Storage condition

储存条件
  • 文章类型: Published Erratum
    [这更正了文章DOI:10.3389/fbioe.2024.1354241。].
    [This corrects the article DOI: 10.3389/fbioe.2024.1354241.].
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  • 文章类型: Journal Article
    盲肠微生物群已成为改善家禽生产和福利的重要干预目标。这对于肉鸡的整体健康和性能至关重要。目前的研究集中在调查盲肠微生物移植(CMT)从健康的供体鸡的生长性能的影响,豁免权,和新孵化雏鸡的微生物组成,并评估了样品储存对盲肠样品微生物多样性的影响。一个健康的"皖南黄鸡系"被选为捐献者,来自同一品系的180只1日龄雏鸡被用作60天饲料试验的接受者。将小鸡随机分为三组(每组60只),每组重复三次。三个治疗组均为CMT-0(对照组,生理盐水溶液),CMT-I(1:12盲肠内容物,补充有10%甘油的生理盐水),和CMT-II(1:6盲肠含量,补充有10%甘油的生理盐水)。与CMT-0组相比,CMT-II组的体重增加和绝对器官重量的结果显示显着改善。与CMT-0相比,CMT-I的血清IgG水平显着提高(p<0.05)。然而,IL-6水平在CMT-I中升高,然后在CMT-II中显著降低。比较两组CMT治疗的盲肠微生物多样性,新鲜样品(FS)和在-80°C(SS)下储存的样品。结果表明,有益分类单元,例如Firmicutes和Verrucomicroota,在FS和SS中,CMT-I和CMT-II的含量均比CMT-0的含量高。水平1、2和3的微生物功能分析显示代谢改善,遗传信息处理,细胞过程,环境信息处理,以及FS和SS组的CMT-I和CMT-II中的有机系统。然而,SS组微生物多样性和功能下降。最后,盲肠微生物移植是提高肉鸡生产力和健康的一个有前途的策略。
    Cecal microbiota has emerged as a prominent intervention target for improving the production and welfare of poultry. This is essential for the overall health and performance of broiler chickens. The current study focused on investigating the effect of cecal microbiota transplantation (CMT) from healthy donor chickens on the growth performance, immunity, and microbial composition of newly hatched chicks and evaluated the effect of sample storage on the microbial diversity of the cecal samples. A healthy \"Wannan Yellow Chicken line\" was selected as the donor, and 180 1-d-old chicks from the same line were used as recipients for a 60-d feed trial. The chicks were randomly allocated to three groups (60 birds per group) with three replicates in each group. The three treatment groups were CMT-0 (control, normal saline solution), CMT-I (1:12 cecal content, normal saline supplemented with 10% glycerol), and CMT-II (1:6 cecal content, normal saline supplemented with 10% glycerol). The results of weight gain and absolute organ weight showed significant improvements in the CMT-II group compared with the CMT-0 group. Serum IgG level was significantly improved (P < 0.05) in CMT-I compared with that in the CMT-0. However, IL-6 levels increased in CMT-I and then significantly decreased in CMT-II. The cecal microbial diversity of CMT treatment was compared between two groups, fresh samples (FS) and stored samples at-80 °C (SS). The results showed that beneficial taxa, such as Firmicutes and Verrucomicrobiota, were substantially more abundant in both CMT-I and CMT-II than in CMT-0 in both FS and SS. Microbial function analysis at levels 1, 2, and 3 showed improved metabolism, genetic information processing, cellular processes, environmental information processing, and organismal systems in CMT-I and CMT-II for both FS and SS groups. However, the SS group showed decreased microbial diversity and function. To conclude, cecal microbiota transplantation is a promising strategy for enhancing the productivity and health of broiler chickens.
