紫外线辐射强度对聚丙烯长丝光氧老化的影响

以聚丙烯长丝为对象,采用不同紫外线辐射强度的人工加速老化试验对其光氧老化过程进行研究.对老化过程中试样的断裂强力进行测试,并进行红外光谱分析.测试结果表明:采用2根和4根紫外荧光灯管的老化结果之间相关性较好,而与8根灯管老化结果之间的相关性较差.造成这种差别的原因在于,2根和4根灯管老化条件下的降解产物与8根灯管老化条件下的降解产物有所不同,即过高的紫外线辐射强度会导致聚丙烯长丝光氧老化动力学过程的改变.     

紫外线辐射强度对聚丙烯长丝光氧老化的影响

 以聚丙烯长丝为研究对象,采用不同紫外线辐射强度的人工加速老化试验对其光氧老化过程进行研究。对老化过程中试样的断裂强力进行测试,并进行红外光谱分析。测试结果表明：采用2根和4根紫外荧光灯管的老化结果之间相关性较好,而与8根灯管老化结果之间的相关性较差。造成这种差别的原因在于,2根和4根灯管老化条件下的降解产物与8根灯管老化条件下的降解产物有所不同,即过高的紫外辐射强度会导致聚丙烯长丝光氧老化动力学过程的改变。     

聚丙烯及聚酯纤维滤料耐紫外老化特性研究

以聚丙烯及聚酯纤维滤料为试验对象,采用UVC型紫外线辐射,进行人工老化试验,研究不同滤料紫外老化过程的性能变化。观察滤料形貌变化及纤维断裂情况,对老化过程中试样的拉伸断裂强度进行测试,并进行元素含量分析。同时,考察紫外线对箱体内的臭氧浓度的影响。测试结果表明:在一定辐射强度下,长时间紫外线辐射会导致滤料纤维的断裂降解,拉伸断裂强度下降及含氧量增加。不同滤料耐紫外线辐射的能力差异较大,造成这种差别的原因在于,滤料的材质成分及纤维直径不同。     

PVC涂层膜材料老化性能研究的进展

对PVC涂层膜材料热氧老化、光氧老化、化学降解等机理进行了简单说明,并讨论了应力对高分子材料老化的影响;系统地介绍了PVC涂层膜材料自然气候老化和人工加速老化的试验方法及相关标准,特别是光氧老化的试验方法和相关标准,以及各种宏观和微观的老化检测、分析方法,并对这些方法和相关标准加以总结和分类;分析了PVC涂层膜材料的人工加速老化试验与自然老化结果间的相关性研究现状以及存在问题;最后,对PVC涂层膜材料老化性能研究的重点方向进行了展望。     

聚氯乙烯膜材料的人工加速老化性能

以聚氯乙烯(PVC)涂层膜结构材料为对象,对其在紫外光源(4根UVB-313灯管)辐照下的人工加速老化性能进行研究。实验过程中对材料的黄度指数、力学性能进行了宏观测试,同时采用红外光谱、电镜等方法进行了微观分析。测试结果表明:随着紫外线辐照时间的增加,黄度指数逐渐上升,人工加速老化程度逐渐加深;涂层表面出现大量细小裂纹,以致于PVC涂层对基布的黏合束缚作用逐渐减少;在累积紫外辐照能达到一定程度时,膜材料的断裂伸长出现突增,但是膜材料的断裂强力基本保持不变。     

聚氯乙烯膜结构复合材料的光氧老化行为及评价

为探究经编和机织涂层膜结构复合材料的光氧老化行为,以涤纶经编和机织聚氯乙烯(PVC)涂层膜结构复合材料为对象,选取6种织物试样,研究其在紫外光辐射下的老化现象,同时与涤纶纱线力学性能的老化效应进行对比;同时研究了老化实验过程中复合材料的光氧老化行为及力学性能变化,并分析了其微观损伤机制。结果表明:涂层膜对基布纱线起到了很好的保护作用;经编织物膜结构材料老化后的初始模量均高于机织物膜结构材料,断裂强力保持率则反之;在辐射能为82.08×10³ kJ/m²时,织物的横密和纵密均为24根/(5 cm)的单面经编膜结构复合材料断裂强力保持率仅为62.4%,且其涂层对基布的保护作用已失效,涂层膜表面严重粉化和黏结;另外5种双面膜结构试样断裂强力保持率均在85%以上,在此辐射能范围内涂层面变粗糙,但仅出现少量沟槽,表现出良好的抗光氧老化性能。     

