Phase change materials based on low-density polyethylene/paraffin wax blends

Phase change materials, based on low-density polyethylene blended with soft and hard paraffin waxes respectively, were studied in this paper. DSC, DMA, TGA and SEM were employed to determine the structure and properties of the blends. The blends were able to absorb large amounts of heat energy due to melting of paraffin wax, whereas the LDPE matrix kept the material in a compact shape on macroscopic level. The hard paraffin wax was, however, much more miscible with LDPE because of co-crystallization than the soft paraffin wax. LDPE blended with hard paraffin wax degrades in just one step, while blends containing soft paraffin wax degrade in two distinguishable steps. SEM showed completely different morphology for the two paraffin waxes and confirmed the lower miscibility of LDPE and soft paraffin wax. DMA analyses demonstrated the toughening effect of the waxes on the polymer matrix. This technique was also used to follow the thermal expansion as well as the dimensional stability of the samples during thermal cycling. The most visible expansion could be seen in the first cycle, probably due to a totally different thermal history of the sample. With further cycling the dimensions stabilized after two and four cycles for soft and hard paraffin wax, respectively. Controlled force ramp testing on DMA confirmed poor material strength of the blends containing soft wax, especially at temperatures above wax melting.     

Compatibility effect on the thermal degradation behaviour of polypropylene blends with polyamide 6, ethylene propylene diene copolymer and polyurethane

The morphology and thermal behaviour of polypropylene/polyamide 6 (PP/PA6), polypropylene/copolymer ethylene propylene diene (PP/PEBAX) and polypropylene/rigid polyurethane (PP/PUR) blends compatibilised with polypropylene-graft-maleic anhydride (PP-g-MA) were studied using scanning electron microscopy and thermogravimetric analyses. The study focuses on the influence of different blends obtained by mixing a thermoplastic, thermoplastic elastomer or thermoset with PP, compatibilised with PP-g-MA. The compatibilising effect of PP-g-MA in an immiscible PP/PA6 blend induces a homogeneous dispersion due to interfacial adhesion. For the PP/PEBAX and PP/PUR binary blends studied slight changes in the morphology were observed with a continuous phase but the PEBAX or PUR domains remained in the PP matrix. The deconvolution of the TGA curve permitted an evaluation of the decomposition stage of the undiluted and blend systems. Thermal stability is slightly influenced by the position of the maximum decomposition rate temperature of the first derivative thermogravimetric curve (DTG). However, the DTG curve profile remains consistent. The activation energy of undiluted PP was in the range of 162–169 kJ mol⁻¹ determined by the Ozawa method. The stabilized activation energy value for all blends studied above a 0.4 weight-loss fraction is discussed.     

Modification of Interfacial Interaction of PBT/PP Blends by Adding Main-chain Liquid Crystalline Ionomer with Sulfonic Group

A main-chain liquid crystalline ionomer(MLCI)containing sulfonic group was synthesized by an interfacial condensation reaction.The MLCI was blended with polybutylene terephthalate(PBT)and polypropylene...     

Thermal and structural studies of polypropylene blended with esterified industrial waste lignin

Microwave-assisted chemical modification of lignin was achieved through esterification using maleic anhydride. Modified lignin (ML) was blended in different proportions up to 25 mass% with polypropylene (PP) using Brabender electronic Plasticorder at 190 °C. The structural and thermal properties of blends were investigated by thermogravometric analysis (TG), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). TG analysis showed increased thermal stability of blends due to antioxidant property of ML, which opposed oxidative degradation of PP. DSC analysis indicted slight depression in a glass transition temperature and melting temperature of blends due to partial miscible blend behavior between PP and ML. All blends showed higher crystallization temperatures and continuously reducing percentage crystallinity with increasing ML proportion in the blends. WAXD analysis indicated that PP crystallized in β polymeric form in addition to α-form in the presence of ML. However, proportion of β-form did not show linear relation with increase in ML proportion, thus ML acts as β nucleating agent in the PP matrix. SEM analysis showed good dispersion/miscibility in PP matrix indicating modification in lignin is useful.     