    The cecal microbiota refers to a diverse community of microorganisms that play a crucial role in digestion, nutrient absorption, and overall gut health, influencing the well-being and performance of the host bird. In this study, we aimed to improve the health and growth of broiler chickens by exploring a unique approach called cecal microbiota transplantation. A thorough investigation was conducted by transplanting the microbiota from healthy Wannan Yellow Chicken line donors into newly hatched chicks in a 60-d feeding trial. After dividing the chicks into three groups, each receiving different treatments, we found significant enhancements in WG and organ health in the groups that received cecal microbiota transplants. The results also showed improvements in Serum IgG levels in the treatment groups. Furthermore, the analysis of microbial diversity indicated that beneficial microorganisms were more abundant in the treated groups, suggesting a positive effect on chicken digestive health. To summarize, our findings suggest that transferring healthy gut microorganisms from mature parent chickens to young chicks can lead to improved growth, immune system function, microbial diversity, and overall health. This approach is a promising strategy for enhancing the productivity and well-being of broiler chickens.
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  • 文章类型: Journal Article
    研究海藻酸钠-魔芋葡甘聚糖(SA-KGM)膜与花色苷(LRA)和茶多酚(TP)在肉类中的功效。选择牛肉和草鱼作为代表性肉制品,在4°C下进行保鲜和新鲜度监测实验。同时,在这种受控环境中进行了薄膜的储存实验。贮藏实验结果表明,薄膜可延缓肉腐败2-4天,与空白对照相比,保存时间几乎翻了一番。此外,该薄膜具有显着的监测牛肉和草鱼腐败过程的能力。曲线拟合分析表明,薄膜的颜色变化与肉的腐败指数之间存在显着相关性。在整个胶片储存实验中,观察到水分显着影响薄膜的微观结构和结合情况,从而影响它们的机械和阻隔性能。然而,这些薄膜总体上仍然能够保持令人满意的物理化学性质。上述发现对于指导电影在食品保鲜行业中的推广至关重要。
    To investigate the efficacy of sodium alginate-konjac glucomannan (SA-KGM) films with anthocyanins (LRA) and tea polyphenols (TP) in meat, beef and grass carp were selected as representative meat products for preservation and freshness monitoring experiments at 4 °C. Concurrently, storage experiments of the films were conducted in this controlled environment. The results of the storage experiment showed that the films delayed meat spoilage by 2-4 days, nearly doubling the preservation time compared to the blank control. Additionally, the film exhibited significant capability to monitor the spoilage process of beef and grass carp. It was revealed by curve fitting analysis that there was a significant correlation between the color change of the film and the spoilage index of the meat. Throughout the storage experiment with the film, it was observed that moisture significantly influenced the microstructure and bonding situation of the films, thereby impacting their mechanical and barrier properties. However, the films were still able to maintain satisfactory physicochemical properties in general. The above findings were crucial in guiding the promotion of the film within the food preservation industry.
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  • 文章类型: Journal Article
    目的:本研究旨在评估六种结合剂在金属或陶瓷托槽和氧化锆中的结合强度和耐久性。材料与方法:六种树脂水泥粘结剂(XT,XTS,RSBU,RGBU,SBPM,和GMP)被选择用于本次调查。在进行剪切粘结强度(SBS)测试之前,将样品在37°C的蒸馏水中储存24小时或经历5,000个热循环。使用三因素方差分析和Games-Howell检验(α=0.05)对SBS数据进行统计分析。检查了粘合剂残留指数,观察了托槽和氧化锆的脱粘表面细节。结果:对于金属支架,所有组表现出临床上可接受的粘结强度,无论储存条件如何,除了XT组。关于陶瓷支架,所有组在储水24小时后显示出可接受的粘结强度。然而,在热循环之后,所有组的SBS均显着下降(p<0.05),与SBPM表现出更高的粘结强度。三因素方差分析表明,SBS值受到各因素的显著影响,并观察到三个独立变量之间的相互作用(p=0.000)。结论:与金属支架和氧化锆相比,热循环后陶瓷支架与氧化锆之间的可靠结合强度明显降低。在各种储存条件下,SBPM在陶瓷/金属支架和氧化锆之间表现出一致和强大的结合强度。此外,与本研究中使用的含HEMA的粘合剂相比,无HEMA的粘合剂显示出潜在的更一致的粘合性能。