PP抗光氧老化纺粘非织物布的开发及其性能

利用ZN-P型紫外线耐气候试验机加速PP抗光氧老化纺粘布的老化过程,通过拉伸仪测试其老化实验前后的断裂强度和断裂伸长率,根据其损失率来判断抗光氧老化剂的种类、添加量及色母粒对所制备的PP纺粘布抗光氧老化性能的影响。结果表明,经阻胺类抗光氧老化剂改性的PP纺粘布,其抗光氧老化性能明显优于紫外线类抗光氧老化剂改性的PP纺粘布,当其质量分数为2%～2.2%时性价比最好。同时,色母粒的加入对PP纺粘布的抗光氧老化性能也有较大的影响。     

PP抗光氧老化纺粘非织造布的开发及其性能

利用ZN-P型紫外线耐气候试验机加速PP抗光氧老化纺粘布的老化过程,通过拉伸仪测试其老化试验前后的断裂强度和断裂伸长率,根据其损失率来判断抗光氧老化剂的种类、添加量及色母粒对所制备的PP纺粘布抗光氧老化性能的影响.结果表明,经阻胺类抗光氧老化剂改性的PP纺粘布,其抗光氧老化性能明显优于紫外线类抗光氧老化剂改性的PP纺粘布,当其质量分数为2%～2.2%时性价比最好.同时,色母粒的加入对PP纺粘布的抗光氧老化性能也有较大的影响.     

单轴多级循环加载下聚氯乙烯膜材料的力学行为与能量耗散

为研究建筑用膜材料在多级循环加载下的力学行为与能量耗散,对聚氯乙烯(PVC)膜材料进行单轴多级循环加载实验测试,分析了变形行为、能量耗散与损伤特性。研究结果表明:相对于单轴拉伸强度,经向试样的循环加卸载峰值强度较低,而纬向试样的循环加卸载强度较高;多级循环加载条件下,加载与卸载弹性模量呈现逐渐增加的变化趋势,且卸载弹性模量高于加载弹性模量;小载荷水平下,相对于经向试样,纬向试样表现出较高的总吸收应变能、弹性应变能和耗散能,但在高载荷水平下较低;在逐级循环加载过程中,PVC膜材料均表现为黏-弹-塑性,基于塑性变形累积来定义损伤变量较为合理。     

汗液老化对3种运动鞋常用材料的性能影响

对3种运动鞋常用材料进行不同时间的汗液老化处理后,测试了材料的几种物理性能.结果发现,汗液老化48 h后,对比空白组,对照组天然皮革和PVC人造革试样拉伸强度分别下降约11.3%、34.0%.PVC人造革试样断裂伸长率受汗液老化影响相对较大,在老化48 h范围内,随老化时间增加,断裂伸长率呈增加趋势,超过48 h便呈现下降趋势.汗液老化168 h后,3种材料柔软度和耐折牢度均呈下降趋势,其中PVC人造革柔软度下降较多,约11.4%.汗液老化168 h后,天然皮革里层材料变色等级为2~3级.汗液老化后,3种材料的透水汽性均有提高,其中天然皮革提高较大,约为48.6%.通过微观形态观察可以发现,汗液老化对材料表面和剖面结构产生了一定影响.     

