Chemiluminescence of polyethylene induced by UV irradiation

Summary The chemiluminescence (CL) of polyethylene (PE) film induced by UV irradiation was investigated. CL parameter, I₀, which indicates the oxidation rate under UV irradiation was obtained from a kinetic analysis. The I₀ was found to be valuable to evaluate the durability of PE films.     

The use of UV irradiation in polymerization

Photoinitiation is one of the most efficient methods for achieving quasi-instantaneous polymerization, transforming a liquid molecule into a solid polymer material within less than 1s. The kinetics of such ultrafast reaction can be advantageously followed by real-time infrared spectroscopy, a technique which records directly conversion versus time curves and allows evaluation of the important kinetic parameters of cross-linking polymerization. Photoinitiation has proved to be well suited to inducing frontal polymerization and achieving a deep-through cure of thick specimens. UV technology is also capable of causing fast polymerization in solid media, despite severe mobility restrictions, because of the high initiation rate provided by intense illumination. This review presents some recent advances in the UV-curing technology, special emphasis being given to the kinetic aspect of ultrafast polymerization reactions induced by light. © 1998 SCI.     

Preparation of low-density polyethylene composites by UV irradiation

Summary Composites of low-density polyethylene were prepared by the sorption of vinylic monomers and a photoinitiator into a polymer matrix, followed by UV irradiation. Gravimetric determinations showed that 2–4% incorporation of the polymer in the host matrix is possible by this method. Transmission and reflectance infrared spectra measurements showed that the vinylic polymer is lodged in the bulk of the polymer film with no surfacial deposition.     

紫外辐照交联改性UHMWPE纤维的研究

选取不同生产阶段的超高相对分子质量聚乙烯(UHMWPE)纤维进行紫外辐照交联改性,探讨了正庚烷浸泡时间、交联剂浓度、紫外辐照时间等因素对交联效果、纤维力学性能及蠕变性能的影响.结果表明:UHMWPE纤维在正庚烷中的最佳浸泡时间为48 h;紫外光最佳辐照改性时间为6 min;与初生纤维和成品纤维相比,相同改性条件下冻胶纤...     

Synthesis of biodegradable hydroxyethylcellulose cryogels by UV irradiation

Biodegradable macroporous hydroxyethylcellulose (HEC) cryogels of good quality and high gel fraction yield (95%) were synthesized via a facile method. The latter involved a relatively fast preparation of homogeneous semidilute solution of polymer and photoinitiator, (4-benzoylbenzyl)trimethylammonium chloride, followed by freezing at a defined negative temperature, an extremely short UV irradiation and subsequent thawing. HEC cryogels were successfully prepared also by using H₂O₂ as a photoinitiator. The effects of the temperature of freezing, the HEC molecular weight and the concentration of HEC solution on the cross-linking efficiency, the swelling ratio and the enzymatic degradation of HEC cryogels were investigated. Due to the cryoconcentration phenomenon, cryogels are formed at substantially low initial concentrations of the studied polymers. The highest values of gel fraction yield are achieved in the 1-2 wt.% concentration range at −20 °C. As a rule, the higher the molecular weight, the greater the gel fraction yield of the resulting cryogels. Scanning electron microscopy (SEM) analysis reveals that the interior structure of HEC cryogels is completely different from the conventional HEC hydrogels. HEC cryogels undergo decomposition by the action of cellulase enzyme, however, due to their specific morphology, the rate of degradation is slower compared to the conventional HEC hydrogel of similar gel fraction yield.     

聚砜超滤膜表面辐照改性研究

以聚砜为膜材料,聚乙二醇(PEG)为添加剂,采用浸入沉淀相转化法制备聚砜平板超滤膜,然后对实验制备的聚砜膜进行紫外辐照改性,考察了辐照对聚砜膜结构和性能的影响,研究了膜辐照前后断裂强度的变化,通过表面接触角测定仪、红外分析仪(FTIR)、扫描电镜(SEM)、改性膜的纯水通量和截留性能等方法来表征膜辐照前后的结构和性能变化.研究表明:聚砜膜断裂强度经辐照后变小,但降低幅度不大;在乙醇溶液中紫外辐照后,开始纯水通量提高而截留率降低,但降低幅度不大,时间增加到一定时通量又降低,截留率变化也不大;表面接触角随辐照时间的增长而减小,表明改性后膜表面的亲水性得到明显改善;通过FTIR分析证实在聚砜膜表面产生了新的官能团;SEM实验证实反应只发生在聚砜膜的表面而非膜内部.聚砜超滤膜经紫外辐照改性取得了良好的效果.     

