Irradiation of poly(vinyl chlorides). Part II. Effect of dynamic mechanical properties

The dynamic Young moduli of purified PVC and PVC derivatives were measured at room temperature during the course of irradiation by ultraviolet light at 2537 A. wave-length. The PVC derivatives with copper salicylate, ferrocene, or copper phthalocyanine were prepared by Friedel-Crafts reaction as described in the previous paper. The loss tangent decreased monotonically with irradiation time, while the dynamic modulus appeared to pass through a maximum. More pronounced variations in both E and tan 6 were observed for the PVC derivatives than for the purified PVC, owing to enhanced crosslinking and scission in the presence of the substituents. The gel permeation chromatograms of irradiated PVC samples have been observed to skew to the left, where low molecular weight material occurs. The decrease in E after long exposure was discussed in terms of molecular polydispersity of the soluble fractions of PVC.     

Different photodegradation processes of PVC with different average degrees of polymerization

The influence of ultraviolet (UV)‐irradiation on the photodegradation mechanism of different average degrees of polymerization (DP ) of poly(vinyl) chloride (PVC) with UV‐irradiation time was investigated by viscosity‐average molecular weight determination, UV‐vis spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), contact angle measurement, and scanning electron microscopy (SEM). PVC films with different DP (800, 1000, 1300, 3000) were prepared by solution casting. It was carried out exposing specimens to a xenon‐arc light source with a spectral irradiance of 0.68 W/(m² ·nm) at 63°C. It was found that the photodegradation mechanism of the lower DP of PVC (DP = 1000) was different from the higher DP of PVC (DP = 3000). This was because the lower DP of PVC was a homopolymer, while the higher DP of PVC was often produced by copolymerizing with a certain quantity of crosslinking agent (e.g., DAP and DAM). UV‐vis and FTIR spectroscopy studies provided some results concerning the structure of the irradiated PVC, and the carbonyl index and C? Cl index were induced to study the process of PVC photodegradation with different DP . TGA showed that the degradation temperatures of different weight loss increased with the irradiation time. The surface morphology of the irradiated polymer films with different DP was observed by contact angle measurement and SEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crosslinking of polyvinyl chloride by electron beam irradiation in the presence of ethylene–vinyl acetate copolymer

Electron beam (EB) irradiation of polyvinyl chloride (PVC) was carried out in the presence of three different ethylene–vinyl acetate copolymers (EVA). The mechanical properties of the original and irradiated blends were tested. The gel content measurement, chlorine loss upon electron irradiation, and gel permeation chromatograph (GPC) were used to characterize the effect of EVA on the irradiation behavior of PVC/EVA blends. The content and the chemical structure of EVA in the blends had considerable effects on the mechanical properties and gel content of the blends. The incorporation of EVA into PVC blend can increase the gel content and reduce chlorine loss of the blends. The GPC analysis of the soluble part in the irradiated PVC samples showed that the addition of EVA into the PVC blend lowered the polydispersity of molecular weight of PVC. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1571–1575, 2004     

紫外光辐照对硬质聚氯乙烯结构及性能的影响

采用衰减全反射傅立叶变换红外光谱、紫外光谱、扫描电镜、凝胶渗透色谱、拉伸应力一应变、黄色指数、与水接触角及失重率等测试研究了紫外光(UV)辐照对硬质聚氯乙烯(PVC)结构及性能的影响。结果表明:随着UV辐照时间的延长,平均相对分子质量增大至最大值后,进一步延长辐照时间平均相对分子质量减小,多分散系数由1.771增加到1.919,相对分子质量分布变宽。分子链中引人了多种揣基官能团和多种共扼多烯结构。试样表面经历了粗糙、裂纹形成及其扩散等形态破坏过程,试样黄色指数由40.7%逐渐增加到90%以上,表面颜色逐渐变深,失重率逐渐增大到0.22%,与水接触角先由63.3迅速下降到55,然后下降程度趋于平缓,逐渐下降到平衡值50UV辐照的初期试样的拉伸强度由未经辐照时的55MPa增加到57MPa,进一步延长辐照时间后拉伸强度降低,而断裂伸长率由未辐照时的35.5%迅速降低到11.8%。     

