Improvement of photo-stability of LLDPE-based nanocomposites

LLDPE-based nanocomposites undergo faster photo-oxidation than the unfilled matrix and the extent of their physical properties deterioration, namely elongation at break and tensile strength, is dependent on the organo-nanoclay loading. The observed acceleration is not due to faster photo-oxidation but rather due to a reduction of the oxidation induction time. The presence in the organoclays of trace amounts of metal ions may be promoting catalytic photodegradation. While UV absorbers provide useful protection, use of a metal deactivator has been found to greatly enhance the photo-stability of the LLDPE-based nanocomposites. Combinations of a metal deactivator and UV absorber yield synergistic effects.     

EFFECTS OF ORGANIC COLORANTS ON PHOTO-INITIATED CROSSLINKING AND PHOTO-OXIDATION DEGRADATION OF POLYETHYLENE AND RELATED MECHANISM

The effects of three organic colorants on photo-initiated crosslinking and photo-oxidation degradation of polyethylene (PE) samples irradiated by microwave excited (MWE) UV lamp in the melt and the related mechanism have been studied by gel content and thermal extension rate determinations,X-ray photoelectron spectroscopy (XPS),mechanical property tests,UV spectroscopy,and light microscope.The data from the gel content and thermal extension rate determinations of photo-crosslinked polyethylene (XLPE) sam...     

Photo-oxidation and ozonization of poly(3-hexylthiophene) thin films as studied by UV/VIS and photoelectron spectroscopy

The kinetics and the mechanisms of degradation of thin P3HT layers have been investigated quantitatively for ozonization and photo-oxidation. Both, decay kinetics and product evolution of the polymer degradation are monitored by in situ UV/VIS and X-ray photoelectron spectroscopy (XPS). The degradation pathways of ozonization and photo-oxidation of P3HT turn out to be significantly different. Ozone attacks the thiophene units mainly by direct addition to the double bonds, leading to the loss of UV/VIS absorption, while the aliphatic side chains [1] are hardly affected. During photo-oxidation, the polymer is primarily attacked at the alkyl side chain which leads to the formation of reactive peroxide species. These subsequently cause the oxidation of sulfur and concomitantly the destruction of the thiophene ring, resulting in the loss of absorption. From the kinetics of the blue shift of the optical absorption it is concluded that the polymer is mainly attacked at the terminal thiophene rings the case of photo-oxidation whereas ozone attacks positions more or less randomly distributed along the chain. The rate of photo-oxidation under AM 1.5 conditions is at least one order of magnitude faster than the decomposition of P3HT by ozone.     

Photodegradation of biodegradable polyesters: A comprehensive study on poly(l-lactide) and poly(?-caprolactone)

The photodegradation of melt-crystallized and amorphous-made poly(l-lactide) (PLLA-C and PLLA-A, respectively) and cast-crystallized poly(?-caprolactone) (PCL) was investigated comprehensively for the periods up to 200 h using gel permeation chromatography, differential scanning calorimetry, tensile testing, and polarization optical microscopy. The photodegradation of PLLA and PCL films proceeds via a bulk erosion mechanism, indicating that UV penetrates the specimens with no significant reduction in its intensity, irrespective of the chemical structure and the crystallinity of biodegradable polyesters. The photodegradability of PCL chains was higher than that of PLLA chains. This strongly suggests that the chemical structure of the two sequential groups adjacent to the ester oxygen rather than the density of ester group is crucial to determine the photodegradability of biodegradable polyesters. Although PLLA chains are photodegradable even in the crystalline regions, their photodegradability is lower than that in the amorphous regions. The significant increase in weight-average molecular weight (M_w)/number-average molecular weight (M_n) was observed for PLLA-A and PCL films, even when the decrease in M_n by UV irradiation was small. Most of the tensile properties of PLLA and PCL films remained unchanged during UV irradiation, while solely the elongation at break of PCL film significantly decreased. This result reflects that among the tensile properties the elongation at break was most sensitive to the change in molecular characteristics of biodegradable polyesters by UV irradiation. The contrast between bright and dark parts of Maltese crosses remained unchanged for the spherulites in PLLA-C and PCL films even after UV irradiation for 200 h. This result exhibits that the cleaved fraction of the tie chains was too low to cause the traceable disorientation of lamellae.     

