Linear Low-density Polyethylene Particles Research Articles

The fracture behavior of particle modified polypropylene – 3D reconstructions and interparticle distances

The fracture behavior and fracture mechanics at the very early stages of both ethylene-propylene-rubber (EPR) and linear low-density polyethylene (LLDPE) modified isotactic polypropylene (iPP) were investigated. For this purpose tensile tests of the respective samples were stopped at forces far below the yield point and subsequently 3D reconstructions of the fracture regions were performed. It was thus possible to obtain information about the distribution of the surface-to-surface interparticle distances of the EPR and LLDPE particles, the size of voids and cracks/crazes and also their position with respect to the EPR and LLDPE particles. A single quantitative parameter was introduced that characterizes the correlation between the interparticle distance and the formation of cracks/crazes. Whereas crack/craze formation occurred in EPR modified iPP, LLDPE modified iPP showed debonding of the particles from the matrix and cavitation. But despite the completely different fracture mechanisms, the surface-to-surface interparticle distance distribution, particle agglomeration and thus percolation theory seem to play a vital role in both cases, at least at the start of fracturing, confirming theories developed by Wu and Liang.

Core/shell morphologies in recycled poly(ethylene terephthalate)/linear low-density polyethylene/poly(styrene-b-(ethylene-co-butylene)-b-styrene) ternary blends

Compatibilizer plays very important roles in preparing high performance polymer composites, not only for the ternary immiscible polymer blends, but also for the recycled and reused of waste plastics mixture. Generally, the compatibilizers can be used as the toughening agent in blending polymer materials. In the present work, the poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) or maleic anhydride-grafted poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS-g-MA) acts as the compatibilizer and toughening agent for the preparation of R-PET/LDPE/SEBS (70/20/10) ternary blends. It must be pointed that the ternary blends are costlessly and conveniently prepared from the recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) through a melt blending in a co-rotating twin-screw extruder and injection moulded. The morphologies of the ternary blends are characterized by scanning electron microscopy (SEM). It was found that the blends contains reactive or non-reactive compatibilizer, the morphology originates from the LLDPE particles encapsulated by both SEBS and SEBS-g-MA. So, it results to the reduced interfacial tension between of the R-PET and SEBS-g-MA, in which the grafted chains of PET-g-SEBS-g-MA formed through in situ reaction between R-PET and SEBS-g-MA phases. Therefore, core–shell particles with smaller diameter disperse uniformly in the blends. Moreover, the good compatibilization and corresponding morphologies induce in balanced mechanical and thermal properties. DSC analysis show the dispersed phase particles could act as nucleating agent in the R-PET matrix, which results the improvement of the crystallization temperature. And it was also observed the decreased nucleation activity in graft copolymers in the R-PET/LLDPE/SEBS-g-MA blends. Notched Charpy impact strength and elongation at break are improved by the addition of compatibilizer.

Variation of Comonomer Content in LLDPE Particles with Different Sizes from an Industrial Fluidized Bed Reactor

Properties of linear low-density polyethylene (LLDPE) are highly influenced by molecular weight distribution and comonomer content. Our study quantifies comonomer content variation for LLDPE particles with different sizes. Powder from the fluidized-bed reactor was sieved to subsets with different sizes. FTIR showed a meaningful difference in average comonomer content among subsets. To study comonomer content distribution in each subset, successive self-nucleation and annealing (SSA) thermal fractionation via differential scanning calorimetry (DSC) was performed. This study showed that each subset not only differs in the average comonomer content but also in comonomer content distribution. Particles with a median diameter of 1500 μm had the highest average comonomer content, which was different from that of the final product. Minimum average comonomer content and narrowest comonomer distribution was observed in the smallest particles with median diameter of 750 μm and high molecular weight.

Experimental study on the influence of bed material on the scaling of solids circulation patterns in 3D bubbling gas–solid fluidized beds of glass and polyethylene using positron emission particle tracking

The time-averaged solids velocity profiles in a freely bubbling, three dimensional, gas–solid fluidized bed have been experimentally quantified for two different bed materials and different bed aspect ratios at different superficial gas velocities by performing positron emission particle tracking (PEPT) experiments. A cylindrical fluidized bed with an inner diameter of 0.306m was filled with either glass beads with a diameter of 400–600μm or with linear low density polyethylene (LLDPE) particles with a diameter of 1000–1300μm, having approximately the same ratio of Ar/Remf, trying to realize dynamic similarity. Fluidization of both bed materials showed Geldart B type behavior. At lower superficial gas velocities two distinct vortices appear above each other for both types of bed material; when the superficial gas velocity is increased, the lower vortex disappears and the top vortex spans the entire height of the bed. Although qualitatively the same phenomena were observed for both bed materials, the time-averaged solids phase circulation rate in the fluidized bed filled with LLDPE particles was significantly higher than the time-averaged solids phase velocity in the fluidized bed filled with glass beads, despite the similar ratio of Ar/Remf. When the bed aspect ratio is increased from 1 to 1.5, the vortices become elongated without altering the solids circulation rate. Differences in the particle–particle collisional properties (coefficients of restitution and particle friction coefficients) may be the cause of the observed quantitative differences in the bed hydrodynamics via their influence on the bubble characteristics.