超高分子量聚乙烯纤维蠕变性能改性研究

通过紫外线照射对超高分子量聚乙烯(UHMWPE)纤维进行交联改性。运用密度梯度法、声速取向测试及广角X射线衍射(WAXD)等手段测试分析了蠕变过程中纤维结晶度的变化和相变情况,并通过计算机编程对蠕变数学模型进行拟合,该方法可以快速、精确地拟合出材料的相关性能参数。拟合结果表明紫外照射处理的UHMWPE纤维普弹模量E_1略有降低,而高弹模量E_2、推迟时间τ和本体粘度η_3有一定的提高。说明紫外照射交联能改善纤维蠕变性能。     

Improvement of the photostabilization of PVC films in the presence of 2N‐salicylidene‐5‐(substituted)‐1,3, 4‐thiadiazole

The photostabilization of poly(vinyl chloride) (PVC) films by 2N‐salicylidene‐5‐(substituted)‐1,3,4‐thiadiazole compounds was investigated. The PVC films containing concentration of complexes 0.5% by weight were produced by the casting method from tetrahydrofuran (THF) solvent. The photostabilization activities of these compounds were determined by monitoring the carbonyl, polyene, and hydroxyl indices with irradiation time. The changes in viscosity average molecular weight of PVC with irradiation time were also tracked (using THF as a solvent). The quantum yield of the chain scission (ϕ_cs) of these complexes in PVC films was evaluated and found to range between 4.72 × 10⁻⁸ and 8.99 × 10⁻⁸. Results obtained showed that the rate of photostabilization of PVC in the presence of the additive followed the trend: According to the experimental results obtained, several mechanisms were suggested depending on the structure of the additive. Among them, UV absorption, peroxide decomposer, and radical scavenger for photostabilizer mechanisms were suggested. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Radiation protection of poly(vinyl chloride) by N,N-dialkyl dithiocarbamate substitution

The effect of N,N-dialkyl dithiocarbamate substitution on the radiation stability of poly(vinyl chloride) (PVC) film was studied. PVC containing 6.5–15.7 mole-% N,N-dimethyl dithiocarbamate (PDM) and PVC containing 8.3–17.5 mole-% N,N-diethyl dithiocarbamate (PDE) was irradiated with γ-rays from a Co-60 source at room temperature under vacuum. The evolved gaseous products were measured and analyzed with a mass spectrometer. The apparent G values for gas evolution of PDM and PDE decreased remarkably. For example, a G value of 0.10 was obtained for a PDE which contains 17.5 mole-% diethyl dithiocarbamate group. The mass spectrum of the evolved gas from the same PDE sample with 10-Mrad irradiation showed no hydrogen chloride to be present. The external protection was studied using polymer-blended films of PVC and PDE or PDM. The stabilization coefficients for internal protection and external protection in polymer blends were calculated. Although the ESR spectrum of the irradiated PDM, PDE, and PVDE which is synthesized by polymerization of S-vinyl-N,N-diethyl dithiocarbamate (VDE) showed the same sulfur radicals, they were different from those of the irradiated cysteamine hydrochloride and PVC containing N-methyl dithiocarbamate (PMD). From these results, the protection of a polymer by a covalently bound dithiocarbamate was discussed.     

Real‐time monitoring of laser photochemical reactions of polyvinylchloride

The formation of conjugated double bonds in polyvinylchloride (PVC) films by ultraviolet (UV) irradiation is analyzed using an in situ laser‐monitoring technique we have developed to measure changes in transmittance of thin UV‐irradiated PVC films. Conjugated polyenes of different lengths are produced by laser irradiation at 193 and 248‐nm wavelengths. This technique promises to have broader applications in the study of polymer reaction mechanisms and kinetics. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 59–63, 2000     

A study of LLDPE functionalized through ultraviolet irradiation and interfacial interaction of PA66/functionalized LLDPE blends

Some oxygen‐containing groups, such as C? O? C, C? OH, C?O, C(?O)O, and C(?O)OH, were introduced onto linear low‐density polyethylene (LLDPE) chains during ultraviolet irradiation under air, without adding any monomers and auxiliaries and without environmental pollution. After ultraviolet irradiation, the molecular weight of LLDPE decreased and its distribution became wider. The melting temperature and crystallinity of irradiated LLDPE decreased with irradiation time. The copolymer LLDPE‐g‐PA66 was formed by reaction between oxygen‐containing groups of irradiated LLDPE and amine or carboxyl end groups and amide linkage of polyamide 66 (PA66) during preparation of PA66/irradiated LLDPE blends. Compared with PA66/LLDPE blend, the mechanical properties of PA66/irradiated LLDPE blends were improved greatly because of the improved interface interaction and dispersion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Irradiation Crosslinking of PVC/ENR Blend: A Comparative Study with the Respective Homopolymers

