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Thermal analysis of polyacrylonitrile (PAN) fibers is commonly employed to assess the chemical and physical changes occurring during the pre-oxidation stage. However, in actual pre-oxidation processes, PAN fibers are stretched to a certain extent (approximately 5%) to prevent fiber shrinkage. Consequently, the pre-oxidation process of PAN fiber is influenced not only by temperature and atmosphere but also by the stretching tension. In this study, two types of PAN fiber samples with different crystal structures were utilized alongside four different processing methods (PAN powder, unfixation, physical fixation, and chemical fixation) to generate three degrees of fixed stretching. These included PAN powder and unfixed PAN fiber samples (without fixation tension), physically fixed PAN fiber with relatively weak fixation tension, and chemically fixed PAN fiber with strong fixation. Through a comparison of these samples, it was observed that the fixation tension aided in preserving the crystal structure during the heating process, significantly reducing the cyclization rate of the PAN fibers. The cyclization reaction rate of PAN fiber A, initially at 85% without any fixation, decreased to 66% after physical fixation and dropped to 56% after chemical fixation. For PAN fibers with distinct crystal morphologies, the impact of the fixation tension was more prominent for PAN fibers with larger crystal sizes and lower orientation. Additionally, the presence of crystal orientation facilitated the occurrence of the cyclization reactions. [ABSTRACT FROM AUTHOR]

Linear low-density polyethylene (LLDPE) 7042, which has a butene comonomer, is widely used but has poor tear and dart strengths. For practical applications, small amounts of other materials can be blended with 7042 to effectively improve its properties. In this study, four blend resins and films (cast and compressed films) were prepared by blending 7042 with four LLDPEs (2045G, 9030, 23F, and 9085) in 8:2 ratios. The results indicated that after blending 2045G, 23F, or 9030 with 7042, the crystallization ability of the three blends was significantly suppressed and crystal size decreased. Moreover, the molecular chain can pass though more lamellar stacks in the blends, leading to an increased tie-chain concentration. Therefore, the tear and dart impact strength of the blend films improved. In contrast, the crystallization ability of the 7042/9085 blend was only slightly suppressed and did not significantly impact its properties. These findings contribute to our understanding of the relationship between material structures and properties, demonstrating that LLDPE blends can be used to improve the tear and dart strengths of 7042. KEYWORDS blends, comonomers, crystallization behavior, linear low-density polyethylene, structure and properties, tie-chain, 1 | INTRODUCTION Linear low-density polyethylene (LLDPE) is a random copolymer of ethylene and [alpha]-olefin, which is synthesized using Ziegler-Natta or metallocene catalysts. LLDPE is widely used in the polymer [...]

The production of high-performance carbon fibers relies heavily on the structural transformations of polyacrylonitrile (PAN) fiber during processing. In this article differential scanning calorimetry (DSC), synchrotron small-angle X-ray scattering (SAXS), and synchrotron wide-angle X-ray diffraction (WAXD) were used to study the changes of the thermal properties, voids and crystal structure of the PAN precursor fibers on industrial lines during the continuous processing stages, i.e., after the treatment in the coagulation bath, after stretching in boiling water and after stretching in high-temperature steam. The findings of this study suggest that after boiling water stretching the molecular chain motion of the PAN precursor fiber weaken, resulting in the expansion of the voids. After high-temperature steam stretching the voids became elliptical and oriented in the stretching direction. Although the boiling water stretching process partially damaged the (100) crystal planes of the PAN precursor fibers, it does not hinder their overall crystalline structure. The high stretching ratio primarily affected the orientation of the molecular chains. This orientation, even in the context of partial crystal plane disruption, further promoted the crystallization of the (100) crystal planes in the fibers. These experiments explored the correlation between the processing technology and fiber structure transformation of PAN-based carbon fibers, resulting in producing a guide for the preparation of high-performance carbon fibers with fewer defects. [ABSTRACT FROM AUTHOR]

Background: This study aimed to explore the incidence of occult lymph node metastasis (OLM) in clinical T1 − 2N0M0 (cT1 − 2N0M0) small cell lung cancer (SCLC) patients and develop machine learning prediction models using preoperative intratumoral and peritumoral contrast-enhanced CT-based radiomic data. Methods: By conducting a retrospective analysis involving 242 eligible patients from 4 centeres, we determined the incidence of OLM in cT1 − 2N0M0 SCLC patients. For each lesion, two ROIs were defined using the gross tumour volume (GTV) and peritumoral volume 15 mm around the tumour (PTV). By extracting a comprehensive set of 1595 enhanced CT-based radiomic features individually from the GTV and PTV, five models were constucted and we rigorously evaluated the model performance using various metrics, including the area under the curve (AUC), accuracy, sensitivity, specificity, calibration curve, and decision curve analysis (DCA). For enhanced clinical applicability, we formulated a nomogram that integrates clinical parameters and the rad_score (GTV and PTV). Results: The initial investigation revealed a 33.9% OLM positivity rate in cT1 − 2N0M0 SCLC patients. Our combined model, which incorporates three radiomic features from the GTV and PTV, along with two clinical parameters (smoking status and shape), exhibited robust predictive capabilities. With a peak AUC value of 0.772 in the external validation cohort, the model outperformed the alternative models. The nomogram significantly enhanced diagnostic precision for radiologists and added substantial value to the clinical decision-making process for cT1 − 2N0M0 SCLC patients. Conclusions: The incidence of OLM in SCLC patients surpassed that in non-small cell lung cancer patients. The combined model demonstrated a notable generalization effect, effectively distinguishing between positive and negative OLMs in a noninvasive manner, thereby guiding individualized clinical decisions for patients with cT1 − 2N0M0 SCLC. [ABSTRACT FROM AUTHOR]

Focusing on the study of the phase separation behavior of triblock copolymer and linear low-density polyethylene (LLDPE) systems helps to understand the influence of microstructure on the properties of poly(vinylcyclohexane)-b- poly(ethylene)-b-poly(vinylcyclohexane) (PVCH-PE-PVCH/LLDPE) blends. We prepared a series of blends of LLDPE and PVCH-PE-PVCH and explained their compatibility from the microstructure. The research findings indicate that despite having similar block compositions, PVCH-PE-PVCH with a higher molecular weight exhibits significantly stronger phase separation and crystallization ability compared to PVCH-PE-PVCH with lower molecular weight. In PVCH-PE-PVCH/LLDPE blends, the addition of 10 %, 20 %, and 30 % LLDPE induces earlier crystallization and crystal phase separation of polyethylene (PE) fragments. In addition, compared to the lower molecular weight of PVCH-PE-PVCH, the higher molecular weight of PVCH-PE-PVCH exhibits a higher tendency for independent crystallization and shows significant crystal phase separation during the cooling crystallization process when blended with LLDPE. The PE segments in the lower molecular weight of PVCH-PE-PVCH can more easily enter the nanoscale domain of LLDPE. Impact fracture electron microscopy also reveals better compatibility between the lower molecular weight of PVCH-PE-PVCH and LLDPE compared to the higher molecular weight of PVCH-PE-PVCH. Furthermore, the blends of lower molecular weight of PVCH-PE-PVCH and LLDPE exhibit a greater growth rate in elongation at break. [ABSTRACT FROM AUTHOR]