Durability prediction of p-urethane clearcoats using infrared p(hoto) a(coustic) s(pectroscopy)

The durability of topcoats is dependent on a large number of factors as polymer composition, stabilization package and the conditions during the weathering process. For obvious reasons prediction of the long-term (5-10 year) durability of coatings is very important. The rate-determining factor for the degradation of PUR coatings is photo-oxidation. The photo-oxidation rate is controlled by the polymer structure but also stabilizers as HALS has a large influence. The prediction of the durability of clearcoats is based on tracing of the photo-oxidation rate and of the HALS longevity during exposure. The photo-oxidation rate is measured using FTIR-PAS. The results show that degradation can be detected much earlier compared with classical methods as gloss loss. Moreover detection of differences between systems after short exposure times as well as prediction of the long-term durability are possible.     

Plasticizing effects of epoxidized sun flower oil on biodegradable polylactide films: A comparative study

Polylactide (PLA) is one of the most promising materials among the renewable source-based biodegradable plastics. However, high inherent stiffness and brittleness of the pure PLA is often insufficient for wide range of engineering applications. One of the best ways to improve the processability, toughness and flexibility of PLA is to plasticize with epoxidized plant oils. In this work, epoxidized sun flower oil (ESFO) was incorporated into PLA matrix. The thermal, mechanical, biodegradation, optical transmission properties and fracture morphology of ESFO plasticized PLA were investigated to make a comparison with that of PLA plasticized by commercial epoxidized soya bean oil (ESO). Results show that a remarkable improvement of elongation at break was observed in the case of ESFO incorporated PLA. Although a slightly decrease the T _g of PLA was resulted from the plasticizing effects of ESFO, the thermal stability of the plasticized PLA was improved. On the other hand, the ESFO plasticized PLA showed a higher level of UV adsorption but a lower level of biodegradation ratio. After all, ESFO exhibited similar effects on the biodegradable PLA films to ESO, which is anticipated to be a good candidate for plasticizing biodegradable polymer materials.     

Modification and Characterization of Chitosan Films Using 3-trimethoxyl Silyl Propylmethacrylate

The biodegradable flexible chitosan film was prepared by solution casting. The physico-mechanical properties, polymer loading (PL), gel content and water uptake of the chitosan film were studied. The tensile strength (TS) and % elongation at break (Eb) of the uncured chitosan film were 7.0 (MPa) and 8%, respectively. Four formulations were developed using 3-trimethoxyl silyl propylmethacrylate (TSPMA) (varied from 10–80% by weight) in methanol along with photoinitator (Darocur-1664). The raw chitosan films were then soaked in the prepared formulations and cured under UV radiation at different intensities to improve the physico-mechanical properties of the films. TS for the photocured chitosan film was 28.0 (MPa) which was 4 times higher compared to the uncured chitosan film. This TS was obtained for the formulation containing 30% silane (TSPMA) at 24th UV pass for 4 min soaking time. The maximum PL of 45.1% was obtained for the same formulation at 24th UV pass for 4 min soaking time. The water uptake and gel content of the photocured chitosan films were also studied. The scanning electron micrographs of the photocured chitosan film showed smooth surface, compact and homogeneous structure.     

Effect of the structure of the biodegradable triblock polymer polylactide-<Emphasis Type="Italic">block</Emphasis>-(polycaprolactone-<Emphasis Type="Italic">stat</Emphasis>-polylactide)-<Emphasis Type="Italic">block</Emphasis>-polylactide on its mechanical properties

The effect of the structure of the triblock biodegradable polymer synthesized from ɛ-caprolactone and L-lactide via coordination ring-opening polymerization on its mechanical properties is studied. Effects of the structure of the triblock polymer on its relative elongation at break, elastic modulus, and shape recovery after unloading are estimated by the modeling method. It is shown that the properties of the polymer in relation to its structure can be predicted. The structure-dependent characteristics of the polymers are in following ranges: relative elongation at break, 7–1500%; elastic modulus, 1–330 MPa; and shape recovery, 0–95%. The modeling data are confirmed by the back synthesis of the polymers with optimized desired characteristics.     

Effect of epoxidized palm oil on the mechanical and morphological properties of a PLA–PCL blend

In this study, the effects of epoxidized palm oil (EPO) on the mechanical and morphological properties of a blend of two types of biodegradable polymer, poly(lactic acid) (PLA) and polycaprolactone (PCL), were investigated. The solution-casting process, with chloroform as a solvent, was used to prepare samples. Addition of EPO reduced the tensile strength and modulus but increased elongation at break for the PLA–PCL blend. The highest elongation at break was observed for the blend with 10 % (w/w) EPO content. Scanning electron microscopy (SEM) indicated that the fractured surface morphology of the PLA–PCL blend became more stretched and homogeneous in PLA–PCL–EPO. Possible interactions between the PLA–PCL blend and EPO were also characterized by use of Fourier-transform infrared (FTIR) spectroscopy. Thermal stability was studied by differential scanning calorimetry and thermogravimetric analysis. The results from FTIR and SEM revealed that the miscibility of the PLA–PCL blend was improved by addition of EPO.     

