleating agent blends. Compared to other temperatures, the crystallization rate of PLA blends under annealing conditions at 90 °C was higher when induced by three different nucleating agents. Particularly, in the presence of the TC-328 nucleating agent, the system exhibited a crystallinity of 32%, the smallest grain size, and an increased Tg of 61.3 °C, as well as an elevated heat deformation temperature (HDT) from 54.13 °C to 63.2 °C. The smaller nucleating agents with high surface energy enhanced the interaction between the PLA and PMMA, enhancing the PLA/PMMA tensile strength and HDT. These findings may pave the way for designing novel blends for packaging or heat-resistant devices.

In this manuscript, an efficient self-reinforcing technology—solid hot drawing (SHD) technology—was combined with green processing supercritical carbon dioxide (SC-CO₂) foaming technology to promote poly (l-lactic acid) (PLLA) to form an oriented micropore structure. In addition, Polydimethylsiloxane (PDMS), with a high affinity of CO₂ and biological safety, was introduced to enhance the nucleation effect in SC-CO₂ foaming and co-regulate the uniformity of oriented micropores’ structure. The results showed that orientation induced PLLA crystallization, so the tensile strength was improved; the maximum tensile strength of the oriented micropores’ PLLA reached 151.2 MPa. Furthermore, the micropores mainly improved the toughness; the maximum elongation at break reached 148.3%. It is worth mentioning that PDMS can form an antibacterial film on the surface of the material, so that the material has a continuous antibacterial effect.

Hydraulic fracturing technology leads to the development of lots of fractures in the surrounding rock reservoir, forming a three-dimensional fracture network, which plays a role in hindering the transfer of high stress. Under temporal-spatial influence, however, the fracture networks of different media will appear, mainly including water medium fractures and air medium fractures. Clarifying the influence of different medium fractures on the stress transfer is quite important for the layout of the three-dimensional fracture network. In this study, the effects of air and water medium fractures on stress transfer were explored through fracture mechanics theory, and Split Hopkinson Pressure Bar (SHPB) test. Under the joint action of fractures and stresses, the rock mass will form an undamaged zone, a damaged zone around the fracture, a damaged zone under the primary action of stress wave, and the damaged zone under repeated action of reflected stress wave, a model of dynamic load stress transfer hindered by fractures is established, through SHPB test study on dynamic load stress transfer hindered by air/water medium fracture, composite sized fractures, and different impact velocity, the correctness of the model is verified by comparing the theoretical data and experimental data. The results show that air medium fractures can hinder the transfer of stress wave and form a large number of reflected waves to damage the rock mass. The water medium fracture can gather energy, act on the surrounding broken rock mass, form confining pressure, and increase the strength of rock mass, making it difficult to destroy the rock mass under stress action. With the increase of impact energy, the energy absorbed by fractures in water medium is limited, and a large number of stress waves damage rock mass.

Clarifying the mechanical properties and failure patterns of layered coal–rock combinations in coal-measure strata is critical to guiding hydraulic fracturing design in petroleum and mining engineering. This paper investigates the mechanical properties, failure patterns, and stress distributions of sandstone–coal–sandstone (SCS) and mudstone–coal–mudstone (MCM) combinations under different confining pressures and thickness ratios based on the 3D combined finite–discrete element method (3D FDEM). The results show that the mechanical strength of the SCS combination is higher than that of the MCM combination under the same conditions. As the thickness ratio increases, the overall peak stress and elastic modulus of the combination decrease gradually and eventually approach those of the pure coal. As confining pressure increases, the peak stress of layered coal–rock combinations rises gradually, plastic behaviors become increasingly prominent, and the failure mode of the mudstone layer transitions from tensile-dominated to shear-dominated. Under different thickness ratios and confining pressures, the coal layer in the combinations primarily develops shear-dominated cracks, whereas the sandstone layer mainly generates tensile-dominated cracks. An increase in confining pressure elevates the critical thickness ratio for sandstone layer failure in the SCS combination. Essentially, the changes in stress state caused by rock types, thickness ratios, and confining pressures are important reasons for the variations in the failure patterns of each layer in layered coal–rock combinations. The key findings of this paper are expected to provide theoretical guidance for the field design of petroleum and coal mine engineering.

Aimed at the severe strata behavior hazards caused by the occurrence of lateral thick and hard roofs in shallow-buried large-section roadways, a directional fracturing and roof cutting technology for lateral thick and hard roof zones in shallow-buried large-section coal mine roadways is proposed. Key technologies of directional fracturing for such roof regions are investigated using a comprehensive approach including theoretical analysis, numerical simulation, and field testing. The results show that: compared with the minimum principal stress direction, the perforation direction acts as a relatively weak plane and can guide fracture initiation and propagation. Fluid pressure inside arrayed perforations weakens the dominance of the in-situ stress field, promotes fracture connectivity between adjacent perforations, and forms vertical sheet-like fractures around the borehole. Increasing the injection rate and perforation diameter enhances the guidance capacity of arrayed perforations and promotes vertical fracture propagation. As the injection rate increases from 0.12 m³/min to 1.2 m³/min, the fracture height increases by 310.83%; as the perforation diameter increases from 2 cm to 8 cm, the fracture height increases by 31.44%. However, increasing the perforation spacing weakens the influence of fluid pressure inside adjacent perforations, resulting in fracture-free zones between perforations and inhibiting the formation of connected fractures. An arrayed perforation directional fracturing technology for lateral thick and hard roofs in shallow-buried large-section roadways is proposed, with the following parameters: perforation diameter of 8 cm, perforation length of 50 cm, injection rate of 1.2 m³/min, and perforation spacing of 20 cm. Industrial application tests were carried out in the 122105 working face of Caojiatan Coal Mine. Monitoring and evaluation of the perforation-guided fracturing effect were conducted using microseismic monitoring, roadway section scanning, and bolt/cable stress measurement. The results indicate that arrayed perforation-guided fracturing can promote timely caving of the thick and hard roof, effectively reduce strata behavior intensity, and mitigate roadway deformation. This study can provide a reference for the prevention and control of severe strata behavior hazards associated with lateral thick and hard roofs in shallow-buried large-section roadways.