Rigid polyisocyanurate–waterglass foam composite: Preparation,mechanism, and thermal and flame‐retardant properties

A rigid polyisocyanurate–waterglass foam (PIWGRF) composite was prepared with polyaryl poly(methylene isocyanate) and waterglass (WG) as the main materials; water as a blowing agent, and no polyols. We speculated the formation mechanism of the PIWGRFs on the basis of the analysis of experiment data, scanning electron microscopy characterization, and transmission electron microscopy. The results show that three‐dimensional nanoflakes derived from the cured WG was observed; this was connected with polyisocyanurate by secondary bonding (Si? O? H?N). Thermogravimetric testing indicated that the thermal stability and residual mass (34%) of the PIWGRFs were significantly higher than those of rigid traditional polyurethane foams (T‐PUFs). When the core density of the PIWGRFs was 32.6 kg/m³, the strength was up to 162.9 KPa by excessive filling. The flame retardancy of the PIWGRFs, including the time to ignition, heat‐release rate, total smoke of release, and limiting oxygen index, was obviously better than that of the T‐PUFs. The structure of the residual char was more dense and orderly; this was also an effective barrier layer. The reason was attributed to the fact that the WG did not contain combustible elements. So, the PIWGRFs had excellent thermal stability, flame retardancy, and environmental friendliness. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46182.     

Spatial Heterogeneity of Thermo‐Oxidative Degradation in Impact Poly(propylene) Copolymers

The spatial degradation in impact PP copolymers with different ethylene contents is studied by FTIR microscopy and layer‐by‐layer milling of the sample surfaces, followed by ATR‐FTIR, SEC, and CRYSTAF analysis. FTIR allows for tracking of the rate of degradation, providing information on the depth profiling of the degradation. Results show that samples with lower ethylene content degrade faster at all depths than those with higher ethylene content. The latter show a more uniform degradation from the surface to the bulk of the material at longer degradation times. This is ascribed to the higher amorphous content which results in a larger oxygen diffusion to the centre of the material while its slower rate of degradation is ascribed to the lower tertiary carbon content.

     

Micropatterning of polymethacrylates by single‐ or two‐photon irradiation using π‐conjugated o‐nitrobenzyl ester phototrigger as side chains

A new single‐/two‐photon sensitive monomer, (E)‐5‐(4‐ethoxystyryl)?2‐nitrobenzyl methacrylate (ENbMA), was synthesized and copolymerized with methyl methacrylate (MMA) to form a series of photosensitive copolymers P(ENbMA–MMA)s that were well characterized by ¹H NMR and GPC. The photochemical and photophysical properties of both photosensitive monomer and copolymers upon visible light irradiation were studied by UV–Vis, FTIR, and HPLC spectra, which confirmed that 5‐(4‐ethoxystyryl)‐2‐nitrobenzyl ester can be photolyzed effectively with generation of the corresponding 5‐(4‐ethoxystyryl)‐2‐nitrosobenzaldehyde and carboxylic acid groups. The successful photocleavage endowed the optimized copolymers with excellent micropatterning property due to the effective generation of alkaline‐soluble carboxylic acid groups. Moreover, the high two‐photon absorption cross‐sections (over 20 GM at 800 nm) and the comparable photolysis upon two‐photon NIR light irradiation of the chromophores provided the copolymers with significant application in two‐photon microfabrication. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4099–4106, 2013     

Preparation and properties of polystyrene‐g‐poly(butyl acrylate) copolymer emulsions with ultrasonic radiation. I. Preparation technology and coagulum ratio

A stable emulsion of polystyrene‐g‐poly(butyl acrylate) was prepared via the following steps: (1) foam polystyrene waste was dissolved in butyl acrylate; (2) the solution was added to an aqueous solution of sodium dodecyl sulfate, ammonium persulfate, and sodium hydrogen bicarbonate; and (3) the mixture was emulsified and graft‐copolymerized by ultrasonic radiation and agitation. Then, the effects of various factors, such as the strength and time of the ultrasonic radiation, the type and dosage of the emulsifier, the concentrations of the initiator and butyl acrylate, the quantity of acrylic acid, and the reaction temperature, on the coagulum ratio were investigated and analyzed. As a result, a suitable technology for reducing the amount of coagulum could be proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1405–1409, 2005     