紫外光辐照交联EVA的制备及表征

采用紫外辐照技术制备了交联乙烯-L酸乙烯酯共聚物(XLEVA)。研究了实验温度、实验气氛、试样厚度及辐照时间等条件以及光引发剂、光交联剂的种类和浓度等因素对凝胶含量的影响。结果表明,辐照时间为2 min,温度为100℃时,交联效果较好,在此条件下,辐照氛围及试样厚度对交联反应影响不明显。二苯甲酮的引发效果优于安息香二甲醚,三羟甲基丙烷三丙烯酸酯的助交联效果最佳,两者的最佳含量均为1%,此时XLEVA的凝胶含量可达到86.48%。     

Saccharide radicals induced by UV irradiation at room temperature

The stability of saccharide radicals induced by UV irradiation at room temperature and the ability to initiate polymerization of acrylamide were investigated. UV light of 220 < λ < 300 nm was proved to form saccharide radicals effectively at room temperature. ESR signal intensity of the irradiated saccharide was in the order of sucrose > methyl-α-D-glucopyranoside ? cellobiose > D-xylose > D-glucose α D-fructose. The saccharide radicals were fairly stable at room temperature, however, the markedly declined in amount as the samples were brought to their own melting points or allowed contact with water. When an aqueous solution of acrylamide was added to the irradiated saccharide, polymerization was initiated and the conversion increased with an increasing amount of the preirradiated saccharide. Regarding the kind of saccharide, the conversion decreased in the following order: sucrose > methyl-α-D-glucopyranoside > cellobiose > D-glucose, which indicated a good agreement with the magnitude of ESR signal intensity.     

Accelerating the crosslinking process of hyperbranched polycarbosilane by UV irradiation

A liquid hyperbranched polycarbosilane (LHBPCS) with stoichiometric C/Si ratio but without unsaturated groups was synthesized. Different from traditional thermal crosslinking, ultraviolet (UV) irradiation crosslinking was taken. The molecular weight, the consumption of SiH group and ceramic yield of LHBPCS showed an increase trend with increasing the UV irradiation time. After 30 min of UV irradiation, 71.8 wt% ceramic yield was obtained. In addition, extra divinyldimethylsilane was added into LHBPCS. Under UV irradiation, both the SiH group and vinyl group of divinyldimethylsilane were consumed. But the reaction extend of vinyl group was much faster than that of SiH group. Compared with pure LHBPCS, the mixture of LHBPCS and 5 wt% divinyldimethylsilane gave a higher ceramic yield of 79 wt% after 30 min of UV irradiation. By heating the crosslinked LHBPCS to 1000 °C, a near stoichiometric SiC ceramic was got. It exhibited excellent thermal stability at 1400 °C in air.     

借助UV光聚合制备热塑性聚氨酯–聚苯乙烯嵌段共聚物

采用端羟基的光引发剂2–羟基–2–甲基–1–苯基–1–丙酮(HMPP)封端聚氨酯预聚物,合成PUPI(一种聚氨酯大分子光引发剂),在紫外(UV)光照射下引发苯乙烯制备了聚氨酯–聚苯乙烯(PUPS)嵌段共聚物。采用实时红外、核磁共振和凝胶渗透色谱(GPC)对共聚物进行表征。通过考察苯乙烯转化率随时间的变化,发现UV光聚合可以在室温下进行。对PUPS嵌段共聚物的热力学性能和耐水性进行了研究,结果表明:聚苯乙烯链段的引入提高了聚氨酯的使用温度、拉伸强度,同时也提高了其耐水性能。     

Surface treatment of ferromagnetic nanoparticle-assembly by UV irradiation with ozone

Fe-Pt nanoparticles of 3.5 nm in average particle diameter are obtained with the simultaneous chemical reduction of platinum acetylacetonate and the thermal decomposition of iron pentacarbonyl. Because the as-synthesized particles are superparamagnetic at room temperature, they must be transformed to L1₀ ordered phase by annealing at temperatures above 773 K to apply to high-density magnetic recording media. However, the annealing at such high temperatures induces the coalescence and inter-particle sintering. In the present paper, to solve the problem caused by the annealing, we use ultraviolet-ozone treatment to modify particle surface. Even after annealing at 773 K, the crystalline size is kept at 4.4 nm. Furthermore, coercivity is higher than that without the ultraviolet-ozone treatment.     

Mechanism of photocatalytic oxidation of guanine by BiOBr under UV irradiation

This article analyzes the mechanism details of guanine photocatalytic oxidation on the surface of BiOBr nanoparticles under UV irradiation. The reaction of O₂⁻ with radical species, generated from primary oxidation of guanine by hole, is proposed to be the dominant cause of guanine damage. The present work demonstrates that BiOBr photocatalysis provided good model to investigate the reaction of substrate radical with the in situ formed O₂⁻. It also implicates that the frequently-used biomarker for DNA damage 8-oxo-7,8-dihydro-2-deoxyguanosine (8-oxodG) may be ineffective in the situation that damage is caused by O₂⁻.     

