Influence of climatic ageing on the mechanical properties and the microstructure of low‐density polyethylene films

Blown extruded films of low‐density polyethylene (LDPE) have been subjected to climatic ageing in a sub‐Saharan facility at Laghouat (Algeria) with direct exposure to sun. Samples were characterized by complementary techniques after prescribed amounts of time up to 8 months. It was shown by tensile testing that the mechanical properties are quite sensitive to ageing: (i) the elastic modulus increases and saturates, (ii) the tensile stress increases slightly, and (iii) the rupture energy decreases dramatically after 4 months weathering. Fourier‐transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹³C NMR) were performed to identify the evolution of the polymer microstructure. The FTIR spectra reveal the initial presence of vinylidene groups that exhaust rapidly after 4 months ageing. Also, it detects the progressive multiplication of vinyl groups and oxidation products of many kinds. The NMR technique revealed specifically the carbon–carbon configurations in the polymer chains. By contrast to the original film that contained almost exclusively butyl chain branches, the aged specimens presented shorter ramifications, namely ethyl branches. Also, the presence of quaternary atoms was detected after long ageing times. The discussion of these complementary results in the light of current literature makes possible to identify the leading mechanisms that control the decay of LDPE film properties. Although these mechanisms are numerous and complex, they can be schematically summarized within three main classes: oxidation, scission, and crosslinking. Each class is discussed in details. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermo‐oxidative degradation behavior of recycled polypropylene

This study has been carried out to mimic the thermo‐oxidative degradation of polypropylene (co‐PP) during service life and recycling. Injection molded specimens were heat aged at 130°C for different times up to maximum of 300 h to simulate the degradation of co‐PP during the service life. These aged specimens were mixed with stabilizers in internal mixer and again heat aged up to 300 h. A small increase in melt flow rate (MFR) value was observed for aged co‐PP but it showed large increase after recycling. The presence of carbonyl peak at 1713 cm⁻¹ confirmed the oxidation of co‐PP during aging and it increases with aging time. Carbonyl index (CI) is increased in recycled sample with aging, whereas oxidation induction time (OIT) decreased. The stabilizers used during reprocessing are quite effective in controlling the thermo‐oxidative degradation of the polymer during processing and aging. The thermogravimetric analysis shows that the onset of degradation temperature starts at low temperature for recycled sample as compared to virgin co‐PP. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structural and photooxidation studies of poly(styrene oxide) prepared with Maghnite‐H+ as cationic catalyst

The nature of irregularities and end‐groups in poly(styrene oxide) samples prepared using Maghnite‐H⁺ as a cationic catalyst were studied by ¹H‐ and ¹³C‐NMR at 200 MHz. Head‐to‐head (H‐H) and tail‐to‐tail (T‐T) irregularities are detected in all the samples studied. Secondary hydroxyl terminal groups are identified in polymers prepared with Maghnite‐H⁺. Poly(styrene oxide) was found to undergo chain scission by aging at 25°C. It was confirmed that oxidation of this type of polymers results from the important sensitivity of the polyether soft segment to oxidative degradation. For this reason, the scissions due to the oxidation of the material lead to notable quantities of low molecular weight photoproducts. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified by MALDI‐TOF‐MS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fourier transform infrared spectroscopy study of poly(1‐trimethylsilyl‐1‐propyne) aging