Degradation of poly(D,L‐lactic acid)‐b‐poly(ethylene glycol) copolymer and poly(L‐lactic acid) by electron beam irradiation

This article investigated the effects of electron beam (EB) irradiation on poly(D ,L ‐lactic acid)‐b‐poly(ethylene glycol) copolymer (PLEG) and poly(L ‐lactic acid) (PLLA). The dominant effect of EB irradiation on both PLEG and PLLA was chain scission. With increasing dose, recombination reactions or partial crosslinking of PLEG can occur in addition to chain scission, but there was no obvious crosslinking for PLLA at doses below 200 kGy. The chain scission degree of irradiated PLEG and PLLA was calculated to be 0.213 and 0.403, respectively. The linear relationships were also established between the decrease in molecular weight with increasing dose. Elongation at break of the irradiated PLEG and PLLA decreased significantly, whereas the tensile strength and glass transition temperature of PLLA decreased much more significantly compared with PLEG. The presence of poly(ethylene glycol) (PEG) chain segment in PLEG was the key factor in its greater stability to EB irradiation compared with PLLA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A strategy for the preparation of closed‐cell and crosslinked polypropylene foam by supercritical CO2 foaming

We report the preparation of a closed‐cell polypropylene (PP) foam material by supercritical carbon dioxide foaming with the assistance of γ‐ray radiation crosslinking. Styrene–ethylene–butadiene–styrene (SEBS) copolymer was added to PP to enhance radiation crosslinking and nucleation. Radiation effects on the foaming of the PP/SEBS blend with different ratios were investigated. A significant improvement in the foaming of the crosslinked PP/SEBS blend was achieved as compared to pristine PP. The cell density of the crosslinked PP/SEBS foam greatly increased at a dose of 10 kGy and a high closed‐cell ratio was obtained. The tensile strength of the crosslinked PP/SEBS foams (10 kGy) was improved from 14 to 20.7 MPa compared to pristine PP foam (0 kGy). In addition, the crosslinked PP/SEBS blend exhibited a wider foaming temperature window (10 °C) as compared to the non‐crosslinked ones (4 °C). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45809.     

The effect of pH on the hydrolytic degradation of poly(ε‐caprolactone)‐block‐poly(ethylene glycol) copolymers

The in‐vitro hydrolytic behavior of diblock copolymer films consisting of poly(ε‐caprolactone) (PCL) and poly(ethylene glycol) (PEG) was studied at pH 7.4 and pH 9.5 at 37°C. The degradation of these films was characterized at various time intervals by mass loss measurements, GPC, ¹H‐NMR, DSC, FTIR, XRD, and SEM. A faster rate of degradation took place at pH 9.5 than at pH 7.4. Analysis of the molecular weight profile during the course of degradation revealed that random chain scission of the ester bonds in PCL predominates at the initial induction phase of polymer degradation. There was also an insignificant mass loss of the films observed. Mass spectroscopy was used to determine the nature of the water soluble products of degradation. At pH 7.4, a variety of oligomers with different numbers of repeating units were present whereas the harsher degradation conditions at pH 9.5 resulted in the formation of dimers. From the results, it can be proposed that a more complete understanding of the degradation behavior of the PCL‐b‐PEG copolymer can be monitored using a combination of physiological and accelerated hydrolytic degradation conditions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical stability of high‐molecular‐weight polyacrylamides and an (acrylamido tert‐butyl sulfonic acid)–acrylamide copolymer used in enhanced oil recovery

