• Advances in materials Research
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• v.1 no.4
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• pp.245-268
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• 2012

Results of isothermal torsional oscillation tests are reported on melts of linear low density polyethylene and isotactic polypropylene. Prior to rheological tests, specimens were annealed at various temperatures ranging from $T_a$ = 180 to $310^{\circ}C$ for various amounts of time (from 30 to 120 min). Thermal treatment induced degradation of the melts and caused pronounced decreases in their molecular weights. With reference to the concept of transient networks, constitutive equations are developed for the viscoelastic response of polymer melts. A melt is treated as an equivalent network of strands bridged by junctions (entanglements and physical cross-links). The time-dependent response of the network is modelled as separation of active strands from and merging of dangling strands with temporary nodes. The stress-strain relations involve three adjustable parameters (the instantaneous shear modulus, the average activation energy for detachment of active strands, and the standard deviation of activation energies) that are determined by matching the dependencies of storage and loss moduli on frequency of oscillations. Good agreement is demonstrated between the experimental data and the results of numerical simulation. The study focuses on the effect of molecular weight of polymer melts on the material constants in the constitutive equations.

• Food Science and Preservation
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• v.10 no.2
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• pp.131-135
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• 2003

Bell pepper was packed with several plastic films, and investigated the quality Characteristics such as gas composition, weight loss, microbial load, soluble solid content, ascorbic acid and color during storage at 10$^{\circ}C$. Cast polypropylene (CPP), low density Polyethylene (LDPE), Polyolefin (MPD, PD961) and linear low density polyethylene (LLDPE) were used for this purpose. Oxygen concentration inside packages generally showed a 10∼14% after 1∼2 weeks, but package with CPP maintained above 15％ throughout the storage. Carbon dioxide concentration of CPP was above 2%, but other treatments showed below 2%. Weight loss of all treatments was below 3.0% after 5 weeks. Total microbial count showed a similar pattern compared to yeast and mold, and CPP maintained the highest microbial load after 3 weeks. Yellowness (b value) of bell pepper was generally increased throughout the storage, and MPD and PD961 were higher than other treatments.

• Korea-Australia Rheology Journal
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• v.14 no.1
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• pp.25-32
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• 2002

We report the first steps of a collaborative project between the University of Queensland, Polyflow, Michelin, SK Chemicals, and RMIT University, on simulation, validation and application of a recently introduced constitutive model designed to describe branched polymers. Whereas much progress has been made on predicting the complex flow behaviour of many - in particular linear - polymers, it sometimes appears difficult to predict simultaneously shear thinning and extensional strain hardening behaviour using traditional constitutive models. Recently a new viscoelastic model based on molecular topology, was proposed by McLeish and carson (1998). We explore the predictive power of a differential multi-mode version of the porn-pom model for the flow behaviour of two commercial polymer melts: a (long-chain branched) low-density polyethylene (LDPE) and a (linear) high-density polyethylene (HDPE). The model responses are compared to elongational recovery experiments published by Langouche and Debbaut (19c99), and start-up of simple shear flow, stress relaxation after simple and reverse step strain experiments carried out in our laboratory.

• Polymer(Korea)
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• v.25 no.5
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• pp.657-664
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• 2001

In this study. the effects of ${\gamma}$-irradiation on the crosslinking of low density poly ethylene (LLDPE) and linear low density polyethylene (LLDPE) containing crosslinking agents were investigated to find the degree of crosslinking in the polymer. The LDPE and LLDPE specimens were prepared by blending crosslinking agents with each polymers, and by hot-press-molding into a sheet at 13$0^{\circ}C$. The ${\gamma}$-irradiation was conducted at 50 to 150 kGy in nitrogen. The crosslinking percentage in these specimens was measured in relation to the irradiation dose and the type of crosslinking agents. The mechanical properties, thermal properties and crystallinity of specimens were examined as a function of irradiation dose as well. It was found that the degree of crosslinking of the irradiated specimens was increased with increasing irradiation dose and by the addition of crosslinking agents. The mechanical properties and thermal properties of specimens were improved in proportion to an increase in the degree of crosslinking. The crystallinity of original resin was decreased with increasing crosslinking density.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.195-198
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• 1998