Mechanical, Thermal, and Morphological Properties of Polylactic Acid/Linear Low Density Polyethylene Blends

Melt blending of polylactic acid (PLA) and linear low density polyethylene (LLDPE) was performed to investigate the effects of LLDPE loadings on the morphology, mechanical and thermal properties of PLA/LLDPE blends. LLDPE was blended with PLA from 5—15 wt% and prepared by counterrotating twin-screw extruder followed by injection molding into test samples. The mechanical properties of the blends were assessed through tensile, flexural and impact testings while thermal properties were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis. Scanning electron microscope was used to study the dispersion and particle size of LLDPE in PLA matrix. The impact strength of PLA improved by 53% with addition of 10 wt% LLDPE. However, the tensile modulus and strength, and elongation at break of PLA/LLDPE blends decreased with increasing weight ratio of LLDPE. Similarly, flexural modulus and strength also dropped with addition of LLDPE. DSC results showed that glass transition temperature (Tg) and crystallinity (X c) of PLA increased with blending of LLDPE. The LLDPE particles size was seen to increase with increasing loadings of LLDPE which explains the unexpected decrease of impact strength after 10 wt%.

Thermal, electrical, and mechanical properties of Si3N4 filled LLDPE composite

AbstractSilicon nitride (Si3N4) filled linear low‐density polyethylene (LLDPE) composite was prepared. The effects of Si3N4 filler content, dispersion, and LLDPE particle size on the thermal conductivity, and Si3N4 filled content on the mechanical and electrical properties of Si3N4 reinforced LLDPE composites prepared using powder mixing were investigated. The results indicate that there existed a unique dispersion state of Si3N4 particles in LLDPE, shell‐kernel structure, in which Si3N4 particles surrounded LLDPE matrix particles. With increasing filler content and LLDPE particles size, thermal conductivity increased, and reached 1.42 W/m K at 30 vol% of filler, seven times as that of unfilled LLDPE. Furthermore, the examinations of Agari model demonstrate that larger size LLDPE particles form thermal conductive networks easily compared with smaller ones. The values predicted by theoretical model underestimate the thermal conductivity of Si3N4/LLDPE composites. In addition, the composites still possessed rather higher electrical resistivity and dielectric properties, but the mechanical properties decreased. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Super‐ductile PBT alloy with excellent heat resistance

AbstractA super‐ductile PBT alloy with excellent heat resistance was successfully fabricated by reactive blending of poly(butylene terephthalate) (PBT) with poly(ethylene‐co‐glycidyl methacrylate) together with linear low density polyethylene (LLDPE) and hydrogenated styrene‐butadiene‐styrene block copolymer (SEBS). It possesses a unique tensile stress–strain curve with no yielding point and large elongation at break, moreover, the alloy did not show serious deterioration of the mechanical properties by high temperature annealing at 150°C for 96 h. The structure‐properties relationship is discussed on the basis of transmission electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, and wide‐angle X‐ray diffraction analysis. The outstanding ductile nature seems to come from the negative pressure effect of LLDPE (or LLDPE/SEBS) particles that dilates the PBT ligament matrix to enhance the local segment motions. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.

Statistical and deterministic chaos analysis of pressure fluctuations in a fluidized bed of polymer powders

The absolute and differential pressure fluctuations in gas-solid fluidized beds have been analyzed by statistical and deterministic chaos methods. Linear low-density polyethylene (LLDPE) particles with a mean diameter of 1.23 mm were used as a fluidizing material. The statistical methods are composed of the mean, standard deviation, skewness and kurtosis, and the deterministic methods are composed of autocorrelation, mutual information function, pseudo-phase space and correlation dimension. The minimum slug velocity of LLDPE particles is found to be 0.34 m/s by using the statistical and deterministic methods. As slugs appear and grow with increasing gas velocity, pressure fluctuations in the fluidized bed of LLDPE are oscillated and more periodic.

Properties of uncompatibilized and compatibilized poly(butylene terephthalate)-LLDPE blends

In this work, blends of poly(butylene terephthalate) (PBT) and linear low-density polyethylene (LLDPE) were prepared. LLDPE was used as an impact modifier. Since the system was found to be incompatible, compatibilization was sought for by the addition of the following two types of functionalized polyethylene: ethylene vinylacetate copolymer (EVA) and maleic anhydride-grafted EVA copolymer (EVA-g-MAH). The effects of the compatibilizers on the rheological and mechanical properties of the blends have been also quantitatively investigated. The impact strength of the PBT–LLDPE binary blends slightly increased at a lower concentration of LLDPE but increased remarkably above a concentration of 60 wt % of LLDPE. The morphology of the blends showed that the LLDPE particles had dispersed in the PBT matrix below 40 wt % of LLDPE, while, at 60 wt % of LLDPE, a co-continuous morphology was obtained, which could explain the increase of the impact strength of the blend. Generally, the mechanical strength was decreased by adding LLDPE to PBT. Addition of EVA or EVA-g-MAH as a compatibilizer to PBT–LLDPE (70/30) blend considerably improved the impact strength of the blend without significantly sacrificing the tensile and the flexural strength. More improvement in those mechanical properties was observed in the case of the EVA-g-MAH system than for the EVA system. A larger viscosity increase was also observed in the case of the EVA-g-MAH than EVA. This may be due to interaction of the EVA-g-MAH with PBT. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 989–997, 1999