Oxidation of several chlorophenolic derivatives by UV irradiation and hydroxyl radicals

The oxidation of some chlorophenols: 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,6‐trichlorophenol, 2,3,4,6‐tetrachlorophenol, tetrachlorocatechol (3,4,5,6‐tetrachloro‐2‐hydroxy phenol) and 4‐chloroguaiacol (4‐chloro‐2‐methoxy phenol) has been studied via single photodecomposition produced by polychromatic UV irradiation, oxidation by hydroxyl radicals generated by Fenton's reagent (hydrogen peroxide plus ferrous ions), and degradation by hydroxyl radicals produced by combinations of UV irradiation plus hydrogen peroxide, and UV irradiation plus hydrogen peroxide and ferrous ions (photo‐Fenton system). These organics have been selected as models of chloro‐phenolic derivative pollutants present in wastewaters and groundwaters. The degradation levels obtained in each process are reported. The quantum yields in the single photodecomposition reaction and the rate constants between the chlorophenols and the hydroxyl radicals in the reaction with Fenton's reagent are determined. Finally, the additional contributions to the photodecomposition promoted by the radical reaction in the combined UV/H₂O₂ and photo‐Fenton systems are also evaluated. © 2001 Society of Chemical Industry     

Polymerization of acetylene derivatives induced by UV irradiation via metal carbonyls

Summary The polymerization of phenylacetylene induced by UV irradiation of W(CO)₆ in carbon tetrachloride provided in high yield a polymer, whose molecular weight reached about 80,000. The polymerization did not proceed without UV irradiation or in the absence of a halogen-donating agent such as carbon tetrachloride. On the other hand, the polymerization of 2-chloro-1-phenylacetylene was best effected by Mo(CO)₆, and did not require any halogen-donating agent (polymer MW 400,000). Polymerization of other acetylene derivatives was also examined.     

紫外辐射接枝改性UHMWPE纤维表面的研究

采用紫外辐射接枝方法对超高相对分子质量聚乙烯(UHMWPE)纤维表面进行改性。探讨了单体种类及浓度、引发剂、抗氧剂、接枝方法等对UHMWPE纤维表面处理效果的影响,测试了以其作为增强材料的复合材料的层间剪切强度。结果表明:在有氧开放体系下,气相接枝效果好于液相接枝;丙烯酰胺单体的接枝效果优于其它单体;接枝率随接枝单体浓度和接枝时间的增加而增加。采用丙烯酰胺为接枝单体,在光强度为86μW/cm~2条件下,对UHMWPE纤维进行紫外辐射接枝改性,按照一定铺层方式制备的环氧基复合材料的层间剪切强度从未处理的14.59MPa提高到17.36MPa。     

Fabrication and characterization of electrospun polybutadiene fibers crosslinked by UV irradiation

Crosslinked electrospun polybutadiene (BR) fibers were made using electrospinning and UV curing methods. The crosslinked BR fibers were obtained by irradiating UV light on the electrospun BR fibers containing a photoinitiator and a crosslinker. Although uncrosslinked electrospun BR fibers did not retain the fiber morphology at room temperature due to a cold flow resulting from the very low glass transition temperature (T_g) of BR (below ?80°C), the crosslinked electrospun BR fibers retained the fiber morphology. The crosslink density increased with increase of the content of crosslinking agent. The crosslinked BR fibers had higher T_g than the raw BR. Tensile strength, modulus, and elongation at break of the electrospun BR fiber mats increased with increase of the crosslinker content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2233–2337, 2006     

Changes in orientation caused by UV irradiation of nylon 6 fibers

The effect of UV radiation on the structural parameters that relate to the optical properties of nylon 6 fibers are investigated using interferometry. When the optical parameters are known, we can use them to calculate various orientation functions given by Hermans and de Vries. The properties of concern are the surface reflectivity, transparency, stress optical coefficient, stress due to UV irradiation, optical configuration parameter, segment anisotropy, dielectric constant, and susceptibility. The number of molecules per unit volume, isotropic refractive index, polarizability of a monomer unit, specific refractivity of the dielectric (along and across the fiber axis) and the form birefringence were obtained. The results are established by relationships designed to relate the calculated structural parameters to the time of exposure. The study demonstrates how the structural parameters change during exposure to UV radiation. Illustrations are given using graphs and microinterferograms. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3202–3211, 2003