Phase morphology development in PP/PA6 blends induced by a maleated thermoplastic elastomer

The effects of maleated thermoplastic elastomer (TPEg) on morphological development of polypropylene (PP)/polyamide 6 (PA6) blends with a fixed PA6 content (30 wt %) were investigated. For purpose of comparison, nonmaleated thermoplastic elastomer (TPE) was also added to the above binary blends. A comparative study of FTIR spectroscopy in above both ternary blends confirmed the formation of in situ graft copolymer in the PP/PA6/TPEg blend. Dynamic mechanical analysis (DMA) indicated that un‐like TPE, the incorporation of TPEg remarkably affected both intensity and position of loss peaks of blend components. Scanning electron microscopy (SEM) demonstrated that PP/PA6/TPE blends still exhibited poor interfacial adhesion between the dispersed phase and matrix. However, the use of TPEg induced a finer dispersion and promoted interfacial adhesion. Transmission electron microscopy (TEM) for PP/PA6/TPEg blends showed that a core‐shell structure consisting of PA6 particles encapsulated by an interlayer was formed in PP matrix. With the concentration of TPEg increasing, the dispersed core‐shell particles morphology was found to transform from discrete acorn‐type particles to agglomerate with increasing degree of encapsulation. The modified Harkin's equation was applied to illustrate the evolution of morphology with TPEg concentration. “Droplet‐sandwiched experiments” further confirmed the encapsulation morphology in PP/PA6/TPEg blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1050–1061, 2006     

Thermal behaviour of compatibilised polypropylene nanocomposite: Effect of processing conditions

The thermal properties and fire behaviour of polypropylene (PP) nanocomposites were investigated using differential scanning calorimetry, dynamic-mechanical analysis, thermogravimetric analysis and glow wire test. In order to study the morphological structure of the materials obtained, TEM and XRD analyses were also carried out. The nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. Particular attention was given to studying the influence of different processing conditions (barrel temperature profile and screw rate) and compositions of PP-nanoclay blends (clay content, use of compatibiliser) on the thermal properties of the nanocomposites.The results show that all the properties analysed were strongly influenced by the nanocomposite composition; instead, the processing conditions greatly affect only the dynamic-mechanical properties. DSC curves show that the crystallinity is deeply influenced by the presence of the clay in the matrix, owing to the fact that the filler acts as nucleating agent. DMA curves show that materials processed at low temperature profile and high shear stress, i.e. when a good clay dispersion is achieved, are characterised by an enhanced modulus, thus indicating that the incorporation of clay into the PP matrix remarkably enhances its stiffness and has good reinforcing effects. TGA traces in oxidizing atmosphere show a drastic shift of the weight loss curve towards higher temperature and no variation of the onset temperature (i.e. the temperature at which degradation begins). The TGA analyses in inert atmosphere show instead marked increase of this parameter (about 200 °C) and no shift of weight loss curves. Glow wire results highlight that polymer nanocomposites are characterised by enhanced fire behaviour.     

Morphology and Properties of PP In-reactor Alloys Prepared with a MgCl2/TiCl4/Diisobutyl Phthalate/Phosphate Tris-methylphenyl Ester Catalyst System

A series of polypropylene(PP)/poly(ethylene-co-propylene) in-reactor alloys with different ethylene contents was prepared through a two-stage polymerization process using a MgCl₂/TiCl₄/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system. The ethylene content, particle shape, fractured surface, and glass-transition temperature(T_g) of the obtained PP in-reactor alloys were characterized by means of nuclear magnetic resonance, scanning electron microscopy(SEM), and dynamic mechanical analysis(DMA). The ethylene content of the PP alloys increased from 2.34% to 26.69% when the propylene/ethylene feed ratio was increased from 66/34 to 54/46(molar ratio). Morevoer, the increment in ethylene content increased the notched Izod impact strength of the resulting PP alloys. The impact strength of the PP alloy with an ethylene content of 26.69% was 55.8 kJ/m², which is 12.7 times that of isotactic polypropylene. The results of DMA and SEM analysis reveal that ethylene-propylene random copolymer(EPR) in the PP alloy has a low T_g of ca. -50 ℃ and a high interface compatibility with the PP matrix. The excellent impact performance of the PP alloy can be attributed to the uniform dispersal of EPR in the alloy particles and PP matrix.     