    Objective: The present study aimed to assess the bond strength and durability of six bonding agents concerning their application to metal or ceramic brackets and zirconia. Materials and Methods: Six resin cement bonding agents (XT, XTS, RSBU, RGBU, SBPM, and GMP) were chosen for this investigation. Specimens were either stored in distilled water at 37°C for 24 h or subjected to 5,000 thermocycles before conducting a Shear Bond Strength (SBS) test. Statistical analysis of the SBS data was performed using three-way ANOVA and Games-Howell tests (α = 0.05). The Adhesive Remnant Index was examined, and the debonding surface details on brackets and zirconia were observed. Results: For metal brackets, all groups demonstrated clinically acceptable bond strength, irrespective of storage conditions, except for the XT group. Regarding ceramic brackets, all groups displayed acceptable bond strength after 24 h of water storage. However, following thermocycling, a significant decrease in SBS was noted across all groups (p < 0.05), with SBPM exhibiting a higher bond strength. Three-way ANOVA analysis indicated that SBS values were notably influenced by each factor, and an interaction among the three independent variables was observed (p = 0.000). Conclusion: The reliable bond strength between ceramic brackets and zirconia was significantly lower after thermocycling compared to that of metal brackets and zirconia. SBPM exhibited consistent and robust bond strength between ceramic/metal brackets and zirconia across various storage conditions. Furthermore, the HEMA-free adhesive demonstrated a potentially more consistent bonding performance compared to the HEMA-containing adhesive employed in this study.
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  • 文章类型: Journal Article
    滤纸交配实验广泛用于研究环境环境中质粒的结合行为和相关的抗生素抗性,然而,样品储存条件(温度和持续时间)带来的影响和偏差尚未得到系统的阐述。本研究系统地研究了标准储存条件(4℃,-20°C,-80°C)对来自污水处理厂(STP)的进水(Inf)和活性污泥(AS)样品中的质粒接合行为。研究结果表明,除了在4°C下储存1周之外,在所有测试的储存条件下,缀合效率均显著降低。值得注意的是,与-20°C相比,在-80°C下储存更有效地保持了活性污泥中的结合活性。然而,对进水样品的保存效果较差,主要由厌氧菌为主的群落组成。在4°C和-20°C下储存的流入样品中观察到IncH型质粒的系统损失。相应地,当在4°C和-20°C下储存时,随着储存时间的增加,在进水样品中检测到的携带质粒的抗性基因组基因型显示出明显的下降趋势。在活性污泥样品中观察到不相容性类型和抗性曲线方面的相对均匀的组成,无论不同的储存条件。这项研究强调了储存条件对质粒接合行为和抗性组成的关键影响,为抗性研究中的最佳样品处理提供有价值的见解。
    Filter mating experiment is widely used to study the conjugation behavior of plasmids and associated antibiotic resistance in environmental settings, however, the influence and biases brought by sample storage conditions (temperature and duration) were not yet systematically elaborated. This study systematically investigated the influence of standard storage conditions (4 °C, -20 °C, -80 °C) on plasmid conjugation behavior in influent (Inf) and activated sludge (AS) samples from sewage treatment plants (STP). The findings revealed a significant reduction in conjugation efficiency under all the tested storage conditions except for 1-week storage at 4 °C. Notably, storing at -80 °C maintained conjugation activities in activated sludge more effectively compared to -20 °C. However, the preservation performance was less effective for influent samples, which consist mainly of anaerobe-dominant communities. Systematic loss of IncH-type plasmids was observed in influent samples stored at 4 °C and -20 °C. Correspondingly, the plasmid-carrying resistome genotypes detected in the influent samples showed a clear downward trend with the increase in storage duration when stored at 4 °C and -20 °C. A relatively uniform composition in terms of incompatibility type and resistome profile was observed across activated sludge samples, regardless of the varied storage conditions. This study highlights the critical impact of storage conditions on plasmid conjugation behavior and resistome composition, offering valuable insights for optimal sample handling in resistome research.
