LLDPE Resins Research Articles

Research and production of antimicrobial polymer blends from thermoplastic and polyguanidine

Microorganisms are one of the main causes of food spoilage and diseases that seriously affect human health. Therefore, the development of materials with antibacterial ability to help repel diseases and epidemics, improve the quality of life and, in particular, ensure food safety and hygiene is receiving much attention. In this study, first, PE wax was selected as the resin matrix for grafting maleic anhydride (MAH) to obtain PEw-g-MAH. Then, PEw-g-MAH continued to be used as the frame for Polyhexamethylene guanidine (PHMG) grafting; the obtained material was PEw-g-PHMG. Finally, PEw-g-PHMG was mixed with LLDPE resin to make antimicrobial polymer blend materials and applied to produce antibacterial films used in preserving agricultural products. The mixing ratio amongst materials was investigated to attain suitable properties. The results determined the proportions of materials suitable for MAH and Styrene were 8 and 12%, PHMG and PEw-g-PHMG were 45 and 7%, respectively. At these ratios, the resulting polymer blend has mechanical and antimicrobial properties suitable for applying film packaging and food preservation.

Comprehensive branching analysis of polyethylene by combined fractionation and thermal analysis

AbstractLinear low density polyethylene (LLDPE) and low density polyethylene (LDPE) differ significantly in their branching types and branching distributions. For a comprehensive analysis, preparative temperature rising elution fractionation and/or preparative molar mass fractionation are used to fractionate typical LLDPE and LDPE bulk resins into narrowly distributed fractions. The chain structures of the bulk resins and their fractions are further analysed using SEC, crystallization analysis fractionation, DSC and high‐temperature HPLC to provide detailed information on short chain branching in LLDPE and long chain branching in LDPE. For LDPE it is shown that the multiple fractionation approach is a powerful source of sample libraries that may have similar molar masses and different branching structures or alternatively similar branching but different molar masses. The analysis of these library samples by thermal analysis provides a much deeper insight into the molecular heterogeneity of the samples compared to bulk sample analysis. © 2018 Society of Chemical Industry

Physicochemical analysis of linear low-density polyethylene composite films containing chemically treated rice husk

A study was conducted to determine the appropriate surface treatment for rice husks (RH) in polymer composite film to improve the physical properties relative to those of untreated RH/linear low-density polyethylene (LLDPE) film. Pulverized RH was treated with NaOH (RH-m) and acetic acid (RH-ac) to prepare composite films with LLDPE resin. The treated RH showed typical mercerization and acetylation, as confirmed by spectroscopic and thermal analysis methods. The RH-m sample was mercerized, allowing decomposition of hemicellulose and partially amorphous cellulose. The RH-ac sample was processed via acetylation inducing partial lignin decomposition. Field-emission scanning electron microscopy showed smaller gaps at the RH/LLDPE interface for RH-m and RH-ac compared to that with untreated RH, implying increased composite compatibility. RH-m in particular showed superior tensile strength (15.85 N/mm2), elongation (884%), Young’s modulus (60.01 N/mm2), and tear strength (7.71N/mm2) compared to untreated RH and RH-ac.

Evaluation of the environmental impact of portion bag for food packaging: a case study of Thailand

This study applied life cycle assessment methodology in evaluating environmental impact of portion bag. The objective of this study was to identify the hotspot of environmental impact through life cycle of portion bag. The options were proposed for improving environmental performance of the product. The system boundary was defined as cradle-to-grave which included the ethylene production, LDPE and LLDPE resins production, portion bag production, disposal, and transportation. All materials and emissions were calculated based on 1 piece of portion bag which weighed 2.49 g. IMPACT 2002+ was used for assessing environmental impact on SimaPro V8.2 software. The result found that the most of environmental impact was generated from LDPE and LLDPE resins which was used as raw material for producing portion bag. After normalization, non-renewable energy showed the highest potential to concern. This impact related directly to the natural gas drilling, ethane production, ethylene production, resin productions, and energy in all process. In conclusion, it should be suggested that the selection of bio-material for producing portion bag can play an important role to reduce the environmental impact. The research demonstrates the possible way and benefits in improving cleaner raw material and suitable way of product's end-of-life for producing green portion bag in the future.