High‐molecular‐weight partially hydrolyzed and sulfonated polyacrylamides are widely used in enhanced oil recovery (EOR). Nonionic polyacrylamide and polyacrylamide‐based microgels are also used in water shut‐off treatments for gas and oil wells. A comparative study of the mechanical degradation for three linear polyacrylamides and a microgel is presented. Mechanical degradation is quantified from the loss of the viscosity of the polymer solution as it passes through a stainless steel capillary with a length of 10 cm and an internal diameter of 125 µm. The critical shear rate above which degradation increases exponentially was found to depend on the chemical structure of the polymer, molecular weight, and electrolyte strength. The nonionic polyacrylamide shows higher degradation and lower critical shear rate compared with a sulfonated polyacrylamide with similar molecular weight. Moreover, the nonionic polyacrylamide with a higher molecular weight results in lower mechanical degradation. The higher mechanical stability of the sulfonated polymer is attributed to the higher rigidity of its molecules in solution. On the other hand, the ability of the high‐molecular‐weight polymers to form transient, flow‐induced microgels boost their mechanical stability. This ability increases with the increase in the molecular weight of the polymer. Indeed, the microgel solution used in this study demonstrates exceptional mechanical stability. In general, mechanical stability of linear polymers used in chemical enhanced oil recovery can be enhanced by tailoring a polymer that has large side groups similar to the sulfonated polyacrylamide. Also, polyacrylamide‐based microgels can be applied if high mechanical stability is required. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40921.     

Analysis of the foaming mechanisms of materials based on high‐density polyethylene (HDPE) crosslinked with different irradiation doses

Different crosslinked high‐density polyethylene based cellular polymers have been produced by a free foaming process using a chemical blowing agent. The polymer matrix was crosslinked by electron beam irradiation using different doses ranging from 25 to 175 kGy. The main aim of this work is to study the effect of the different irradiation doses on the density, cellular structure, and foaming mechanisms. Results show that irradiation doses as high as 175 kGy have to be used to obtain cellular materials with a low relative density (0.06), cell sizes of around 50 μm, and cell densities of 1.6 × 10⁷ cells cm^?3. The strain hardening of the polymer matrix increases with the irradiation dose leading to an increase of the polymer resistance to be stretched, which helps to avoid undesirable cellular degeneration processes. Irradiation doses lower than 175 kGy are not able to stabilize the cellular structure leading to foams with relative densities higher than 0.1 and degenerated cellular structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46276.     

Synthesis of cassava starch‐g‐poly(methyl methacrylate) copolymers with benzoyl peroxide as an initiator

Graft copolymers of cassava starch and methyl methacrylate (MMA) were synthesized by free‐radical polymerization with benzoyl peroxide (BPO) as an initiator in an aqueous medium at 80°C. The formation of graft copolymers was confirmed by analysis of the obtained products with Fourier transform infrared spectroscopy and scanning electron microscopy. The effects of the amount of cassava starch, the amount of MMA monomer, the amount of BPO, and the reaction time on the grafting characteristics were studied. The optimum condition for grafting were obtained when 5 g of cassava starch, 5 g of MMA, 0.1 g of BPO, and a reaction time of 3 h were used. These condition provided a graft copolymer with 25.00% add‐on, 81.40% monomer conversion, 54.30% homopoly(methyl methacrylate) formed, 45.70% grafting efficiency, 37.20% grafting ratio, and 95.54% yield. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4083–4089, 2006     

Preparation and characterization of poly(L‐lactide) membranes prepared by γ‐radiation‐induced grafting of N‐vinyl pyrrolidone