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  • 文章类型: Journal Article
    背景:对具有长保质期且便于烹饪的预煮面条产生了极大的兴趣。然而,制备过程中的热过程以及它们的高水分含量可导致在储存过程中显著的质量劣化。然而,尚未对这些质量损失进行全面评估。
    结果:不同储存温度(25oC,4oC,和-20oC)主要从水动力学和结构角度阐明了预煮米粉的回生相关物理化学变化。热分析表明,在冷藏温度下储存的面条中明显发生了支链淀粉重结晶。其次是室温。冷藏加速了淀粉的回生,导致水分子被截留在晶体结构中,通过降低预煮面条的水水合性能和加权T2弛豫时间。这些水迁移模式与面条的质地变化(更高的硬度和Rmax/延展性)相关。此外,在冷藏面条的层析成像和显微图像中观察到淀粉回生导致的更高的结构密度和厚度。主成分分析表明,预煮面条在贮藏过程中的各种理化变化与淀粉回生程度高度相关(r>0.83)。
    结论:在冷藏条件下储存的预煮面条的物理化学特征与水的分子动力学密切相关,表明淀粉回生引起的水流动性显着降低,因此,这有助于它们的热量,断层摄影术,和纹理变化。本文受版权保护。保留所有权利。
    BACKGROUND: There has been significant interest in pre-cooked noodles that have a long shelf life and are convenient to cook. However, the thermal processes during preparation, and their high moisture content, can lead to significant quality deterioration during storage. Nevertheless, a comprehensive evaluation of these quality losses has not yet been conducted.
    RESULTS: The effects of different storage temperatures (25, 4, and -20 °C) on the retrogradation-related physicochemical changes in pre-cooked rice noodles were elucidated mainly from the water dynamics and structural viewpoints. Thermal analysis demonstrated that amylopectin recrystallization took place in the noodles stored at refrigerated temperature, followed by room temperature. The refrigerated storage accelerated the starch retrogradation that caused the water molecules to become entrapped within the crystalline structure by lowering the water hydration properties and weighted T2 relaxation times of the pre-cooked noodles. These water mobility patterns were correlated with the textural changes in the noodles (greater hardness and Rmax /extensibility). Furthermore, the higher structural density and thickness derived from starch retrogradation were observed in the tomographic and microscopic images of the refrigerated noodles. The principal component analysis demonstrated that various physicochemical changes of the pre-cooked noodles during storage showed high correlations with the degree of starch retrogradation (r > 0.83).
    CONCLUSIONS: The physicochemical features of the precooked noodles stored under refrigerated conditions were involved in the molecular dynamics of water, showing a notable water mobility reduction derived from the starch retrogradation, which contributed to their thermal, tomographical, and textural changes. © 2023 Society of Chemical Industry.
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  • 文章类型: Video-Audio Media
    背景:研究人类肠道病毒对肠道细菌群落的影响及其对健康或疾病轨迹的假定影响的兴趣越来越大。大多数肠道病毒学研究是基于储存的粪便样品的测序。然而,对于常规的储存缓冲液和储存条件如何影响噬菌体的感染性和影响下游metavirome测序,人们知之甚少。
    结果:我们证明了不同加标噬菌体(T4,c2和PhiX174)的感染性和基因组回收率是可变的,并且高度依赖于存储缓冲液。无论储存温度和时间如何,所有测试的噬菌体立即失去其感染性的100%(DNA/RNAShield)或超过90%(StayRNA和RNAlater)。一般来说,在SM缓冲液中在4°C下将噬菌体感染性保存长达30天,并将噬菌体DNA完整性保持长达100天。在帆布,最有效的缓冲,所有掺入的噬菌体基因组保存至少100天.在-80°C下延长的储存时间(500天)在不同缓冲液中不同地影响病毒多样性。保存在CANVAX或DNA/RNAShield缓冲液中的样品在metavirome组成中的变化最小,经过长时间的储存,但他们产生了更多被归类为“无特征”的重叠群。此外,与SM缓冲区相比,这些储存缓冲液在metavirome测序文库中产生了更高比例的细菌DNA.我们证明了后者是由于在病毒提取过程中用于去除细胞外DNA的DNA酶的失活。后者可以通过在病毒提取之前采用额外的洗涤步骤来部分避免。
    结论:粪便样品储存缓冲液和储存条件(时间和温度)强烈影响噬菌体感染性和病毒组成,如通过噬斑测定和metavirome测序所确定的。缓冲液的选择对病毒序列和分析的质量比储存温度和储存时间具有更大的影响。基于这些结果,我们建议在4°C的SM缓冲液中储存粪便病毒样品,以分离病毒,如果实际可行,则在-80°C的宏基因组应用(即,进入冷库)。对于储存在其他缓冲液中的粪便样品,在病毒提取和测序之前,应清除样品中的这些缓冲液。视频摘要。
    There is an increasing interest in investigating the human gut virome for its influence on the gut bacterial community and its putative influence on the trajectory towards health or disease. Most gut virome studies are based on sequencing of stored fecal samples. However, relatively little is known about how conventional storage buffers and storage conditions affect the infectivity of bacteriophages and influence the downstream metavirome sequencing.