The influence of various factors on the aging of poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) during long‐term storage in air was investigated with Fourier transform infrared spectroscopy. Most attention was paid to the differentiation of oxidation, the reduction of the free volume, and the absorption of low‐molecular‐weight compounds from the environment. IR spectra of PTMSP samples stored from 1–2 months to 6.5 years revealed C?O, C? O, and C? H bands that had been earlier attributed to polymer oxidation products. It was established, however, that these bands completely disappeared from IR spectra of the aged samples after their soaking in ethanol. Spectra of dried residues of ethanol extracts displayed all these bands and did not show any bands of polymer chain fragments. Gas chromatography/mass spectrometry analysis proved that the residues were composed mainly of various dialkyl phthalates. Special experiments showed that PTMSP films easily absorbed di‐n‐butyl phthalate vapors. IR spectra of the films stored for a long time showed no decrease in double‐bond and methyl group bands. It was concluded that the polymer did not undergo oxidation in air at room temperature for at least 6.5 years. The absorption of plasticizer vapors (and possibly other compounds) from the environment and the reduction of the free volume were the main reasons found for PTMSP aging. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2523–2527, 2007     

Effect of pro‐oxidants on biodegradation of polyethylene (LDPE) by indigenous fungal isolate,Aspergillus oryzae

Proxidant additives represent a promising solution to the problem of the environment contamination with polyethylene film litter. Pro‐oxidants accelerate photo‐ and thermo‐oxidation and consequent polymer chain cleavage rendering the product apparently more susceptible to biodegradation. In the present study, fungal strain, Aspergillus oryzae isolated from HDPE film (buried in soil for 3 months) utilized abiotically treated polyethylene (LDPE) as a sole carbon source and degraded it. Treatment with pro‐oxidant, manganese stearate followed by UV irradiation and incubation with A. oryzae resulted in maximum decrease in percentage of elongation and tensile strength by 62 and 51%, respectively, compared with other pro‐oxidant treated LDPE films which showed 45% (titanium stearate), 40% (iron stearate), and 39% (cobalt stearate) decrease in tensile strength. Fourier transform infrared (FTIR) analysis of proxidant treated LDPE films revealed generation of more number of carbonyl and carboxylic groups (1630–1840 cm⁻¹ and 1220–1340 cm⁻¹) compared with UV treated film. When these films were incubated with A. oryzae for 3 months complete degradation of carbonyl and carboxylic groups was achieved. Scanning electron microscopy of untreated and treated LDPE films also revealed that polymer has undergone degradation after abiotic and biotic treatments. This concludes proxidant treatment before UV irradiation accelerated photo‐oxidation of LDPE, caused functional groups to be generated in the polyethylene film and this resulted in biodegradation due to the consumption of carbonyl and carboxylic groups by A. oryzae which was evident by reduction in carbonyl peaks. Among the pro‐oxidants, manganese stearate treatment caused maximum degradation of polyethylene. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and photovoltaic properties of polythiophene derivatives with side chains containing C60 end group

A donor–acceptor double‐cable polythiophene derivative ( PT‐F1 ) with side chain containing C₆₀ end group was synthesized, and characterized by infrared, UV‐vis absorption and photoluminescence (PL) spectroscopy, and electrochemical cyclic voltammetry. Cyclic voltammogram of PT‐F1 shows the oxidation peak of the polymer main chains and the reduction peaks of the C₆₀ end groups, indicating that there is no interaction between the polymer main chains and side chain C₆₀ groups on the ground state. The UV‐vis absorption spectrum of PT‐F1 film is red‐shifted in comparison with that of its chloroform solution. The PL spectrum of the polymer main chain was quenched by the C₆₀ pendant on the side chain. Polymer solar cell with the structure of ITO/PEDOT:PSS/ PT‐F1 /Ca/Al was fabricated. The power conversion efficiency of the device based on PT‐F1 reached 0.274% under the illumination of AM 1.5, 100 mW/cm². © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

m‐Chloroaniline emulsion polymerization,macromolecular chain structure and electrochemical properties