In situ reactive compatibilization of polypropylene/epoxidized natural rubber blends by electron induced reactive processing: novel in‐line mixing technology

Blends of polypropylene (PP) and epoxidized natural rubber (ENR) were prepared by an in‐line electron induced reactive processing technique. The mixing was done in a Brabender mixing chamber coupled with an electron accelerator. The effect of sequence of electron treatment on the compatibilization of non‐polar PP and polar ENR was investigated in the presence of triallyl cyanurate (TAC). Finally, the resulting blends were characterized by different techniques, namely, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), tensile tests, and rheological studies. Generation of phase coupling and chemical compatibilization were observed from FTIR analysis. DMA studies showed enhanced high‐temperature modulus (above the glass transition temperature of both components) followed up by lowering in the tan δ peak. Rheological studies showed increase in modulus at low frequencies. Electron treatment and incorporation of rubber phase into PP showed significant effect on the degree of crystallinity of the blends, which was characterized by DSC study. The results obtained from FTIR, DMA, SEM, rheological studies, and tensile tests strongly affirmed that electron induced reactive processing of PP in presence of TAC before adding of ENR performed the best amongst all samples modified with electrons investigated in this study. Copyright © 2010 John Wiley & Sons, Ltd.     

FIBRE-FORMING OF ETHYL CELLULOSE IN POLYPROPYLENE MELT

Ethyl cellulose (EC), taken as a thermotropic liquid crystalline polymer, was blended with polypropylene (PP), followed by injection molding. Fibre-forming of EC in the PP matrix is analyzed,based on the rheological data,dynamic mechanical analysis and fracture micrographs of EC/PP blends. The addition of maleated PP, for the modification of the interphasial interaction between the PP matrix and the EC fibrils, did not impair the fiber formation substantially.     

Barrier Dispersion-Based Coatings Containing Natural and Paraffin Waxes

Petroleum, synthetic, and natural waxes have been used as hydrophobic bases for dispersions intended for use as barrier coatings for packaging paper. Oil-in-water dispersions with alkaline pH were prepared by a two-step homogenization procedure containing paraffin wax, with various characteristics, the Fischer–Tropsch synthesis product or beeswax. The size of the dispersed particles determined by dynamic light scattering depended on the type of hydrophobic base used and was in the range of 350–440 nm. The ability of dispersion particles in aggregation driven by electrostatic attraction, evaluated by Zeta potential analysis by electrophoretic light scattering, was from −26 to −50 mV. Static multiply light scattering was used for 30 days of stability assessment and helped to select the dispersion with a Sarawax SX70 wax base as the most stable. Dispersions were further used for coating the backing of kraft paper by the Meyer rod method. Coated paper with an applied coating of 6 g/m² had very good hydrophobic properties (Cobb60 < 4 g/m²), sufficient strength properties, and air permeation, which enabled its application as a packaging material. The dispersions based on Sarawax SX70 wax were evaluated as the best coating for Mondi ProVantage Kraftliner 125 g/m² backing paper. Good hydrophobic properties and strength properties indicate the possibility of using the SX70-based wax dispersion coating as a replacement for PFAS coatings in some applications.     

Natural aging of shape stabilized phase change materials based on paraffin wax

Natural aging of shape-stabilized phase change materials containing linear low density polyethylene (LLDPE), paraffin wax and expanded graphite (EG) in Qatari climate has been studied. It was found that expanded graphite significantly improved the performance of prepared SSPCMs in multiple ways. Firstly, EG suppressed leakage of paraffin wax from the compact shape of SSPCMs. The addition of 15 wt% of EG to shape stabilized phase change materials (SSPCMs) containing 50 wt% of wax caused a decreasing in the leakage of wax by 50% over 210 days of natural aging.Secondly, ∖expanded graphite enhanced the photochemical stability of the blends; this was confirmed by FTIR analysis, where carbonyl index decreased with EG content.     