    We demonstrate that the infectivity and genome recovery rate of different spiked bacteriophages (T4, c2 and Phi X174) are variable and highly dependent on storage buffers. Regardless of the storage temperature and timespan, all tested phages immediately lost 100% (DNA/RNA Shield) or more than 90% (StayRNA and RNAlater) of their infectivity. Generally, in SM buffer at 4 °C phage infectivity was preserved for up to 30 days and phage DNA integrity was maintained for up to 100 days. While in CANVAX, the most effective buffer, all spiked phage genomes were preserved for at least 100 days. Prolonged storage time (500 days) at - 80 °C impacted viral diversity differently in the different buffers. Samples stored in CANVAX or DNA/RNA Shield buffer had the least shifts in metavirome composition, after prolonged storage, but they yielded more contigs classified as \"uncharacterised\". Moreover, in contrast to the SM buffer, these storage buffers yielded a higher fraction of bacterial DNA in metavirome-sequencing libraries. We demonstrated that the latter was due to inactivation of the DNases employed to remove extra-cellular DNA during virome extraction. The latter could be partly avoided by employing additional washing steps prior to virome extraction.
    Fecal sample storage buffers and storage conditions (time and temperature) strongly influence bacteriophage infectivity and viral composition as determined by plaque assay and metavirome sequencing. The choice of buffer had a larger effect than storage temperature and storage time on the quality of the viral sequences and analyses. Based on these results, we recommend storage of fecal virome samples at in SM buffer at 4 °C for the isolation of viruses and at - 80 °C for metagenomic applications if practically feasible (i.e., access to cold storage). For fecal samples stored in other buffers, samples should be cleared of these buffers before viral extraction and sequencing. Video Abstract.
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  • 文章类型: Journal Article
    牡丹是一种重要的木本油料作物,主要是异花授粉。然而,低产已成为制约奥氏石竹产业发展的重要因素。异花授粉已成为提高种子产量的重要措施之一。因此,保存具有高活力的花粉对于确保P.ostii的成功授粉至关重要。在这项研究中,我们发现了一个有效的方法系统来评估可行性,发芽能力,和紫苏花粉粒的最佳贮藏条件。体外最佳培养基为50g/L蔗糖,100mg/L硼酸,50g/LPEG6000,100mg/L硝酸钾,300毫克/升硝酸钙,和200mg/L硫酸镁,pH为5.4。在25°C下达到体外最佳发芽条件120分钟,便于观察花粉管的发芽率和长度。此外,通过比较9种染色方法来评估花粉粒的活力。其中,MTT,TTC,联苯胺-H2O2和FDA有效区分有活力和无活力的花粉,FDA染色方法的结果与离体花粉发芽率相似。在评估花粉储存后,解冻和复水实验表明,4℃解冻30分钟,25℃复水30分钟可提高低温贮藏花粉粒的发芽率。低温贮藏试验表明,4℃适宜于梭菌花粉粒的短期贮藏,而-80°C适合长期储存。这是关于体外萌发的第一份报告,生存能力测试,和假单胞菌花粉粒的储存,这将为奥斯蒂种质保护和人工授粉提供有用的信息。
    Paeonia ostii is an important woody oil crop mainly cross-pollinated. However, the low yield has become an important factor restricting the industrial development of P. ostii. Cross-pollination has become one of the important measures to increase the seed yield. Therefore, conservation of pollen with high vitality is crucial to ensure successful pollination of P. ostii. In this study, we found an effective methodological system to assess the viability, ability to germinate, and optimal storage conditions of P. ostii pollen grains. The optimal medium in vitro was 50 g/L sucrose, 100 mg/L boric acid, 50 g/L PEG6000, 100 mg/L potassium nitrate, 300 mg/L calcium nitrate, and 200 mg/L magnesium sulfate at pH 5.4. Optimal germination condition