Poly(m‐chloroaniline) (PmClAn) was synthesized by emulsion polymerization. The influences of reaction temperature and initiator concentration on polymerizations were studied. It was found that PmClAn with number‐average molecular weight of 1.85 × 10³ g mol^?1 was obtained by the following conditions: 80 °C, [monomer] = 0.187 × 10^?3 mol l^?1, [sodium lauryl sulfate] = 4.8 × 10^?2 mol l^?1, [potassium peroxydisulfate] = 5.6 × 10^?2 mol l^?1, reaction period = 2.0 h. ¹H NMR, FTIR, and transmission and scanning microscopy were used for structural characterization of PmClAn. It was shown that the ratio of benzoid to quinoid units in the macromolecular chain was respectively 3:2, and that PmClAn has a typical crystalline monoclinic form. A PmClAn molecular chain configuration was also proposed on the basis of crystallographic data. Cyclic voltammetry experiments revealed the PmClAn membrane electrode electroactivity. This electroactivity increased when the polymer was proton‐doped. When Pt particles were electrodeposited onto the polymer membrane electrode, they presented a preferred orientation. Isopropanol oxidation intensities with platinized PmClAn modified electrodes were larger than with a platinized Pt electrode. We also found that oxidation occurred mainly on the Pt particles deposited on the polymer, and that the anodic peak potential changed with polymer and its doping level. These results indicated that the Pt particles interacted with the polymer and that catalytic properties could be observed. © 2002 Society of Chemical Industry     

Extremely regio‐regular poly (3‐alkylthiophene)s from simplified chain‐growth Grignard metathesis polymerisations and the modification of their chain‐ends

A simplified route to regio‐regular poly(3‐alkylthiophene)s (P3AT) with predetermined molecular weights and low molecular weight distributions based on the chain‐growth GRIM polymerisation of 2,5‐dibromo‐3‐alkylthiophenes is detailed. It is proposed by way of in‐depth ¹³C‐, ¹H‐ and two‐dimensional NMR characterisations that the resulting P3ATs are quasi‐100% regio‐regular except for one regio‐irregular pair at one chain‐end. It is probable that chain‐end groups exhibit reduced conjugation with the rest of the polymer. A comparison of the preparation of poly(3‐hexylthiophene) and poly(3‐butylthiophene) (P3BT) is presented. New methods required for the hydrogenation, formylation and bromomethylation of the chain‐ends of P3BT, necessary to overcome its poor solubility and low reactivity, are described. Copyright © 2006 Society of Chemical Industry     

Chain transfer of vegetable oil macromonomers in acrylic solution copolymerization

The use of vegetable oil macromonomers (VOMMs) as comonomers in emulsion polymerization enables good film coalescence without the use of solvents that constitute volatile organic compounds (VOCs). VOMMs are derived from renewable resources and offer the potential of post‐application crosslinking via auto‐oxidation. However, chain transfer reactions of VOMMs with initiator and/or polymer radicals during emulsion polymerization reduce the amount of allylic hydrogen atoms available for primary auto‐oxidation during drying. Vegetable oils and derivatives were reacted with butyl acrylate and methyl methacrylate via solution polymerization, and the polymerization was monitored using in situ infrared spectroscopy to determine the extent of chain transfer. ¹H NMR spectroscopy was used to determine the loci of chain transfer and the molecular weight characteristics of the polymers were characterized by SEC. Solution polymerization was utilized because this limited temperature fluctuations and insolubility of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Controlled radical copolymerization of vinyl acetate and dibutyl maleate by iodine transfer radical polymerization