Assessment of a mobile phone for use as a spectroscopic analytical tool for foods and beverages

A mobile phone was used to perform optical analyses of foods and beverages. The phone’s screen served as illumination source and front view camera recorded images. Reflected intensities were used to discriminate between the different samples analysed by principal component analysis. Samples studied illustrated the technique’s potential analytical capabilities with respect to adulteration and authenticity. Three coloured additives (red, green and blue) in the concentration range 2–10 mg L^?1 in a lemon lime beverage were discriminated. Adulteration by up to 25% water of milk with 3% fat content was detected with an estimated detection limit of about 3% water. Changes occurring on a green onion surface over a 48‐h ageing period at room temperature were monitored. Five different cuts from lamb carcasses weighing 9 and 14 kg were classified by the method. Considerable additional work with regard to sampling, data treatment and quantifying results is necessary before the goal of using the technique as a point‐of‐purchase analytical tool can be realised.     

Age‐related changes in pro‐opiomelanocortin (POMC) and related receptors in human epidermis

Much effort has been placed in cosmetic research for better understanding of the effects of ageing on skin’s appearance, structure, mechanical properties and function. It is now of common knowledge that UV radiations induce pre‐mature skin ageing notably in the epidermis where UV radiations induce keratinocyte differentiation. As UV radiations have also been shown to regulate the pro‐opiomelanocortin (POMC) peptide family in the skin and because no study has been conducted so far to investigate the age‐related changes in POMC and related receptors, we analysed POMC, MC‐1R, MC‐2R and MOR‐1 at mRNA level and MC‐1R, MC‐2R and MOR‐1 at protein level too in primary cultures of normal human keratinocytes obtained from female donors aged from 17 to 75 years old. Regarding the gene expressions, we observed that MC‐1R, MC‐2R and MOR‐1 suffered a dramatic decrease after 50 years of age, whereas POMC increased five‐fold. Western blot analysis confirmed these results except for MOR‐1 whose expression appeared to decrease at older age, around 70 years old. Immunostainings specific to MC‐1R, MC‐2R and MOR‐1 performed on full‐thickness skin biopsies also revealed an intense staining in the basal and spinous layers of a 30‐year‐old donor, whereas no reactivity could be observed in a 60‐year‐old one. We conclude that POMC and POMC‐related receptors suffer a dramatically disturbed balance with ageing and that this may be implicated in the general process of skin ageing.     

Modification of physico-chemical and colour parameters during the marketing of 'paté'

The evolution of different physico-chemical parameters (iodine number, TBA test, residual nitrite level, pH and moisture) and CIE L^*a^*b^* colour evolution, in pork liver ‘pate’, with and without sodium ascorbate addition, were studied.

The samples were stored in an illuminated display cabinet at different lux intensities and in the dark. The regression equations were obtained for each one of the parameters under study, from the first day of exposure to light.

The sodium ascorbate showed a protective effect on the photo-oxidation mechanism (measured by TBA test), but it did not have an influence on the samples in darkness.

In both types of paté exposed to light, fading takes place and the most important variations in colour parameters are produced during the first 24 h of exposure to light.     

EFFECTS OF BRIEF EXPOSURE OF HIGH INTENSITY ULTRAVIOLET LIGHT ON MICROBIAL SURVIVAL AND GROWTH RATES AND FORMATION OF OXIDATIVE RANCIDITY IN BEEF AT THE RETAIL LEVEL

Tissue samples of kidney adipose tissue and semitendinosis muscle were exposed to various does of UV light. Exposure times were varied from 30 to 120 s while the light intensities were varied from 200 to 4000 microwatts per cm². Naturally occurring bacterial flora and inoculum were both utilized. For all exposure times and intensities observed, no significant extension in shelf-life was noted. It appears that the exposure times and intensities used did not accelerate the formation of oxidative rancidity.     