in vitro was achieved at 25 °C for 120 min, allowing easy observation of the germination percentage and length of the pollen tubes. In addition, the viability of pollen grains was assessed by comparing nine staining methods. Among them, MTT, TTC, benzidine-H2O2, and FDA were effective to distinguish between viable and non-viable pollen, and the results of the FDA staining method were similar to the pollen germination percentage in vitro. After evaluation of pollen storage, thawing and rehydration experiments showed that thawing at 4 °C for 30 min and rehydration at 25 °C for 30 min increased the germination percentage of pollen grains stored at low temperatures. The low-temperature storage experiments showed that 4 °C was suitable for short-term storage of P. ostii pollen grains, while -80 °C was suitable for long-term storage. This is the first report on the in vitro germination, viability tests, and storage of P. ostii pollen grains, which will provide useful information for P. ostii germplasm conservation and artificial pollination.
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  • 文章类型: Journal Article
    Tengkawang黄油是一种来自婆罗洲的土著和传统黄油,可以成为制药和食品应用的脂质来源。研究发现,腾卡旺黄油是一种更便宜的可可脂替代品,而不会影响其质量。然而,目前的存储方法仍然非常传统,导致腾卡王黄油变质更快。本研究旨在通过Arrhenius模型和腾卡旺黄油氧化稳定性指数分析来计算和评估储存动力学模型。在-5、5、24和60°C的温度下进行储存条件,以预测腾卡旺黄油储存动力学模型。添加抗氧化剂如抗坏血酸,生育酚,木质素和腾卡旺黄油有助于提高氧化稳定性指数。腾卡旺黄油酸度和过氧化物模型的动力学遵循零级反应,活化能值分别为11.139kJmol-1和12.320kJmol-1。酸度的预测模型为酸度=4.417-7.903texp(-11,139/RT),过氧化物的模型为过氧化物=2.155-10.998texp(-12,320/RT)。腾卡旺黄油在22°C时的氧化稳定性指数值和温度升高十度时的氧化速率(Q10),tengkawang黄油与抗坏血酸,腾卡旺黄油与生育酚,含木质素的腾卡旺黄油分别为66,896和2.815;224,680和1.993;106,120和2.725;81,658和2.961。动力学和氧化稳定性指数模型数据可作为腾卡旺黄油制品贮藏保鲜的参考。
    Tengkawang butter is an indigenous and traditional butter from Borneo that can be a lipid source for pharmaceutical and food applications. Studies found that Tengkawang butter is a cheaper cocoa butter substitution without compromising its quality. However, the current storage method is still very traditional, resulting in faster deterioration of Tengkawang butter. This study aims to calculate and evaluate the storage kinetics model with the Arrhenius model and the tengkawang butter oxidation stability index analysis. Storage conditions were carried out at temperatures of -5, 5, 24, and 60 °C to predict the tengkawang butter storage kinetics model. The addition of antioxidants such as ascorbic acid, tocopherol, and lignin to tengkawang butter help increase the oxidation stability index. The kinetics of the tengkawang butter acidity and peroxide models followed a zero-order reaction with activation energy values of 11.139 kJ mol-1 and 12.320 kJ mol-1, respectively. The prediction model for acidity is Acidity = 4.417-7.903t exp (-11,139/RT), and the model for peroxide is peroxide = 2.155-10.998t exp (-12,320/RT). The oxidation stability index values at 22 °C and the rate of oxidation when the temperature rises by ten degrees (Q10) of tengkawang butter, tengkawang butter with ascorbic acid, tengkawang butter with tocopherol, and tengkawang butter with lignin were 66,896 and 2.815; 224,680 and 1.993; 106,120 and 2.725; 81,658 and 2.961, respectively. The kinetic and oxidation stability index model data can be used as a reference for storage and preserving products made from tengkawang butter.