Iodine transfer radical homo‐ and copolymerization of vinyl acetate (VAc) with dibutyl maleate (DBM) were carried out in the presence of ethyl iodoacetate (EtIAc) and 2,2′‐azobis(isobutyronitrile) (AIBN) as chain transfer agent and initiator, respectively, at 60 °C. Molecular weight and its distribution and (co)polymer structure (i.e. copolymer composition and chain end groups) were analysed using gel permeation chromatography and ¹H NMR spectroscopy, respectively. Homo‐ and copolymerization reactions proceed via a controlled characteristic with predetermined molecular weight and relatively narrow molecular weight distribution. The presence of DBM in the reaction mixture decreases the consumption rate of EtIAc as well as the polymerization rate. This is attributed to the effect of DBM on the transfer constant to the EtIAc and probably on the iodine exchange rate constant between the growing chains. The effect of the concentration of AIBN, EtIAc and overall monomers on the conversion, molecular weight and its distribution was studied. Simultaneously high conversion and molecular weight with a relatively narrow molecular weight distribution can be achieved only when equimolar and intermediate concentration of EtIAc and AIBN is used in the reaction mixture. End‐group analysis by ¹H NMR reveals that iodinated VAc end groups in the (co)polymer chains are unstable, resulting in aldehyde end groups. Thermogravimetric analysis shows that the thermal stability of the VAc‐based polymer increases on incorporating DBM units into the copolymer chains. © 2013 Society of Chemical Industry     

Aging behavior and mechanism of bio‐based engineering polyester elastomer nanocomposites

Bio‐based elastomers used in industry have attracted much attention. We prepared bio‐based engineering polyester elastomer (BEE) nanocomposites by mixing bio‐based engineering polyester elastomers with carbon (CB). The CB/BEE nanocomposites were exposed to an artificial weathering environment for different time periods. Both its aging behavior changes and aging mechanism were investigated in this article. The tensile strength retention rates were each above 90% after aging at 100°C and 125°C for 72 h. CB/BEE nanocomposites exhibited good anti‐aging properties. Furthermore, the chemical changes were detected by Fourier transform infrared spectroscopy and differential scanning calorimetry. The crosslink density changes during aging of BEE were determined as well. A plausible aging mechanism of BEE was proposed. It can be concluded that the thermal oxidation process gives priority to further crosslinking in the initial period of aging. As the aging time increases, chain scission becomes the dominant element in the subsequent thermal oxidation process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40862.     

Well‐defined polymers containing 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane moiety: Synthesis,mechanism, and applications in catalysis

A series of well‐defined different chain lengths polymers, which contain the organometallic 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane core in the main chain, was obtained in one‐pot via a novel 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane (complex A )/azobisisobutyronitrile (AIBN) initiating system used in reverse atom transfer radical polymerization of styrene in different concentrations. The introduction of organotin complex A was supported by ¹H‐NMR, ¹³C–NMR, and the Inductive Coupled Plasma Emission Spectrometer analysis of the organotin‐containing polymer. Moreover, the mechanism of polymerization was investigated by changing the ratio of complex A to AIBN. It was concluded that the complex A not only acted as an important part of the initiator system but also introduced the functional organometallic group into the polymer chain. Additionally, the organotin‐containing polymer could be used as catalyst for esterification, and the reaction products' conversion could reach high up to 99% and does not decrease after four successive cycles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and nonlinear optical properties of a novel X‐type polyester containing dicyanovinylnitroresorcinoxy groups with enhanced thermal stability of dipole alignment

A novel X‐type polyester (5) containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N‐dimethylformamide and acetone. Polyester 5 shows thermal stability up to 300 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of near 108 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength is 2.99 pm V^?1. The dipole alignment exhibits thermal stability even at 7 °C above the glass transition temperature, and no significant SHG decay is observed below 115 °C due to the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. © 2013 Society of Chemical Industry     

Study on the morphology of the hydrophobically‐modified polyelectrolyte in aqueous solution by AFM measurements

This work focuses on the AFM study of the aggregation morphology and association mechanism of the hydrophobically‐association water‐soluble polymer P (AM‐AA‐BPAM) in aqueous solution. It shows that the P (AM‐AA‐BPAM) molecule chain, which has hydrophobic and hydrophilic ionic groups, forms the “spherical” aggregations as micelles below 0.2 g · dL^?1, and then connect each other to form the string‐like aggregations, which produce large viscosity for the polymer solution. It is also coincident with the FCS, DLS, and viscosity study result. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1175–1178, 2004     