Non-destructive method of assessing the toughness of individual Turkeys

Occasionally turkeys are exceptionally tough despite apparently normal processing, ageing, cooking etc. In an attempt to identify them under manufacturing conditions an electrical method was investigated. A potential of 14 volts a.c. (50 cycles) was applied across two points inserted in the turkey breast and the ‘Probe Reading’, or current passing, was recorded in mA. Probe Readings ?80 occurred in only about 1% of the turkeys examined. This group contained almost all the tough birds encountered, but also some 2-4 times as many tender ones. Attempts to tenderise the tough birds by increased ageing or to distinguish them by pH measurements or observations of muscular contractibility were not successful.     

Oxidative consequences of UV irradiation on isolated milk proteins: Effects of hydrogen peroxide and bivalent metal ions

β-Casein (β-CN), β-lactoglobulin (β-LG), and α-lactalbumin (α-LA), were subjected to UV irradiation, alone or in the presence of hydrogen peroxide, hydrogen peroxide plus copper, or iron. Disappearance of tryptophan (Trp) was fastest for α-LA and slowest for β-CN. Hydrogen peroxide accelerated loss of Trp, while addition of iron did not further increase the speed of Trp reduction, but the addition of copper did. Oxidation products were higher for β-CN than for β-LG following UV irradiation alone or in the presence of hydrogen peroxide or hydrogen peroxide plus iron. In the presence of copper, oxidation rates were similar for both proteins. UV photo-oxidation caused the loss of the native polypeptides, the rate of this being faster for β-LG than for β-CN. These results are compatible with the concept that formation of dityrosine and N-formylkynurenine were favoured by mobility in the native protein.     

3 种工况下PBAT/PLA材料中抗氧剂168及其降解产物的迁移

采用气相色谱-质谱法研究抗氧剂168及其降解产物从不同工况（紫外、高湿、盐雾）处理下的聚己二酸-对苯二甲酸丁二醇酯/聚乳酸（poly(butyleneadipate-co-terephthalate)/polylactic acid,PBAT/PLA）复合膜中向脂肪类食品模拟物异辛烷的迁移规律,并对每个工况下复合膜的老化程度进行力学性能以及红外光谱表征。结果表明：紫外、高湿工况对PBAT/PLA复合膜降解影响较大。紫外2 d、高湿60 d、盐雾40 d后复合膜的拉伸强度在10、15、17 MPa左右,分别下降了61.1%、41.6%、35.9%,断裂伸长率分别下降了93.5%、34.1%、21.5%。抗氧剂质量分数对复合膜性能影响不显著（P＞0.05）。物质迁移量与其在迁移实验前复合膜中的含量呈正相关。未处理的复合膜中抗氧剂168迁移量最高,为85.39 mg/kg。随着复合膜老化抗氧剂降解产物的含量增加,主要产物为三(2,4-二叔丁基苯基)磷酸酯,紫外工况下产生最多,迁移量为3.04～99.50 mg/kg。物质的迁出率受温度、含量以及复合膜老化程度三者同时影响。     

Roller extrusion of biscuit doughs

Biscuit doughs are dense solid–liquid pastes which exhibit complex rheological behaviour. The rolling behaviour of sheets of commercial short and hard biscuit doughs was investigated using an instrumented counter-rotating roll mill, which allowed the roll torque, separating force and surface pressure to be monitored. The rheological characteristics of the two doughs were quantified by analysing data from ram extrusion experiments in terms of a quasi-plastic model (following the Benbow–Bridgwater approach) and a power law fluid model. The results indicated that the doughs were not ideally suited to the quasi-plastic analysis. The power law parameters varied noticeably between the doughs but both were strongly shear-thinning (power law shear indices of 0.25 and 0.5), with large extensional viscosities. These rheological model parameters were subsequently used to generate predictions of dough behaviour during rolling. A standard sheet metal plasticity model was modified to include strain rate dependency but neither dough’s behaviour could be adequately described by this model. The power law fluid approach based on the lubrication assumption reported by Levine tended to underpredict the work requirement owing to the significant contribution from extensional deformation. Interestingly, the system could be modelled in terms of an apparent power law rheology by fitting data to Levine’s model. Better agreement was obtained for some parameters but not consistently so, indicating that the power law approach is not adequate for these soft-solid materials.