Photopolymerization and toughening performance in polypropylene of hyperbranched polyurethane acrylate

A novel UV-curable hyperbranched polyurethane acrylate (HUA) was synthesized and found to polymerize rapidly in the presence of 5 wt.% benzophenone in N₂ under UV exposure. The photopolymerization kinetics of HUA was studied by differential photocalorimetry (DPC). Its toughening effect for polypropylene (PP) was investigated by tensile and impact tests of the UV irradiated PP/HUA blends. The morphological structures and thermal behavior were determined by polarized optical microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The obtained results demonstrate that (1) the maximum photopolymerization rate increases with raising temperature up to 140 °C, whereas decreases at above 150 °C. The activation energy of 19 kJ mol⁻¹ for the photopolymerization was obtained at below 140 °C from the Arrhenius plot, while it is negative at above 150 °C. (2) The incorporation of 5 wt.% HUA greatly improved the notched impact strength of PP matrix with a slight improvement in the tensile strength and without obvious decline in breaking elongation. These results correlate well with SEM observation. (3) During the UV irradiation of PP/HUA blends, PP can be crosslinked/grafted with the cured HUA particles, resulting in the increase of the impact strength of PP matrix. (4) The cured HUA particles in the PP/HUA blends act as heterogeneous nucleation agent for PP, which results in the decrease of spherulite size and less perfection of PP crystals.     

Synergistic effects of aluminum hypophosphite on intumescent flame retardant polypropylene system

The effects of aluminum hypophosphite(AHP) as a synergistic agent on the flame retardancy and thermal degradation behavior of intumescent flame retardant polypropylene composites(PP/IFR) containing ammonium polyphosphate(APP) and triazine charring-foaming agent(CFA) were investigated by limiting oxygen index(LOI), UL-94 measurement, thermogravimetric analysis(TGA), cone calorimeter test(CONE), scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). It was found that the combination of IFR with AHP exhibited an evident synergistic effect and enhanced the flame retardant efficiency for PP matrix. The specimens with the thickness of 0.8 mm can pass UL-94 V-0 rating and the LOI value reaches 33.5% based on the total loading of flame retardant of 24 wt%, and the optimum mass fraction of AHP/IFR is 1:6. The TGA data revealed that AHP could change the degradation behavior of IFR and PP/IFR system, enhance the thermal stability of the IFR and PP/IFR systems at high temperatures and promote the char residue formation. The CONE results revealed that IFR/AHP blends can efficiently reduce the combustion parameters of PP, such as heat release rate(HRR), total heat release(THR), smoke production rate(SPR) and so on. The morphological structures of char residue demonstrated that AHP is of benefit to the formation of a more compact and homogeneous char layer on the materials surface during burning. The analysis of XPS indicates that AHP may promote the formation of sufficient char on the materials surface and improve the flame retardant properties.     

Morphology,mechanical and thermal properties of composites of polypropylene and nanostructured wollastonite filler

Nanostructured wollastonite was synthesized by a sol–gel method and then used as a filler for polypropylene (PP). The obtained wollastonite particles were investigated using XRD, TEM and FTIR techniques. Non-isothermal crystallization measurements revealed that the wollastonite filler reduced the crystallization temperature of the matrix. TGA analyses showed improved thermal stability of the nanocomposite with respect to that of the pure polypropylene. From the DMA tan δ curves, it was concluded that the introduction of the filler into the PP matrix induced a slight shift of the β-transition (glass transition) towards higher temperature. The measurements of storage moduli showed that the nanocomposites have higher stiffness than the pure PP over the whole range of test temperature. An increase in stiffness was also confirmed by tensile measurements.     

Flame retardant polypropylene through the joint action of sepiolite and polyamide 6

The influence of the incorporation of polyamide-6 (PA) and natural sepiolite nanoparticles on both the thermal degradation and fire behaviour of polypropylene (PP) matrix has been investigated by thermogravimetric analysis (TGA) and mass loss calorimetry. For that purpose, PP/PA blends and nanocomposites thereof were prepared by melt processing. TGA results evidenced that the use of maleic anhydride grafted-polypropylene (MA-g-PP) as compatibilizer led to a significant improvement in thermal stability under air. Such improvement was linked to the formation of a char layer preventing the thermo-oxidative degradation of PP. Interestingly, the thermal resistance of this char layer was further improved by adding 5 wt% of natural sepiolite leading to important increase of time to ignition and reduction of peak of heat release rate (pHRR) during mass loss calorimeter test.     

Nonisothermal crystallization behavior of isotactic polypropylene/ thermoplastic rubber blends

The morphology and crystallization behavior of blends of polypropylene (PP) and an ethylene-based thermoplastic elastomer (TPO) were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The SEM images showed a two-phase morphology for these blends. As TPO was partially crystalline, two distinct peaks were observed in both heating and cooling scans of DSC. The crystallization temperature of TPO in blends was higher than pure TPO. In contrast, the crystallization temperature of PP in blends was lower than pure PP. The crystallization behavior of blends was modeled by Avrami equation. It was observed that the presence of TPO accelerated the growth rate of crystals of PP in PP/TPO blends.     

