Flame‐retardant and thermal degradation mechanism of low‐density polyethylene modified with aluminum hypophosphite and microencapsulated red phosphorus

Aluminum hypophosphite (AHP), a novel flame retardant, was used to improve the flame retardancy of low‐density polyethylene (LDPE) with microencapsulated red phosphorus (MRP). The synergistic effect between MRP and AHP was investigated by the limiting oxygen index (LOI), vertical burning test (UL‐94), and thermogravimetric analysis. When the contents of MRP and AHP were 10 and 30 phr, the LOI of LDPE/10MRP/30AHP composite was 25.5%, and it passed the UL‐94 V‐0 rating (the number before “MRP” and “AHP” is the loading of MRP and AHP, In LDPE/10MRP/30AHP, the content of the LDPE, MRP and AHP is 100phr, 10phr and 30phr, where phr refers to parts per hundreds of resin). The results of cone calorimetry testing show that the heat release rate of the composites was significantly reduced, and the strength of the char layer improved when the loading of AHP increased. The thermal stability of the LDPE/10MRP/30AHP composite was enhanced. The structure of the char was investigated by Fourier transform infrared spectrometry and scanning electron microscopy/energy‐dispersive spectrometry. The results indicate that AHP promoted the formation of stable char. This research provided a good way to prepare flame‐retardant materials with a halogen‐free flame retardant and contributed to environmental protection. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43225.     

Study of using aluminum hypophosphite as a flame retardant for low‐density polyethylene

Aluminum hypophosphite (AHP) was first used to improve the flame retardance of low‐density polyethylene (LDPE). The flame‐retardant properties of LDPE composites were investigated by the limiting oxygen index, vertical burning test (UL‐94), microscale combustion calorimetry, and cone calorimeter tests. The results showed that the incorporation of AHP could improve the flame retardancy of LDPE dramatically, the limiting oxygen index of LDPE containing 50 phr AHP reached 27.5%, and the UL‐94 could pass V‐0 rating. The cone calorimeter test results indicated that PP/AHP composite exhibited superior performance, and the heat release rate and the total heat release of composites were significantly reduced. In addition, the strength of the char was improved with the load of AHP increased. The structure of the char was researched by Fourier transform infrared spectrometry (FTIR) and scanning electron microscope‐energy dispersive spectrometer, and the results revealed that AHP promoted the formation of compact char layer. The TG‐FTIR analyses proved that AHP could react with LDPE to reduce the production of olefin in gas phase. Moreover, the structure of P–O–C was found, and the effective mechanism of AHP in LDPE composites was also hypothesized in this work.     

Effect of carbon black structure on low‐strain conductivity of polypropylene and low‐density polyethylene composites

The influences of carbon black (CB) structure on the percolation threshold, mechanical properties, and strain‐resistivity response of polymer composites are studied. Low‐density polyethylene (LDPE) and polypropylene (PP) samples were blended with five different types of CB differing in structure. Relatively low strains were studied; the maximum strain was 10%. It was found that the CB concentration for maximum strain‐sensitivity of the electrical conductivity is higher for low structure carbon blacks but is essentially independent of the CB structure for medium‐ to high‐structure carbon blacks. However, the composite containing the largest particle size carbon black clearly showed the highest strain‐sensitivity to electrical conduction. The mechanical properties and sensitivity of electrical resistivity to tensile strain of the filled composites examined in the study are also presented and discussed. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Effect of various alumina nano‐fillers on the thermal and mechanical behaviour of low‐density polyethylene–Al2O3 composites

Two different alumina powders were dispersed in low‐density polyethylene (LDPE) to evaluate if any role can be ascribed to the crystalline phase, size and morphology of the alumina filler. In particular a submicrometric α‐alumina and a nanocrystalline transition (γ/δ) alumina were added to the polymer at 5 wt% concentration, using a Brabender mixing unit. Both the neat inorganic fillers showed a good dispersibility in the polyolefin. The thermal and mechanical properties of the composites obtained were evaluated. As expected, a significant increase of the stiffness and abrasion resistance of LDPE was achieved in both cases. Furthermore, the composites showed a higher thermo‐oxidative stability with respect to neat LDPE. Independent of their crystalline phase, size and morphology, both fillers gave a similar enhancement of composite features. Copyright © 2010 Society of Chemical Industry     

Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150°C and shear rate of 16.4 to 5470 s^?1 were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 432–442, 2003     

Influence of radiation structures on positive‐temperature‐coefficient and negative‐temperature‐coefficient effects of irradiated low‐density polyethylene/carbon black composites

The electrical‐resistivity/temperature behaviors of low‐density polyethylene (LDPE)/carbon black (CB) composites irradiated with ⁶⁰Co γ rays were studied. The experimental results showed that the irradiated composites could be separated into insoluble crosslinking networks with CB (gel) and soluble components (sol) by solvent‐extraction techniques. When the sol of an irradiated LDPE/CB composite was extracted, the electrical conductivity of the system increased. The positive‐temperature‐coefficient (PTC) and negative‐temperature‐coefficient (NTC) intensities of the gels of the irradiated composites became extremely small and independent of the radiation dose. The sols and gels of the irradiated LDPE/CB composites, which had different thermal behaviors, played important roles in the appearances of the PTC and NTC effects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 700–704, 2005     

Submicron copper‐low‐density polyethylene conducting composites: Structural,electrical, and percolation threshold

Copper‐embedded low‐density polyethylene (LDPE) composites were fabricated using different copper concentrations in the polymer matrix. The copper particles were spherical with a mean particle size between 200 and 300 nm. All the samples were compacted under pressure and melted. The LDPE matrix was analyzed using gel permeation chromatography (GPC) and it did not evidence degradation of the LDPE matrix. The microstructure of the composites was examined with scanning electron microscopy. The electrical conductivity was measured as a function of the copper content, and the composite fabricated with a 10 vol % copper presented a conductivity 15 orders of magnitude higher than that of pure LDPE. The enhancement in conductivity can be explained by means of segregated percolation path theory and the experimental results are in agreement with the theoretical law. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Biodegradable supramolecular composites of poly(ε‐caprolactone) and low‐molecular‐weight organic gelators

When a homogeneous hot liquid of poly(ε‐caprolactone) (PCL) with (R)‐12‐hydroxystearic acid (HSA) or N‐carbobenzyloxy‐L ‐isoleucylaminooctadecane (CIA) was gradually cooled to room temperature, the mixture became gelatinous material and then solidified to give a PCL/HSA or PCL/CIA composite. The rheological measurements of the mixtures of PCL with HSA and CIA revealed that the organogels are formed at around 70–50°C and 100–73°C during the cooling process, respectively. Furthermore, the formation of supramolecular fibrillar networks was confirmed by the microscopic and differential scanning calorimetric analyses. The tensile moduli of both the composites were improved by the addition of CIA and HSA. Both the composites showed so high biodegradability as PCL. The fibrillar networks of the composites were also regenerated during the repeated cooling process from the isotropic liquid. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Recycled milk pouch and virgin low‐density polyethylene/linear low‐density polyethylene based coir fiber composites

The viability of the thermomechanical recycling of postconsumer milk pouches [a 50 : 50 low‐density polyethylene/linear low‐density polyethylene (LDPE–LLDPE) blend] and their use as polymeric matrices for coir‐fiber‐reinforced composites were investigated. The mechanical, thermal, morphological, and water absorption properties of recycled milk pouch polymer/coir fiber composites with different treated and untreated fiber contents were evaluated and compared with those of virgin LDPE–LLDPE/coir fiber composites. The water absorption of the composites measured at three different temperatures (25, 45, and 75°C) was found to follow Fickian diffusion. The mechanical properties of the composites significantly deteriorated after water absorption. The recycled polymer/coir fiber composites showed inferior mechanical performances and thermooxidative stability (oxidation induction time and oxidation temperature) in comparison with those observed for virgin polymer/fiber composites. However, a small quantity of a coupling agent (2 wt %) significantly improved all the mechanical, thermal, and moisture‐resistance properties of both types of composites. The overall mechanical performances of the composites containing recycled and virgin polymer matrices were correlated by the phase morphology, as observed with scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Photofabrication of biofiber‐based polymer matrix composites