A copolymer, poly(L ‐lactide)‐g‐poly(N‐vinyl pyrrolidone) (PLLA‐g‐PVP) was prepared with poly(L ‐lactide) (PLLA) and N‐vinyl pyrrolidone in the presence of methanol as a solvent by γ‐ray irradiation. The structure of PLLA‐g‐PVP was characterized by ¹H‐NMR and Fourier transform infrared spectroscopy. The PLLA‐g‐PVP graft ratio calculated by the percentage increase in weight increased with the increase of absorbed dose, and the percentage crystallinity of PLLA‐g‐PVP decreased with increasing graft ratio. The introduction of the poly(N‐vinyl pyrrolidone) chain into PLLA resulted in a decrease in the contact angle of PLLA‐g‐PVP with increasing graft ratio. In vitro degradation testing showed that PLLA‐g‐PVP had a higher degradation rate both in the weight‐loss test and molecular weight measurement because of a lower crystalline percentage and higher hydrophilicity compared to PLLA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Production,cellular structure and thermal conductivity of microcellular (methyl methacrylate)–(butyl acrylate)–(methyl methacrylate) triblock copolymers

Microcellular foaming of a (methyl methacrylate)–(butyl acrylate)–(methyl methacrylate) triblock copolymer was carried out by means of supercritical CO₂ in a single‐step process. The experiments were performed at 40 °C using a pressure of 300 bar (30 MPa) during 24 h. The depressurization times were modified from 2 to 30 min, leading to cell sizes from 10 to 100 µm, and relative densities from 0.11 to 0.17. It was found that the key parameter to control cell size and density was depressurization time: longer depressurization times generated larger cell sizes and lower densities. The thermal conductivity of these materials was measured using the transient plane source technique, and it was found that this decreased as the density was reduced. Various models for the prediction of thermal conductivity by conduction were tested. It was found that all the models underestimated the experimental results due to a significant contribution of radiation heat flow for these materials. Copyright © 2010 Society of Chemical Industry     

Stabilization of CO2‐in‐water emulsions with high internal phase volume using PVAc‐b‐PVP and PVP‐b‐PVAc‐b‐PVP as emulsifying agents

Two newly‐designed hydrocarbon surfactants, that is, poly(vinyl acetate)‐block‐poly(1‐vinyl‐2‐pyrrolidone) (PVAc‐b‐PVP) and PVP‐b‐PVAc‐b‐PVP, were synthesized using reversible addition–fragmentation chain transfer polymerization and used to form CO₂/water (C/W) emulsions with high internal phase volume and good stability against flocculation and coalescence up to 60 h. Their structures were precisely determined by nuclear magnetic resonance, gel permeation chromatography, thermal gravimetric analysis, and differential scanning calorimetry. Besides low temperature and high CO₂ pressure, the surfactant structures were the key factors affecting the formation and stability of high internal phase C/W emulsions, including the polymerization degrees of CO₂‐philic block (PVAc) and hydrophilic block (PVP), as well as the number of hydrophilic tail. The surface tension of the surfactant aqueous solution and the apparent viscosity of the C/W emulsions were also measured to characterize the surfactants efficiency and effectiveness. The surfactants with double hydrophilic tails showed stronger emulsifying ability than those with single hydrophilic tail. The great enhancement of the emulsions stability was due to decrease of the interface tension as well as increase of the steric hindrance in the water lamellae, preventing a frequent collision of CO₂ droplets and their fast coalescence. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46351.     

Preparation of hydrogel impregnated antimicrobial polyurethane foam for absorption of radionuclide contaminated blood and biological fluids

Multi‐purpose polyacrylamide (PAM) and polyacrylamide‐co‐sodiumpolyacrylate (PAM‐co‐NaPA) impregnated polyurethane foams (PUF) loaded with iodine have been prepared by in situ free radical polymerization. The prepared hydrogel networks displayed higher capacity for absorbing biological fluids as compared to regular PUF sheets and cotton matrices used in hospitals for maintaining hygiene conditions in cases of blood spillage and leakages. PAM‐impregnated‐PUF showed 910, 605, and 172% absorption in water, saline, and blood, respectively, whereas PAM‐co‐NaPA‐impregnated‐PUF showed absorption of 1545, 1395, and 269% in water, saline, and blood, respectively in 24 h. Exposure to nuclear, biological, and chemical (NBC) environment has become a grave predicament in today's world necessitating prevention of radiological contaminations especially in medical facilities. PAM‐co‐NaPA‐impregnated‐PUF displayed 97% absorption of Tc⁹⁹ from whole blood whereas PUF sheets were highly hydrophobic and showed only 1% absorption of Tc⁹⁹ from whole blood. It was also demonstrated that modified foams have long‐term broad‐spectrum antimicrobial properties due to sustain release of ionic iodine. Thus, PAM‐co‐NaPA‐impregnated‐PUF sheets have strong potential to be used as matrices for carrying the injured patients, from field conditions to hospitals expose to NBC environment. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43625.     