Electron beam initiated crosslinking on a 50/50 poly(vinyl chloride)/epoxidized natural rubber blend was studied in the absence and presence of 3 phr trimethylolpropane triacrylate (TMPTA). Comparative studies were made on PVC and ENR homopolymers. The samples were irradiated by using a 3.0 MeV electron beam machine at doses ranging from 20 to 200 kGy in air and room temperature. The changes in tensile strength, gel fraction and tan δ curves of the samples were investigated. The enhancement in tensile strength, gel fraction, glass transition temperature together with a concomitant decline tan δ peak revealed that under the irradiation conditions employed, the PVC/ENR blend crosslinked by electron beam irradiation. Addition of 3 phr TMPTA found to be effective in increasing the degree of crosslinking. Similar observations were also noted for the homopolymers PVC and ENR, implying that both PVC and ENR in the blend undergo crosslinking to a certain extent.     

Effect of sands on poly(vinyl chloride) resistance to ultraviolet light

Summary Laminates made of poly(vinyl chloride) (PVC) and sands were irradiated by ultraviolet light (UV) under normal atmospheric conditions. Three different types of sand (mine, beach and river) were utilized at various concentrations levels. The effect of the sands upon flexural mechanical properties of the laminates with varying irradiation times was analyzed. It is shown that degradation induces a decrese in mechanical properties of PVC laminates but this may be prevented by adding mine sand at specific volume concentration.     

Synergistic effect of hindered amine light stabilizers/ultraviolet absorbers on the plasticized PVC during photo-irradiation

Two kinds of piperidine derivatives including a low-molecular weight (Wt. 481, T770) and a high-molecular weight (Wt. 2000–3100, C944) hindered amine light stabilizers (HALS) are added singly or with ultraviolet absorbers (UVA) in combination to plasticized poly(vinyl chloride) (PVC) samples. Digital photos, color changes, attenuated total refection-Fourier transform infrared spectra (ATR-FTIR), and mechanical properties are obtained to investigate the photostable effect of the light stabilizers on the plasticized PVC after artificial aging. PVC samples with HALS perform well at the first 400 h of irradiation in color change, FTIR, and mechanical properties, but at the last 400 h the photostability decreases. Besides, C944 performs better than T770, because C944 is a high-molecular weight UV stabilizer and has good extraction resistance. Plasticized PVC samples with UVA resist discoloring and photooxidation from the photo-irradiation. Excellent synergism is observed between the combination of HALS and UVA. PVC with HALS/UVA performs better than PVC with HALS and PVC with UVA in color differences, FTIR, and mechanical properties. The synergism is due to the different stages of functions between HALS and UVA. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of wide‐range γ‐irradiation doses on the structures and properties of 4,4′‐dicyclohexyl methane diisocyanate based poly(carbonate urethane)s

For medical applications, 4,4′‐dicyclohexyl methane diisocyanate (HMDI)‐based poly(carbonate urethane)s were synthesized from HMDI and 1,4‐butanediol as hard segments and poly(carbonate diol) (number‐average molecular weight = 2000 g/mol) as soft segments. The effects of wide‐range γ irradiation on the samples were examined through a series of analytical techniques. Scanning electron microscopy revealed that γ irradiation etched and roughened the surfaces of the irradiated samples. The gel content and crosslinking density measurements confirmed that crosslinking occurred along with degradation at all of the investigated irradiation doses and the degree of both crosslinking and degradation increased with increasing irradiation dose. Fourier transform infrared spectroscopy demonstrated that chain scission in the γ‐irradiated samples occurred at the carbonate and urethane bonds. The decreasing molecular weight and tensile strength indicated that the degradation increased with the γ‐irradiation dose. Differential scanning calorimetry and dynamic mechanical thermal analysis indicated that γ irradiation had no significant effect on the phase‐separation structures. There was a slight reduction in the contact angle. An evaluation of the cytotoxicity demonstrated the nontoxicity of the nonirradiated and irradiated polyurethanes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41049.     