The novel development of a photofabrication process of biofiber composites, based on oil palm empty fruit bunch fibers, is reported. The process consists of the following steps: (1) the preparation by a wet process of nonwoven mat of biofiber, either alone or in combination with glass and nylon; (2) drying the mat; (3) preparation of photocurable resin matrix, consisting of vinyl ester and photoinitiator; (4) impregnation of the mat by photocurable resin; and (5) irradiation of the impregnated mat by UV radiation to effect the cure of the composite. The nonwoven mat was formed in a “headbox” into which was poured a slurry of fibers. A wet mat was formed by after dewatering of the slurry. Biofiber, glass, and nylon fibers were mixed in different proportions. A “mixture experimental design” was used to generate experimental compositions of the reinforcing fibers and to model dependency of the response variables on the components through mathematical relationships. These relationships were meant to (1) determine the effect of composition of the reinforcing fibers on the physical and mechanical properties, (2) predict the response for any unknown composition of fibers, and (3) determine the optimum values of any identified properties. Because the product was characterized by multiple responses, simultaneous maximization of all properties was not feasible. The product must be considered in the definition of the trade‐off or compromise of properties to obtain overall satisfactory performance. Such an optimization was carried out and the results are reported. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1493–1499, 2005     

Glass‐polymer melt hybrids. I: Viscoelastic properties of novel affordable organic‐inorganic polymer hybrids

A novel class of organic‐inorganic polymer hybrids was developed by melt‐blending up to 50 (v/v) % [about 83 (w/w) %] tin‐based polyphosphate glass (Pglass) and low‐density polyethylene (LDPE) in conventional plastics processing equipment. The liquid‐ and solid‐state rheology of the polymer hybrids was studied under oscillatory shear flow and deformation to understand the behavior of these materials and to accelerate efforts to melt process the Pglass with organic polymers. All the materials were found to be linearly viscoelastic in the range of temperature and frequencies examined and their viscoelastic functions increased with increasing Pglass concentration. The Pglass significantly enhanced the shear‐thinning characteristics of the Pglass‐LDPE hybrid, indicating the presence of nonlinear chemical and physical interactions between the hybrid components. Morphological examination of the materials by scanning electron microscopy revealed interesting evolution of microstructure of the Pglass phase from droplets (or round beads) to elongated and interpenetrating network structures as the glass concentration was increased in the Pglass‐LDPE hybrids. Melt viscosities of the materials were well described by a simple power‐law equation and a Maxwellian (Hookean) model with three relaxation times. Time‐temperature superpositioning (TTS) of the complex viscosity versus frequency data was excellent at 170°C < T < 220°C and the temperature dependencies of the shift factors conformed excellently well to predictions from an Arrhenius‐type relation, enabling calculation of the flow‐activation energies (25–285 kj/mol) for the materials. The beneficial function of the Pglass in the hybrid system was significantly enhanced by pre‐treating the glass with coupling agents prior to incorporating them into the Pglass‐LDPE hybrids.     

Study on short glass fiber‐reinforced poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) composites

Biobased non‐fossil polyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 4.0 mol % 4‐hydroxybutyrate (4HB) was melt‐mixed with short glass fibers (SGF) via a co‐rotating twin‐screw extruder. The compositing conditions, average glass fiber length and distribution, thermal, crystallization, and mechanical properties of the P3/4HB/SGF composites were investigated. Calcium stearate, two kinds of paraffin wax and modified ethylene bis‐stearamide (TAF) were investigated as lubricants for the P3/4HB/SGF composites. It revealed that TAF is the most efficient lubricant of the P3/4HB/SGF composites. Coupling agents 2,2′‐(1,3‐phenylene)bis‐2‐oxazoline (1,3‐PBO) and pyromellitic dianhydride (PMDA) were used as end‐group crosslinkers to reduce the degradation of P3/4HB and increase the mechanical properties of the P3/4HB/SGF composites. It showed that 1,3‐PBO is the efficient coupling agent. The optimum condition of the P3/4HB/SGF composites is 1.5 phr TAF, 1.0 phr 1,3‐PBO, and 30 wt % glass fiber content. And the maximum of tensile strength, tensile modulus, and impact strength of the composites is 3.7, 6.6, 1.8 times of the neat P3/4HB polymer, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological,thermal, and morphological properties of low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene and linear low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene blends