Preparation and mechanism study of intrinsic hard segment flame-retardant polyurethane foam

The hard segment of polyurethane foam (PUF) plays a special role in degradation and carbonization. In this work, flame-retardant hard segment (HSFR) used to promote fire resistance was synthesized successfully. The limiting oxygen index (LOI), vertical combustion, and micro-combustion calorimetry tests indicated the flame retardancy of the foam was elevated by introducing HSFR. When HSFR with an addition of 60 phr, the LOI value was increased from 17.0 to 25.5%, UL-94 reached V-0 rating, the peak heat release rate (p-HRR) and total heat release (THR) decreased by 63.9% and 10.0%, respectively. In addition, the compressive strength of HSFR-60 increased by five times. Further, the flame-retardant mechanism of HSFR was proposed. In vapor phase, HSFR could generate PO and PO₂, which combine with flammable free radical and hinder segment decomposition. In condensed phase, HSFR could promote the dehydration and carbonization of chain and the formation of dense and graphitized char. This article provides a practical method for the preparation of green, highly effective, and durable flame-retardant PUF.     

Bulk grafting of poly(styrene‐alt‐maleic anhydride) onto preirradiated polyolefin membranes in supercritical carbon dioxide

To take advantage of the property of supercritical carbon dioxide as both a solvent and swelling agent, the bulk grafting of poly(styrene‐alt‐maleic anhydride) [P(MAH‐alt‐St)] onto preirradiated polyolefin membranes was performed by a combination of γ‐ray‐preirradiation‐induced graft copolymerization and supercritical fluid‐swollen polymerization. The trapped radicals on the polyolefin backbones were uniformly distributed by γ‐ray irradiation under a nitrogen atmosphere. Subsequently, these polymeric trapped radicals initiated the alternating copolymerization of styrene (St) and maleic anhydride (MAH) infused into the swollen polymer matrix with the aid of supercritical CO₂. It was important that the graft copolymers were relatively pure without any contaminants, including homopolymers, monomers, and initiators. The experimental results show that the degree of grafting could be easily controlled. In addition, St/MAH could synergistically promote the bulk grafting process and strongly effect on the alternating trend; this was confirmed by element analysis and differential scanning calorimetry. Soxhlet extraction, X‐ray diffraction, and Fourier transform infrared spectroscopy indicated that the P(MAH‐alt‐St) was covalently bonded to the polymeric backbones. Scanning electron microscopy showed that the alternating graft chains were uniformly dispersed throughout the 5‐mm thickness of the polymer membranes on the nanometer scale. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electron beam sterilization of cyclo olefin polymer leads to polymer degradation and production of alkyl radicals

We investigated the effects of electron‐beam (EB) sterilization on syringe barrels manufactured from cyclo olefin polymer (COP). The chemical structure of the polymer was determined by interpreting the ¹³C NMR and DEPT‐135 spectra of the COP resin. The antioxidants in the resin were identified by analyzing the liquid chromatography‐photo diode array‐mass spectrometry (LC‐PDA‐MS) data for the methanol extract of the resin and the gas chromatography‐mass spectrometry (GC‐MS) data for the supercritical methanol degradation products of the extract. NMR and LC‐PDA‐MS analyses revealed that EB sterilization produces degradation products in the COP main chain and reduces the quantity of the antioxidants in the COP resin. ESR spectra of the EB‐sterilized syringe barrels indicated the presence and location of alkyl radicals, which were generated in the COP main chain by EB sterilization. ESR analyses also indicated that the quantity of alkyl radicals decreased over time. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43498.     