Oxidation of gamma‐irradiated ultrahigh molecular weight polyethylene

Ultrahigh molecular weight polyethylene (UHMWPE), the current polymer of choice in orthopedic prosthetic devices, is typically sterilized by exposure to Co‐60 gamma irradiation prior to packaging for long‐term storage. However, the exposure to Co‐60 irradiation generates free radicals along the polymer chain that can participate in a series of reactions commencing with the oxidation of the free radicals to form reactive peroxy radicals. This study was undertaken to identify the role of hydroperoxide species in shelf‐aged and accelerated aged UHMWPE samples by using a nitric oxide derivatization technique. It is shown that the concentration of hydroperoxides did not change appreciably with shelf aging. However, during accelerated aging the hydroperoxide concentration increased to a plateau and then decreased, suggesting its role as an intermediate in the process. By contrast, the concentrations of carbonyl species continued to increase during shelf aging and accelerated aging. The effects of several packaging materials on the oxidation characteristics were also investigated. A vacuum foil package is shown to be effective in preventing oxidation to a significant extent during accelerated aging. However, accelerated aging after removal from the foil pack resulted in oxidative degradation. Extended vacuum to remove dissolved oxygen and a 5‐week room‐temperature healing process in the foil pack were shown to be ineffective in reducing oxidative degradation. It also was shown that increased moisture content in the aging environment did not affect the degradation process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2525–2542, 2000     

Effect of shear history on flow instability at capillary extrusion for long‐chain branched polyethylene

Effect of applied processing history on flow instability at capillary extrusion is studied using a commercially available low‐density polyethylene (LDPE) having long‐chain branches. It is found that processing history in an internal mixer in a molten state depresses long‐time relaxation mechanism associated with long‐chain branches, which is known as “shear modification.” Consequently, the onset of output rate for melt fracture increases greatly. Furthermore, it should be noted that the sample having intense shear history shows shark‐skin failure without volumetric distortion, although it has been believed that LDPE exhibits gross melt fracture at capillary extrusion. The reduction of elongational viscosity by the alignment of long‐chain branches along to the main chain is responsible for the anomalous rheological response. As a result, the sample shows shark‐skin failure like a linear polyethylene at a lower output rate than the critical one for gross melt fracture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanochemical degradation of an EPDM polymer

A mill-mastication study of an EPDM polymer (DuPont, Nordel 1070) was conducted in the mill-roll temperature range of 68–480°F. The extent of degradation was determined by dilute-solution viscosity measurements. The role of oxygen in the polymer mastication was followed by infrared spectroscopy. The breakdown of the EPDM polymer on the mill is minimum in the temperature range of 185–315°F. Up to 315°F. the increase in temperature leads to a decreased amount of degradation. During cold mastication mechanical breakdown occurs. The use of a free-radical acceptor shows that this type of breakdown is caused by the mechanical rupture of C? C bonds in the polymer chain. At and above 350°F. thermooxidative degradation becomes dominant, the polymer degrading drastically, and the higher the temperature, the greater the extent of degradation for the same period of mastication. Infrared spectroscopy shows that hot mastication results in decreased double-bond concentration and increased amounts of carbonyl and, possibly, anhydride and lactone groups. Of the carbonyl groups formed 30% are due to the oxidation of double bonds in terpolymer and 70% to the oxidation of the main chain. A mechanism is proposed to account for these observations.     