The dynamic rheological behavior of low‐density polyethylene (LDPE)/ultra‐high‐molecular‐weight polyethylene (UHMWPE) blends and linear low‐density polyethylene (LLDPE)/UHMWPE blends was measured in a parallel‐plate rheometer at 180, 190, and 200°C. Analysis of the log–additivity rule, Cole–Cole plots, Han curves, and Van Gurp curves of the LDPE/UHMWPE blends indicated that the blends were miscible in the melt. In contrast, the rheological properties of LLDPE/UHMWPE showed that the miscibility of the blends was decided by the composition of LLDPE. The differential scanning calorimetry results and scanning electron microscopy photos of the LLDPE/UHMWPE blends were consistent with the rheological properties, whereas with regard to the thermal and morphological properties of LDPE/UHMWPE blends, the results reveal three endothermic peaks and phase separation, which indicated a liquid–solid phase separation in the LDPE/UHMWPE blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of sodium hydroxide treatment on the properties of low‐density polyethylene composites filled with chicken feather fiber

The effects of alkali treatment with sodium hydroxide on the tensile properties, morphology, thermal degradation, and mass swell of low‐density polyethylene (LDPE)/(chicken feather fibers (CFF)) composites were studied. The LDPE/CFF composites were prepared by using a Z‐Blade mixer at 180^oC and a rotor speed of 50 rpm. The LDPE/CFF‐_Treated composites exhibited higher tensile strength, Young's modulus, and final decomposition temperature but had lower mass swell percentage and elongation at break than the LDPE/CFF composites. An SEM morphology study showed that the CFF treatment could significantly improve adhesion at the interface and lead to ingress of the fiber into the LDPE phase. Thermogravimetric analysis indicated that the LDPE/CFF‐_Treated composites had higher thermal stability than the LDPE/CFF composites. J. VINYL ADDIT. TECHNOL., 20:36–41, 2014. © 2014 Society of Plastics Engineers     

Effects of ultrasonic oscillations on processing behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene/low‐density polyethylene blends

The influences of ultrasonic oscillations on rheological behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene (mLLDPE)/low‐density polyethylene (LDPE) blends were investigated. The experimental results showed that the presence of ultrasonic oscillations can increase the extrusion productivity of mLLDPE/LDPE blends and decrease their die pressure and melt viscosity during extrusion. Incorporation of LDPE increases the critical shear rate for sharkskin formation of extrudate, crystallinity, and mechanical properties of mLLDPE. The processing behavior and mechanical properties of mLLDPE/LDPE blends were further improved in the presence of ultrasonic oscillations during extrusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2522–2527, 2004     

In situ reactive compatibilization and reinforcement of peroxide dynamically vulcanized polypropylene/ethylene‐propylene‐diene monomer tpv by zinc dimethacrylate

This work demonstrates an approach of in situ reactive compatibilization between polypropylene (PP) and ethylene‐propylene‐diene monomer (EPDM) by using ZDMA as a compatibilizer and, simultaneously, as a very strong reinforcing agent. With 7phr ZDMA in the PP/EPDM (30/70, w/w) thermoplastic vulcanizate (TPV), the tensile strength and elongation at break were increased from 5.3 MPa and 222% up to 11.2 MPa and 396%, respectively. Increasing the PP concentration further improved mechanical properties of the TPVs with ZDMA. This tremendous reinforcing as well as the compatibilization effect of the ZDMA was understood by polymerization of ZDMA and ZDMA reacting with EPDM and PP during peroxide induced dynamic vulcanization. A peculiar nano‐composite structure that the crosslinked rubber particles were “bonded” by a transition zone which containing numerous of nano‐particles with dimensions of about 20–30 nm was observed from transmission electron microscopy (TEM). Scanning electron microscopy (SEM) results showed that increase of PP/EPDM ratio reduced the size of crosslinked EPDM particles. Moreover, we found that the ZDMA reinforced EPDM particles resulted in a higher tan δ peak temperature for EPDM phase and built “filler‐filler”‐like networking in the PP melt. POLYM. COMPOS. 34:1357–1366, 2013. © 2013 Society of Plastics Engineers     