多组份聚丙烯共混物的微观结构及共混纤维的染色性能

研究了PP GPET、PP GPET EVA、PP GPET EVA PS共混物的结构和性能 .研究表明 ,PP GPET体系属于非相容共混体系 ,共混物呈典型海岛型两相结构 ,EVA的加入可以改善体系相容性 ;共混物的结晶度比纯聚丙烯低 ,PS有增大共混物晶粒尺寸的作用 ;改性聚丙烯纤维的染色性有明显提高 ,用分散染料E EX可染成深蓝色     

Crystalline structure of polypropylene in blends with thermoplastic elastomers after electron beam irradiation

Isotactic polypropylene (PP) was blended in extruder with 0–50% addition of styrene–ethylene/butylene–styrene (SEBS) and styrene–butadiene–styrene (SBS) block copolymers. Granulated blends were irradiated with electron beam (60 kGy) and 1 week later processed with injection molding machine. Properties of samples molded from irradiated and non-irradiated granulates were investigated using DSC, WAXS, MFR, SEM and mechanical and solubility tests. It was found that the SEBS based systems are more resistant to irradiation in comparison to similar blends with SBS copolymer. Such behavior can be explained by the presence of double bonds in elastic SBS block. Irradiation of PP-SBS blends leads to considerable structure changes of crystalline and amorphous PP phases and elastic SBS phase. It indicates creation of new (inter)phase consisting of products of grafting and cross-linking reactions. Irradiated PP-SBS blends show significant improvement of impact strength at low temperatures.     

Effects of thermal annealing on the viscoelastic properties and morphology of bimodal hard/soft latex blends

The effects of thermal annealing on the viscoelastic properties and morphology of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles with controlled sizes were investigated. The thermal and viscoelastic properties of as‐dried and annealed samples were investigated with differential scanning calorimetry and dynamic mechanical analysis (DMA). Throughout the thermal annealing, the latex blend morphologies were also followed with atomic force microscopy and transmission electron microscopy (TEM). A particulate morphology, consisting of hard particles evenly dispersed in a continuous soft phase, was observed in the TEM micrographs of the as‐dried latex blends and resulted in an enhancement of the mechanical film properties at temperatures between the α relaxations of the soft and hard phases in the DMA thermograms. As soon as the thermal annealing involved temperatures higher than the glass‐transition temperature of the hard phase, the hard particles progressively lost their initial spherical shape and formed a more or less continuous phase in the latex blends. This induced coalescence of the hard particles was confirmed by the association of the experimental viscoelastic data with theoretical predictions, based on self‐consistent mechanical models, which were performed by the consideration of either a particulate or cocontinuous morphology for the bimodal latex blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2289–2306, 2005     

Electrical properties and conductive mechanisms of immiscible polypropylene/Novolac blends filled with carbon black

Carbon black (CB)-filled immisicible thermoplastic/thermosetting polymer blends consisting of polypropylene (PP) and Novolac resin were reported in this paper. The PP/Novolac/CB blends with varied compositions and different processing sequences were prepared by melt-mixing method. The CB distribution, conductive mechanism and the relationship between morphology and electrical properties of the PP/Novolac/CB blends were investigated. Scanning electron microscopy (SEM), optical microscopy and extraction experiment results showed that in PP/Novolac blends CB particles preferentially localized in the Novolac phase, indicating CB has a good affinity with Novolac resin. The incorporation of CB changed the spherical particles of the dispersed Novolac phase into elongated structure. With increasing Novolac content, the elongation deformation of Novolac phase became more obvious and eventually the blends developed into co-continuous structure, which form double percolation and decrease the percolation threshold. When CB was initially blended with PP and followed by the addition of Novolac resin, the partial migration of CB from PP to the Novolac phase was possibly occurred. The addition of Novolac to PP evidently increases the storage modulus G′, loss modulus G″ and complex viscosity η^∗. The addition of CB to PP/Novolac blends further increase η^∗, and it increases with increasing CB loading, which was related to the change of composite morphology.