Degradation assessment of LDPE multilayer films used as a greenhouse cover: Natural and artificial aging impacts

This article focuses on the assessment and understanding of the mechanism of natural and artificial aging processes of a triple‐layer film made of low‐density polyethylene (LDPE) used as greenhouse cover. The film material contains color dye and ultraviolet–A (UV–A) and infrared (IR) stabilizers and antioxidant. The combined effect of temperature variations and UV–A radiations, of the natural and artificial aging, on the physical properties (free surface energy and yellow color measurements), mechanical behavior (tensile tests), thermal stability (TGA and DSC analysis), and structural stability (FTIR analysis) was investigated. The natural aging was conducted on a greenhouse, located in northern Algeria, over a period of 7 months. However, the artificial aging was performed at four different agricultural greenhouse simulating conditions of temperature and UV–A radiation (namely, at 40°C, 40°C with UV–A, 50°C, and 50°C with UV–A) for periods of aging up to 5486 h (7.6 months). The results revealed that, the maximum loss of the yellow color additives occurs at 2981 h under the natural aging process and at 2440, 1096, 1340, and 121 h under the four artificial aging conditions, respectively. There was an observed increase in the films free surface energy and a significant degradation in the mechanical properties with aging time. This can be correlated with the film material structural changes. The natural aging of the film in North Africa is almost equivalent to artificial aging at 40°C. The concurrent effect of temperature and UV–A radiations induced polymer chains scission leading to faster degradation in the film material and consequently a reduction in its durability and service lifetime. The results show also that the measured parameters are directly related to the limit of use criterion for evaluating the lifespan of agricultural greenhouse LDPE covers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An electrical approach to monitor wire and cable thermal oxidation aging condition based on carbon black filled conductive polymer composite

Polymeric materials are widely used as insulation and jacketing materials in wire and cable. When such materials are used for long‐term applications, they undergo thermal oxidation aging in the environment. It is necessary to develop an in situ and nondestructive condition monitoring (CM) method to follow the aging of cable materials. The main objective of this work was to investigate low‐density polyethylene/carbon black (LDPE/CB) conductive polymer composites as potential sensor materials for this purpose. LDPE/CB composites with a carbon black loading below the percolation threshold underwent accelerated thermal oxidation aging experiments. The results indicated that the substantial resistivity decreases of the LDPE/CB composites could be directly related to the increases in volume fraction of the conductive carbon black, which was mainly caused by the mass loss of polymer matrix and sample shrinkage during the thermal oxidation aging process. Compared to existing CM method based on density change, the electrical resistivity is more explicit regarding its absolute changes throughout the thermal oxidation aging. The change in resistivity spanned over four orders of magnitude, whereas the composite density only increased 10%. The results offer strong evidence that resistivity measurements, which reflect property changes under thermal aging conditions, could represent a very useful and nondestructive CM approach as well as a more sensitive method than density CM approach. Crystallinity changes in materials investigated by modulated DSC and TGA measurements indicated deterioration of crystalline regions in polymer during the thermal oxidation aging. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 513–520, 2004     

Synthesis and solubility properties of chitin acetate/butyrate copolymers

In this article, syntheses of chitin acetate/butyrate copolymers with different contents of acetyl residue in polymer chain have been described. Chitin copolymers as well as pure diacetylchitin (DAC) and dibutyrylchitin (DBC) have been obtained in the reaction of shrimp chitin with mixture of acetic and butyric anhydrides used in different proportion. Reactions have been carried out under heterogeneous condition with perchloric acid (PA) used as a catalyst of reaction. Chemical structure of DAC, DBC, and co‐(acetate/butyrates) was confirmed in ¹H‐NMR as well as in Fourier transform infrared (FTIR) investigations. Results of ¹H‐NMR investigation showed that in all cases of chitin esterification carried out at applied conditions, final products with summary degree of substitution (DP) closed to 2 have been obtained. Prepared chitin acetate/butyrate copolymers with high degree of polymerization (DP) (based on value of intrinsic viscosity) with varying amount of acetyl groups from 0.24 to 1.29 have been formed depending on the mixture composition of acetic and butyric acid anhydrides. All obtained co‐(acetate/butyrates) are soluble in organic solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc) as well as ethanol and form strong transparent films. It was stated that solubility of obtained chitin copolyesters slightly decreases with increase of the acetyl groups content in polymer chain, but it is still high enough to be taken into consideration for eventual production of fibers or scaffolds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011