低能紫外辐照聚丙烯的结构与性能

用低能紫外辐照聚丙烯,在聚丙烯分子链上引入含氧极性基团,改善聚丙烯与填料或其他工程塑料共混的相容性。通过光电子能谱（ＥＳＣＡ）、偏光显微镜、熔体流动速率（ＭＦＲ）仪、接触角和动态粘弹谱（ＤＭＴＡ）仪、毛细管流变仪等近代分析测试,研究了紫外辐照聚丙烯的结构、形态与性能。随紫外辐照时间的增加,聚丙烯的熔体流动速率增加,接触角下降。经过紫外辐照,聚丙烯的结晶形态发生了变化。对比紫外辐照聚丙烯及与绢英粉共     

Photooxidative degradation of carboxylated poly(vinyl chloride)

Thin films of poly(vinyl chloride), PVC, and carboxylated poly(vinyl chloride), C-PVC, containing 1.8% of carboxyl groups were exposed to high energy ultraviolet radiation (λ = 254 nm) in laboratory conditions. The photochemical reactions in irradiated samples were studied by FTIR and UV–Vis spectroscopy, gel permeation chromatography and gravimetric estimation of insoluble gel. It was found that photodegradation and photocrosslinking in C-PVC is accelerated, whereas photodehydrochlorination is retarded comparing to these processes in PVC. Photooxidation investigated on the base of reaction leading to formation of hydroxyl groups is also more efficient in modified PVC. However, the total amount of carbonyl groups is much lower in UV-irradiated C-PVC than that in PVC. It indicates that competitive reactions (destruction of carboxyl groups and formation of new carbonyls) occur simultaneously in C-PVC chains. The influence of carbonyl groups on photochemical processes can be explained by an efficient Norrish I and II reactions as well as by energy transfer from absorbing species to weak chemical bonds.     

Effect of the combination of a benzophenone‐type ultraviolet absorber with thermal stabilizers on the photodegradation of poly(vinyl chloride)

The effect of the combination of a UV absorber (Chimassorb 81) with different types of thermal stabilizers, including an organic calcium complex and an organotin mercaptide, on the photodegradation of poly(vinyl chloride) (PVC) was investigated by color difference measurements, UV–Vis spectroscopy, Fourier‐transform infrared spectroscopy, thermogravimetric (TG) analysis, and viscosity‐average molecular weight determination. Films of PVC containing 0.5 phr of Chimassorb 81, with and without 2 phr of a thermal stabilizer, were prepared by solution casting. Then the accelerated UV weathering of the films was carried out under xenon light with an irradiance of 0.51 W/(m² · nm) at 65°C. The results showed that both Chimassorb 81 and the mixture of Chimassorb 81 with the organic calcium complex showed good behavior in inhibiting the photodehydrochlorination and photooxidation of PVC. In contrast, the combination of Chimassorb 81 and methyltin mercaptide significantly accelerated initial color development during the final 200 h of exposure because of the UV sensitivity of the organotin. Moreover, when Chimassorb 81 and the methyltin mercaptide were used together to stabilize PVC films, the expected antioxidant effect of the mixture was not observed, in contrast to the behavior found with other stabilized systems, perhaps because the Chimassorb 81 had been depleted by the methyltin mercaptide during the UV irradiation. The TG analysis revealed that ultraviolet irradiation had caused severe destruction of the PVC chains. However, addition of Chimassorb 81 or the combination of Chimassorb 81 with the organic calcium complex effectively prevented the destruction, as was demonstrated by changes in the activation energies for thermal degradation. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Correlation between Macro- and Microstructural Changes in Ge:SiO2 and SiO2 Glasses under Intense Ultraviolet Irradiation

The photochemical transformation mechanism of defects in germanosilicate and silica glasses under ultraviolet (UV) laser irradiation has been investigated based on the changes in Raman spectra before and after irradiation. Two types of silica glasses, fused silica (type I) and dry synthetic silica (type IV), and germanosilicate optical fiber preforms were irradiated by intense UV photons from excimer lasers. Spectral changes in optical absorption and Raman spectra were examined to clarify a correlation between the microscopic defect formation and the macroscopic structural changes causing a photorefractive effect. Successive generation of E' centers through divalent centers is closely correlated with changes in Raman spectra, indicating that large structural changes in the glass network involved in this process would be the origin of photon-induced densification of the glasses. In addition, it has been proposed that the successive generation of E' centers is mediated by transient divalent centers converted from relaxed cation homobondings.     