In this paper, the physical and the volume resistivity properties due to linear low density polyethylene(LLDPE)/ethylene vinyl acetate(EVA) blends are studied. In order to measure the volume resistivity properties. the micro electrometer is used, the range of temperature and applying voltage are 25 to 120[$^{\circ}C$], form 100 to 1000[V] respectively. From FT-IR spectrum, LLDPE blended with EVA shows an absence of carbonyl and ether groups. From the experimental result of the volume resistivity properties, it is confirmed that the volume resistivity is decreased, which was attributed to the increase of molecular motions with the increase of temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.552-555
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• 1999

In this paper, the volume resistivity properties due to mixture ration of linear low density polyethylene(LLDPE) and ethylene vinyl acetate(EVA) are studied. Electrodes is composed of upper electrode 37(mm $\Phi$), guardring electrode(inner 55(mm $\Phi$ ), and lower electrode 87(mm $\Phi$ In order to measure the leakage current, We used electrometer and stable oven with temperature controller. Measurement method is to measure the leakage current of next specimen after applying the voltage according to 'Step Apply Methods' for ten minutes. In order to measure the volume resistivity properties, the micro electrometer is used, the range of temperature and applying voltage are 25 to 100[$^{\circ}C$] to 100[V] respectively.

• Macromolecular Research
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• v.9 no.6
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• pp.297-302
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• 2001

Rice starch was incorporated into linear low density polyethylene (LLDPE) using a Brabender Plastic-Corder internal mixer at a temperature of 140$\^{C}$ and 40 rpm. The starch loading was varied from 0 to 30% with 5 intervals. Studies on brabender torque development, mechanical properties and water absorption were investigated. The starch loading did not influence the brabender torque significantly. With respect to mechanical properties; the tensile strength and elongation at break decrease with increasing starch loading. The Young's modulus also increases with the starch filling. Mechanical properties were deteriorated as the starch absorbed moisture. The rate of water absorption was dependent on the starch filling in the composites. The scanning electron microscope (SEM) analysis was performed for the tensile fracture surfaces and it revealed the starch agglomeration and a poor dispersion of starch in the LLDPE matrix.

• Polymer(Korea)
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• v.27 no.5
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• pp.502-507
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• 2003

The thermal and physical properties of low density polyethylene melt-blended with Metallocene linear low density polyethylenes were investigated. Since the Metallocene polyethylenes have similar MW and MWD except m-LLDPE4, it can be said that the thermal behavior and mechanical properties of the blends depend upon the l-octene comonomer content. The melting behavior of LDPE/m-LLDPE1 blends shows two melting peaks with LDPE contents higher than 50%, while the other blends show only one melting peak. It was observed that the blends show higher crystallization temperature and higher crystallinity with lower comonomer content. Initial modulus of a blend exhibited the behavior proportional to the crystallinity and the elongation at break of the blends was increased with increasing the m-LLDPE composition. Melt indices of the blends decreased with increasing the comonomer content of Metallocene LLDPE. Melt Index values of the blends show negative deviation.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.370-376
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• 2012

We fabricated linear low density polyethylene (LLDPE) particles via crystallization from decalin solution. In the thermally induced phase separation (TIPS) process, formation of particles occurred during controlled cooling of LLDPE/decalin solution. Despite an increase of nucleation and growth rate for crystals at higher polymer concentrations, which generally results in larger particles than at lower concentration, the average diameter of LLDPE particles increased as LLDPE was more concentrated in decalin solution. In the FE-SEM micrographs, the observed particles from various concentrations were smaller than 10 ${\mu}m$, showing spherical morphologies. In addition to its effect on size, concentration of LLDPE had an broadening effect on the particle size distribution.

• Polymer(Korea)
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• v.32 no.5
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• pp.440-445
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• 2008

The failure mechanism and failure morphology of linear low density polyethylene (LLDPE) tubing under hydrostatic pressure were investigated. Microscopic observations using video microscope and scanning electron microscope indicate that the failure mode is a brittle fracture including cracks propagated from inner wall to outer wall. In addition, oxidation induction time and Fourier transform infrared spectroscopy results show the presence of exothermic peak and the increase in carbonyl index on the surface of fractured LLDPE tubing, due to thermal-degradation. An accelerated life test methodology and testing system for LLDPE tubing are developed using the relationship between stresses and life characteristics by means of thermal acceleration. Statistical approaches using the Arrhenius model and Weibull distribution are implemented to estimate the long-term life time of LLDPE tubing under hydrostatic pressure. Consequently, the long-term life time of LLDPE tubing at the operating temperature of $25^{\circ}C$ could be predicted and also be analyzed.