Photodegradation of some low‐density polyethylene–montmorillonite nanocomposites containing an oligomeric compatibilizer

The photo‐oxidation behavior at the exposed surfaces of maleated low‐density polyethylene [LDPE poly(ethylene‐co‐butylacrylate‐co‐maleic anhydride) (PEBAMA)] and montmorillonite (MMT) composites was studied using attenuated total reflection Fourier transform infrared spectroscopy, X‐ray diffraction (XRD), transmission electron microscopy (TEM), and mechanical testing. Two different MMT clays were used with the maleated polyethylene, an unmodified clay, MMT, and an organically modified montmorillonite (OMMT) clay which was significantly exfoliated in the composite. The morphologies of sample films were examined by XRD and TEM. The results were explained in terms of the effect of the compatibilizing agent PEBAMA on the clay dispersion. It was found that the OMMT particles were exfoliated in the polymer matrix in the presence of the PEBAMA, whereas the MMT clay particles were agglomerated in this matrix. Both mechanical and spectroscopic analyses showed that the rates of photo oxidative degradation of the LDPE‐PEBAMA–OMMT were higher than those for LDPE and LDPE‐PEBAMA–MMT. The acceleration of the photo‐oxidative degradation for LDPE‐PEBAMA–OMMT is attributed to the effects of the compatibilizer and the organic modifier in the composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40788.     

Die–swell behavior of glass bead‐filled low‐density polyethylene composite melts at high extrusion rates

The extrudate swell behavior of glass bead‐filled low‐density polyethylene (LDPE) composite melts was investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 140 to 170°C. The results show that the die swell ratio (B) of the melts increases nonlinearly with increasing apparent shear rates for the system filled with the surface of glass beads pretreated with a silane coupling agent, while the B for the system filled with uncoated particles remains almost constant when the true wall shear rate is greater than 2000 s⁻¹ at a constant temperature. The values of B for both the pure LDPE and the filled systems decreases linearly with an increase of the temperature and an increase of the die diameter at fixed shear rates, and the sensitivity of B on the die diameter and temperature for the former is higher than that of the latter. Furthermore, the effect of the filler content on B is insignificant, while the values of B decreases, obviously, with an increasing glass bead diameter (d) when d is smaller than 50 μm; then B varies slightly with d. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 419–424, 2000     

Recycling of poly(ethylene terephthalate) as polymer‐polymer composites

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.     

Crystallization behavior of glass bead‐filled low‐density polyethylene composites

The effects of the filler content and the filler size on the crystallization and melting behavior of glass bead‐filled low‐density polyethylene (LDPE) composites have been studied by means of a differential scanning calorimeter (DSC). It is found that the values of melting enthalpy (ΔH_c) and degree of crystallinity (x_c) of the composites increase nonlinearly with increasing the volume fraction of glass beads, ϕ_f, when ϕ_f is greater than 5%; the crystallization temperatures (T_c) and the melting temperatures (T_m) of the composites are slightly higher than those of the pure LDPE; the effects of glass bead size on x_c, T_c, and T_m are insignificant at lower filler content; but the x_c for the LDPE filled with smaller glass beads is obviously greater than that of the filled system with bigger ones at higher ϕ_f. It suggests that small particles are more beneficial to increase in crystallinity of the composites than big ones, especially at higher filler content. In addition, the influence of the filler surface pretreated with a silane coupling agent on the crystallization behavior are not too outstanding at lower inclusion concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 687–692, 1999