Irradiation Modification of PVC/NBR Blend

Electron beam initiated cross-linking on the 50/50 poly(vinyl chloride), PVC/acrylonitrile butadiene rubber, NBR blend was studied in the absence and presence of 4 phr trimethylolpropane triacrylate (TMPTA). The 50/50 NBR/PVC blend was prepared by mixing in a Brabender Plasticoder at 170°C. The blend was then irradiated by using a 3.0 MeV electron beam machine at doses ranging from 0 to 200 kGy in air and room temperature. The changes in gel fraction, tensile strength, hardness, impact strength, scanning electron micrographs and dynamic mechanical properties of the samples were investigated. The gel fraction results indicate that under the irradiation conditions employed, the PVC/NBR blend cross-linked by electron beam irradiation. The addition of TMPTA was found to be effective in the acceleration of the radiation-induced cross-linking. Gradual increases in mechanical properties with irradiation dose were observed before exhibiting a decline due to embrittlement as a consequence of excessive cross-linking at higher irradiation doses. The gradual changeover from ductile to brittle fracture due to the irradiation-induced cross-linking was evident from the SEM examination The increase in the storage modulus and T_g as well as the reduction in the damping peak with the increase in irradiation dose reveal that the enhancement in mechanical properties of NBR/PVC blends upon irradiation is due to the irradiation-induced cross-linking, as well as the improved interaction between NBR and PVC.     

Photostability,thermal and mechanical properties of poly(vinyl chloride)/novel acrylate terpolymer blend

Methyl methacrylate/2‐hydroxyethyl methacrylate/maleic anhydride terpolymer with various compositions was synthesized, characterized and investigated as a photostabilizer for rigid polyvinyl chloride (PVC). The chemical structure of the terpolymer MMA/HEMA/MA, was confirmed by ultraviolet–visible and FTIR, spectroscopy. The molecular weights of the terpolymer were determined by applying gel permeation chromatography. The stabilizing efficiency of the terpolymer was evaluated by the determination of the weight loss of PVC/terpolymer blends after various irradiation times. The content of the formed gel as well as the intrinsic viscosity of the soluble fraction of the photodegraded polymer were also determined. The efficiency was also evaluated by measuring the extent of the discoloration of the photodegraded polymer. Thermal gravimetric analysis of the terpolymer and PVC/terpolymer blend were measured. Moreover, physicomechanical properties of photodegraded stabilized PVC samples were as well measured. The results revealed that the photostabilizing efficiency as well as thermal stability increased in the presence of the terpolymer as blended with PVC and by the increase of maleic anhydride ratio in the terpolymer. The photostabilizing efficiencies were compared with the industrially known UV absorber 2‐hydroxy‐4‐(octyloxy) phenylbenzophenone. J. VINYL ADDIT. TECHNOL., 25:E55–E62, 2019. © 2018 Society of Plastics Engineers     

Effect of ecofriendly grapefruit peel extract on PVC thin films photostabilizing tested under harmful weathering conditions

Exposure to ultraviolet radiation triggers a photooxidative deterioration mechanism in plastics, resulting in bond breakage, release of volatile substances, overall weight reduction, generation of free radicals, and loose crosslinking. The aim of this study was to obtain a plant extract with appropriate concentration and use it to protect polyvinyl chloride (PVC) from photodegradation. PVC films containing different concentrations of naringin that were already extracted and TINUVIN 622 as a commercial stabilizer were investigated in this paper. UV light was used to irradiate PVC films for 300 h to test the photostability. After radiation, infrared spectra, weight loss, molecular weight reduction, and surface morphology examination for PVC films were studied. In comparison to blank film, the photodegradation of PVC films was significantly reduced by the naringin and TINUVIN 622 photostabilizers. The role of photostabilizers includes deactivating excited states (as quenchers), functioning as effective light filters (pigments and absorbers), scavenging radicals, and decomposing hydroperoxides.