Preparation of aluminum hydroxide/aluminum phosphinate flame‐retardant poly(vinyl alcohol) foam through thermal processing

A novel flame‐retardant poly (vinyl alcohol) (PVA) composite foam was prepared successfully through thermal processing, which was filled with high content of flame retardant, based on aluminum hydroxide (ATH) and aluminum phosphinate (AlPi) and using water as plasticizer and blowing agent. The flame‐retardant property and mechanism of the prepared foam matrix were studied by vertical burning test, limiting oxygen index (LOI), cone calorimeter, scanning electronic microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The experimental results showed that the PVA/ATH/AlPi (1/1.2/0.05) composite achieved LOI value of 41% and UL94 V‐0 (3.2 mm) rate. The addition of ATH and AlPi into PVA matrix significantly decreased flammability of the composites, because a more compact and continuous char layer of the PVA/ATH/AlPi composite could be formed, due to the involvement of AlPi in the char‐forming reaction. Compared with the pure PVA sample, the peak heat release rate (PHRR) and total heat release (THR) of PVA/ATH/AlPi (1/1.2/0.05) composite were reduced by 76.5% and 58.2%, respectively. Built upon this PVA‐based foam matrix with good flame retardancy, the flame‐retardant PVA‐based foam was successfully prepared through thermal extrusion. In addition, the influence of water content on melt viscosity, foam structure and mechanical strength was also analyzed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42020.     

Isothermal annealing of poly(lactide‐co‐glycolide) (PLGA) and its effect on radiation degradation

The purpose of this study was to examine how the presence of crystals can retard electron‐beam (e‐beam) radiation degradation, and their effects on the thermal and morphological properties of poly(lactide‐co‐glycolide) (PLGA) upon e‐beam irradiation. Isothermal annealing at 115 °C was carried out on PLGA films and the effect of different annealing times on the degree of crystallinity (DOC) of PLGA was recorded. The DOC increased with annealing time to a maximum value, and remained unchanged with further annealing. The annealed films were then e‐beam irradiated at doses of 5, 10, 20 and 30 Mrad. The degradation of the films was studied by measuring the changes in their molecular weight, DOC, thermal properties and FTIR spectra. It was observed that, regardless of the DOC of the films, the molecular weight of PLGA generally decreased with increasing radiation dose, indicating that chain scission is dominant. However, the extent of degradation is less for the films with a higher DOC. The thermal properties of PLGA also decreased with increasing radiation dose. Radiation increases the DOC for films with initial crystallinity below 5 % but decreases the DOC for films with initial crystallinity above 5 %. Crystals in PLGA films decreased the extent of radiation degradation. Copyright © 2005 Society of Chemical Industry     

Natural rubber/leather waste composite foam: A new eco‐friendly material and recycling approach

This article describes a new approach of recycling the leather waste (shavings) using it as filler in natural rubber foams composites. The foams were prepared using different amounts of leather waste (0–60 parts per hundred of rubber) and submitted to morphological (SEM microscopy) and mechanical analyses (cyclic stress–strain compression). The increase of leather shavings on the composite causes an increase of viscosity in the mixture, which reflects in the foaming process. This results in smaller and fairly uniform cells. Furthermore, expanded rubber has the biggest cell size, with more than 70% of cell with 1000 µm, while the composite with the higher concentration of leather has around 80% of total number of cells with 100–400 µm. The mechanical parameters were found to depend on the leather dust concentration. Moreover, the stiffness rises with the increase of leather shavings; consequently, the compression force for expanded rubber was 0.126 MPa as well as the composite with higher concentration of leather was 7.55 MPa. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41636.