热稳定剂对PVC紫外光老化过程中微观结构及宏观性能演变的影响

通过UV-Vis、FTIR、DSC、以及色差、力学性能的测试表征,实时追踪分析了在紫外光老化过程中,含Pb、Sn以及Ca-Zn热稳定剂的PVC体系微观结构和宏观性能的演变过程.结果表明,在相同光老化条件下,PVC/Pb、PVC/Sn和PVC/Ca-Zn体系的微观结构变化规律基本一致,过程中主要的化学反应是,大分子吸收光能后,发生脱HCl生成共轭双键的反应、生成羰基的氧化反应、交联反应和降解反应;不同热稳定剂的作用,主要表现在对于微观结构变化的幅度和动力学过程的影响不同.相应地,3种体系的外观色差和力学性能的变化规律也相似,但色差的变化程度和速度以及老化后力学性能的保持率因所含热稳定剂的不同而不同,其中含Sn体系的颜色稳定性最好,含Pb体系的力学性能保持率最高。     

New polymer composites based on keratin and polyethylene

New biodegradable composites based on keratin and polyethylene have been produced under shear deformation. It has been demonstrated that the introduction of keratin leads to an increase in elastic modulus and to a decrease in ultimate tensile strength and elongation at break of the compositions. Elongation at break ε_b depends on the keratin dispersity; the highest ε_b values are observed for the compositions containing the smallest keratin particles. It has been shown that the compositions are susceptible to mold fungi; i.e., they are biodegradable.     

Photo-ageing of a thermoplastic aromatic polyurethane in contact with artificial sweat

An artificial photo-ageing cell was adapted in order to study the behaviour of polymers partly immersed in artificial sweat. The goal was to select polymers and to transform them into objects that come in contact with the skin. The polymer studied in this paper is a thermoplastic aromatic polyurethane (TPU) with the following characteristics: soft, transparent, lightly yellow coloured and hypoallergenic. The ageing of this polymer was studied with or without the presence of light stabilizers, and with or without sweat. The physico-chemical changes in the TPU were analysed step by step during ageing. The differences in mass variation between the different ageing modes (with or without sweat; with or without stabilizers) provided information on the hydrolytic action of the sweat. The chemical changes that occurred around the irradiated or immersed surfaces were studied by IR-ATR spectrometry in order to characterize the photo-oxidation and hydrolytic effects as well as their coupling. The morphological modifications of the polymer were recorded by differential scanning calorimetry.     

二醋酸纤维素和聚己内酯单丙烯酸酯接枝共聚物的生物降解性能研究

通过在土壤和活性淤泥中进行生物降解的研究结果表明,二醋酸纤维素(CDA)和聚己内酯单丙烯酸酯(PCLA)的接枝共聚物(CDA-g-PCLA)在活性淤泥中的降解失重率要略高于在土壤中的降解失重率。CDA-g-PCLA的特性粘数在降解初期呈上升趋势,30 d左右达到峰值后呈下降趋势。CDA-g-PCLA和CDA随降解时间的延长,拉伸强度下降,断裂伸长率增大。     

聚酰胺6/蒙脱石纳米复合材料的紫外光老化

聚合物 /层状硅酸盐纳米复合材料的研究十分活跃 [1～ 4 ] .聚酰胺 6/蒙脱石 ( PA6/MMT)纳米复合材料与纯聚酰胺 6( PA6)相比 ,模量和强度明显提高 ,耐热性能提高尤为显著 .光氧化行为材料科学领域的重要研究课题 .Admas等 [5]报道在紫外光照射下 ,聚丙烯 /粘土纳米复合材料的氧化速度要比纯聚丙烯的快 .对于 PA6/MMT纳米复合材料的光老化研究尚未见报道 .本文以傅里叶变换红外光谱定量研究手段 ,对比分析了 PA6/MMT纳米复合材料与 PA6的紫外光氧化性能 .1　实验部分　　采用熔体插层技术 ,将 PA6( Honeywell B1 0 0 MP)和有机蒙…     

Synthesis and healing properties of poly(arylether sulfone)–poly(alkylthioether) multiblock copolymers containing disulfide bonds