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  • 文章类型: Journal Article
    聚酰胺酸(PAA)是聚酰亚胺(PI)的前体,其溶液性能直接影响PI树脂的最终性能,电影,或纤维。PAA溶液随时间的粘度损失是臭名昭著的。有必要基于除粘度以外的分子参数随储存时间的变化,对溶液中PAA的降解机理进行稳定性评估和揭示。在这项研究中,通过4,4'-(六氟异丙烯)二邻苯二甲酸酐(6FDA)和4,4'-二氨基-2,2'-二甲基联苯(DMB)在DMAc中的缩聚制备PAA溶液。通过测量分子参数,系统地研究了在不同温度(-18,-12,4和25°C)和不同浓度(12wt%和0.15wt%)下储存的PAA溶液的稳定性,包括Mw,Mn,Mw/Mn,Rg,和[η],在流动相0.02MLiBr/0.20MHAc/DMF中使用凝胶渗透色谱法与多个检测器(GPC-RI-MALLS-VIS)偶联。浓缩溶液中PAA的稳定性下降,如Mw从0%的降低率所示,7.2%,从34.7%到83.8%,锰从0%,4.7%,和30.0%到82.4%,随着温度从-18,-12和4到25°C的升高,分别,储存后139天。浓缩溶液中PAA的水解在高温下加速。值得注意的是,在25°C,稀释的溶液比浓缩的溶液稳定得多,并且在10小时内表现出几乎线性的降解速率。Mw和Mn迅速下降了52.8%和48.7%,分别,在10小时内。这种更快的降解是由稀释溶液中更大的水比率和更少的链缠结引起的。本研究中(6FDA-DMB)PAA的降解没有遵循文献报道的链长平衡机制,考虑到Mw和Mn在储存过程中同时下降。
    Polyamic acid (PAA) is the precursor of polyimide (PI), and its solution\'s properties have a direct influence on the final performances of PI resins, films, or fibers. The viscosity loss of a PAA solution over time is notorious. A stability evaluation and revelation of the degradation mechanism of PAA in a solution based on variations of molecular parameters other than viscosity with storage time is necessary. In this study, a PAA solution was prepared through the polycondensation of 4,4\'-(hexafluoroisopropene) diphthalic anhydride (6FDA) and 4,4\'-diamino-2,2\'-dimethylbiphenyl (DMB) in DMAc. The stability of a PAA solution stored at different temperatures (-18, -12, 4, and 25 °C) and different concentrations (12 wt% and 0.15 wt%) was systematically investigated by measuring the molecular parameters, including Mw, Mn, Mw/Mn, Rg, and [η], using gel permeation chromatography coupled with multiple detectors (GPC-RI-MALLS-VIS) in a mobile phase 0.02 M LiBr/0.20 M HAc/DMF. The stability of PAA in a concentrated solution decreased, as shown by the reduction ratio of Mw from 0%, 7.2%, and 34.7% to 83.8% and that of Mn from 0%, 4.7%, and 30.0% to 82.4% with an increase of temperature from -18, -12, and 4 to 25 °C, respectively, after storage for 139 days. The hydrolysis of PAA in a concentrated solution was accelerated at high temperatures. Notably, at 25 °C, the diluted solution was much less stable than the concentrated one and exhibited an almost linear degradation rate within 10 h. The Mw and Mn decreased rapidly by 52.8% and 48.7%, respectively, within 10 h. Such faster degradation was caused by a greater water ratio and less entanglement of chains in the diluted solution. The degradation of (6FDA-DMB) PAA in this study did not follow the chain length equilibration mechanism reported in literature, given that both Mw and Mn declined simultaneously during storage.
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