Herein, we report self-emulsifying anionic unsaturated polyester emulsions with different chain segments as novel sizing agents. The epoxy modified unsaturated polyester emulsions were synthesized via a self-emulsifying technique with no organic solvents. Emulsions were characterized by dynamic light scattering (DLS), Zeta potential, centrifuge, and cryo-scanning electron microscopy (Cryo-SEM). The results showed that the emulsions obtained were mono-dispersed nanospheres that had adequate colloidal stability. The maximum Zeta potential of the sizing agent is −52.88 mV. In addition, these emulsions were investigated as the sizing agents in order to improve interfacial adhesion between carbon fibers (CFs) and unsaturated polyester resin (UPR). Compared with the CFs sized with the commercial epoxy sizing agent, the interlaminar shear strength (ILSS) of CF/UPR composites from the CFs sized by these emulsion sizing agents with three different chain structures were enhanced by 25%, 29%, and 42%, respectively. The emulsion sizing agent composed of a flexible segment synthesized from adipic acid, neopentyl glycol, and maleic anhydride is most effective and can achieve the highest enhancement of the ILSS of CF/UPR composites.

In this study, desert sand was used as supplementary materials in alkali-activated cements (AAC) with granulated blast furnace slag (GBFS) and fly ash (FA). For the first time, a systematic investigation was conducted on the effects of various treatment methods and contents of desert sand on the strength and microstructure of AAC. This study also analyzed the X-ray diffractometer (XRD), Scanning Electron Microscopy-Energy Dispersive X-ray Microanalysis (SEM-EDX), Mercury Intrusion Porosimetry (MIP), pH values, and Fourier-transform infrared spectroscopy (FT-IR) properties of AAC pastes containing differently treated desert sand to uncover the mechanisms by which these treatments and dosages influence mechanical properties of AAC. Untreated desert sand (DS), temperature-treated desert sand (DS-T), and ground desert sand for two different durations (20 mins and 30 mins) all exhibited some pozzolanic activity but primarily acted as fillers in the AAC pastes. Among the samples, DS-T demonstrated the highest pozzolanic activity, though it was still less than that of fly ash (FA). The optimal dosage for the modified desert sands was determined to be 10%. However, The optimal dosage of different modified desert sands is 10%. The flexural strength of DS-G30-10 reaches 6.62 MPa and the compressive strength reaches 72.3 MPa, showing the best comprehensive mechanical properties.

The study investigated the effects of a toughening agent and micron-sized toughening particles (TP) on the resin and carbon fiber-reinforced polymer (CFRP) composites, with a particular focus on compressive strength. The results showed that the addition of the toughening agent improved the overall mechanical properties of both the resin and CFRP but had a minor effect on the residual compressive strength (CAI) of CFRP after impact. Compared to the pure toughening agent, the addition of TP increased the CAI, GIC, and GIIC of CFRP by 74%, 35%, and 68%, respectively. The SEM, ultrasonic C-scan, and metallographic microscopy were used to analyze the failure morphology and TP distribution. Compared to pure toughening agent modification, the introduction of TP led to the formation of continuous toughening particle layers, which reduced the compression damage area by 61%, significantly balancing and absorbing the load. This modification also resulted in typical kink band damage. This study found that resin toughening significantly improved the compressive strength of CFRP, while micron-sized toughening particles, in the form of toughening layers, notably improved the CAI. These findings provide valuable insights for enhancing the compression and impact resistance of CFRP.

This study primarily investigates the effect of fly ash (FA) content on the mechanical properties and hydration performance of alkali-activated ground granulated blast furnace slag cement (AAGC) and compares the related properties with ordinary Portland cement (OPC). Additionally, we examined the hydration products; performed thermal analysis, MIP, and SEM; and determined chemically bound water and pH values of AAGC. The compressive strength of AAGC showed a retrogression phenomenon from 3 to 28 days, with the 14-day and 28-day compressive strengths of AAGC being higher than those of OPC. The AAGC with 20% FA content exhibited the highest 28-day compressive strength (75 MPa). The hydration heat release rate curve of OPC and AAGC was divided into the initial induction period, induction period, acceleration period, deceleration period, and steady period. As FA content increased, the 28-day pore volume of AAGC increased, while pH values and chemically bound water decreased. SEM images of AAGC with low FA content showed more microcracks.

The poor impact resistance of carbon fiber reinforced composites limits their application in broader fields. In this study, a toughened epoxy resin (E2) modified with toughening agents and a micron-sized toughening particle (TP) were developed. Standard epoxy resin (E1), toughened epoxy resin (E2), and TP-toughened E2 resin (E3) were prepared into prepregs with SYT55-12K carbon fiber and ultimately fabricated into carbon fiber reinforced composites. The mechanical properties of the resins and the composites, particularly the compression properties, were characterized. The failure morphology of the composites and the distribution of toughening particles were observed using scanning electron microscopy (SEM), ultrasonic C-scan testing, and metallographic microscopy. It was found that the toughening agents improved the bending strength of the resin by approximately 12%, while the incorporation of TP enhanced the impact performance of the resin by 122%. Further characterization of the mechanical properties of the carbon fiber reinforced composites revealed that, with the addition of toughening agents, the resin increased the 0° bending strength of the composites by 29.9% and the 0° compressive strength by 34.3%. Additionally, significant enhancements were observed in interlaminar shear strength and open-hole compressive strength. After the addition of TP, the compressive strength of EC3 compared to EC2 increased by 74.3% after impact, while the mode I interlaminar fracture toughness increased by 34.8% and the mode II interlaminar fracture toughness improved by 67.9%. C-scan analysis indicated that the damage area of EC3 decreased by 60.7% compared to EC2, demonstrating that the particle toughening significantly enhanced the impact resistance of the composites. The compression failure of the TP-toughened EC3 exhibited typical characteristics of kink band failure, and the micron-sized particles were able to significantly balance and absorb loads. The findings of this study indicate that resin toughening can significantly improve the 0° compressive strength of carbon fiber reinforced composites, and that the use of micron-sized toughening particles can markedly enhance the post-impact compressive strength of the composites through interlaminar toughening. This research provides insights for improving the compressive and impact resistance performance of carbon fiber reinforced composites, with implications for industrial application and guidance for further industrialization trials.

This study primarily investigates the effect of fly ash (FA) content on the mechanical properties and hydration performance of alkali-activated ground granulated blast furnace slag cements (AAGC), and compares the related properties with ordinary Portland cement (OPC). Additionally, the study examined the hydration products, thermal analysis, MIP, SEM, chemically bound water, and pH values of AAGC. The compressive strength of AAGC showed a retrogression phenomenon from 3 to 28 days, with the 14-day and 28-day compressive strengths of AAGC being higher than those of OPC. The AAGC with 20% FA content exhibits the highest 28-day compressive strength (75 MPa). The hydration heat release rate curved of OPC and AAGC can be divided into the initial induction period, induction period, acceleration period, deceleration period and steady period. As FA content increases, the 28-day pore volume of AAGC increased while pH values and chemically bound water decrease. SEM images of AAGC with low FA content showed more microcracks.