Thermoplastic elastomers composed of soft and hard segments are important elastic and processable synthetic polymers. The microphase‐separated soft domains show low glass transition temperature and possess sufficient chain mobility at room temperature. In this study, we report the synthesis and healing properties of multiblock copolymers containing disulfide bonds as dynamic covalent bonds. The multiblock copolymers composed of poly(arylether sulfone) and poly(alkylthioether) segments were synthesized by oxidative coupling polymerization of the corresponding thiol‐terminated oligomers. Atomic force microscopy phase images, differential scanning calorimetry, and dynamic mechanical analysis curves indicated the microphase‐separated morphology of the multiblock copolymer. Self‐healing properties of the polymer were evaluated by changes in the elongation at break of the cut/adhered samples. The elongation recovery increased with UV irradiation time, and the multiblock copolymer showed a 93% recovery after UV irradiation for 5 h. The healing efficiency induced by UV irradiation, determined by subtracting the recovery without UV irradiation, was calculated to be 51%. According to the UV spectra and solubility changes after UV irradiation, the main healing factor in this study was the crosslinking reactions caused by thiyl radicals generated from UV irradiation instead of disulfide exchange reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3545–3553     

Photo-oxidative degradation of bisphenol A polycarbonate and its possible initiation processes

During UV degradation of bisphenol A polycarbonate (BPA-PC), photo-Fries rearrangements and photo-oxidation reactions take place, however, in outdoor exposure conditions the photo-oxidation reaction is the most dominant one. To initiate this autocatalytic oxidation process, an initiating radical is required. In this research two possible sources for photo-initiation are explored, viz. hydroperoxides and peroxides formed by thermo-oxidation and charge transfer complexes between the polymer and oxygen. A comparison of the photodegradation rate of thermo-oxidized and undegraded polycarbonate samples was made. It was shown that the formed thermo-oxidation products in BPA-PC did not affect the photo-oxidation rate. Charge transfer complexes (CTCs) between oxygen and polycarbonate were studied by UV absorption spectroscopy at different air pressures. The concentration of CTCs increased with oxygen pressures. These CTCs absorb wavelengths in the region of terrestrial sunlight and could cause the initiation of the photo-oxidation. The influence of oxygen pressure on the photodegradation of BPA-PC was studied by irradiating the samples with a by the polymer absorbing wavelength, viz. 250 nm. The absorption of this wavelength leads to photo-Fries products. It was shown that at higher oxygen pressures the rate of the photo-Fries reaction is reduced, which was explained by quenching of the photo-Fries reaction by oxygen.     

Deformation behavior and mechanical properties of hard elastic and porous films of polyethylene

Hard elastic samples of linear polyethylene were prepared by melt extrusion at a high velocity of the melt flow and by subsequent annealing of crystallized samples. The deformation behavior of hard elastic samples obtained by annealing of as-spun samples at different temperatures has been analyzed at uniaxial extension resulting in formation of porous structure. Mechanical properties of microporous films in the longitudinal and transverse directions have been investigated. Composite systems consisting of a microporous polyethylene film and a thin layer of an electroconducting polymer have been prepared. Mechanical properties of composite systems, such as elastic modulus, tensile strength, and break elongation, have been compared with the properties of polyethylene substrates.     

The photo-oxidation of EPDM rubber: Part III—Mechanistic aspects and stabilization

The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber.     

扩链法制备高分子量聚对二氧环己酮的研究

以辛酸亚锡为催化剂对对二氧环己酮单体(PDO)开环聚合合成聚对二氧环己酮(PPDO),在聚合的后期,用1,6-六亚甲基二异氰酸酯(HDI)为扩链剂进行扩链反应.研究了扩链剂用量对扩链反应的影响,加入相对于PPDO用量的0.78 wt%的HDI就能得到粘均分子量为2.35×105的PPDO.在分子量相近的情况下,扩链后产物的热稳定性和玻璃化转变温度均比未扩链的高,扩链前后的晶型没有发生变化,但结晶度大幅度降低,拉伸性能变化不大.     

Studies of pectin/polyvinylpyrrolidone blends exposed to ultraviolet radiation

The new biodegradable blends composed of natural pectin and synthetic polymer: polyvinylpyrrolidone were obtained by casting from aqueous solutions. The molecular interactions between components have been studied by FTIR. The blends were exposed to UV-irradiation and the changes in chemical structure were investigated using absorption spectroscopy (FTIR and UV-Vis). The morphology of sample surfaces before and after exposure to UV was observed by atomic force microscopy. Insoluble gel, formed as a result of photocrosslinking, was appointed gravimetrically. The relation between the blend composition and the efficiency of observed photoreactions has been considered.