Controlling Necking in Extrusion Film Casting Using Polymer Nanocomposites

ABSTRACTThe research described was concerned with the effect of layered-silicate-based organically modified nanoclay fillers on controlling the extent of necking in a polymer melt extrusion film casting (EFC) process. We show that a linear polythylene resin (such as a linear low-density polyethylene—LLDPE) filled with a very low percentage of well-dispersed (or intercalated) nanoclay displays an enhanced resistance to the necking phenomenon. In general, melt-compounded nanoclay-filled LLDPE resin formulations displayed a higher final film width (less necking), thus a lower final film thickness (greater draw down for the same draw ratio), and cooled down faster when compared to the base LLDPE resin. Incorporation of nanoclay filler in the mainly linear chain LLDPE resin led to significant modification of the melt rheological properties that, in turn, affected the melt processability of these formulations. Primarily, the intercalated nanoclay-filled LLDPE formulations displayed the presence of strain-hardening in unaxial extensional rheology. Additionally, the presence of well-dispersed nanoclay in the LLDPE resin led to a display of prominent extrudate swell indicating the presence of melt elasticity in such formulations. The presence of melt elasticity, as shown by shear rheology and strain-hardening, observed by uniaxial extensional rheology, contributed to the LLDPE nanoclay formulations displaying an enhanced resistance to necking for these films. It can be concluded that linear chain polymers susceptible to necking in an EFC process can be made more resistant to such necking by using nanoclay fillers at very low levels of loading.

Study of the effect of the molecular architecture of the components on the melt rheological properties of polyethylene blends

The influence of the molecular architecture of linear low-density polyethylene on melt miscibility with low-density polyethylene was investigated. Different LLDPE resins with variable type and content of branches were blended at a given composition with the same LDPE. The rheology and different data-treatment methods based on mixture models suggest that the melt blend morphology is strongly dependent on the molecular architecture of the matrix, particularly on the amount of short chain branches. The properties of the blends in which the LLDPE sample possesses a high content of branches can be predicted by the miscible blend additivity rule. The blends in which the LLDPE had the lowest branch content were completely immiscible. In these cases the rheological properties showed values that are higher than expected for miscible blends, as predicted by the Palierne model. The molar mass and the type of comomomer in LLDPE do not play an important role in the melt morphology of the blends at the composition studied. Thus the level of branching in LLDPE is revealed as the molecular feature with the strongest influence on melt miscibility with LDPE.

Effect of Interface Improving on Morphology and Properties of Coir Fiber/LLDPE Bio-Composites

The mechanical properties of coir fiber/line low density polyethylene (LLDPE) bio-composites were studied and micrographs of fracture surface of impact specimens for the composites were analyzed by scanning electron microscope (SEM). The flexural and impact strength of the composite with a compatilizer were higher than that of the composite without a compatilizer. The results of interface morphology of the composites with a compatilizer show better interfacial adhesion than that of the composites without one by SEM. That compatibility between the fiber and LLDPE resin is improved on, which is essential reason of rigidity and toughness increase of the composites.

A New Class of High-Performance Compostable Plastic Bags and Can Liners

Heritage Bag Company has developed compostable bags and liners, which are produced from composites utilizing polymer and mineral materials technology of Heritage Plastics, Inc. This product line is based on proprietary blends of different biodegradable polymers which have been modified using mineral reinforcement technology to produce a readily extrudable polymer composite. This modification yields polymers that can be readily processed for end-use products such as films and bags with characteristics very similar to those obtained with higher α-olefin LLDPE resins, yet which meet the degradability requirements of ASTM D 6400-04.

The Effect of Polymer Properties on the Mechanical Behavior and Morphological Characteristics of Cast Polyethylene Film for Stretch and Cling Film Applications

Polyethylene films, prepared from a range of mLLDPE, LLDPE, and ULDPE resins containing 4% polyisobutylene (PIB) from a masterbatch, are manufactured using a Killion cast film extrusion system. FTIR, DSC, and mechanical analysis techniques are used to investigate the effect of comonomer type, density, and melt flow index (MFI) on the mechanical performance, orientation, and crystallinity of these films. The study established that comonomer type and MFI are the greatest factors influencing the mechanical performance and crystallinity. Crystallinity has been found to be the most influential factor governing PIB migration in these films and this in turn is related to polymer type, density, and MFI.

Comparison of methods for characterizing comonomer composition in ethylene 1-olefin copolymers: 3D-TREF vs. SEC-FTIR

In this paper, two methodologies for determining comonomer composition in ethylene 1-olefin copolymers, namely three detectors coupled to a temperature rising elution fractionation unit (3D-TREF) and size exclusion chromatography coupled to a Fourier transfer infrared detector (SEC-FTIR), are examined and compared. Because the two methods are based on different separation mechanisms, insight into the resin's molecular architecture is gained from two entirely different, yet complementary perspectives. The choice of which method to use will be determined by the specific structure vs. property issue under study. Comparative results from the analysis of copolymers produced by Ziegler–Natta, chromium and metallocene catalysts show that both the methods are useful for characterizing LLDPE resins. However, the 3D-TREF method may offer more insight into the heterogeneity of resin blends, particularly when the blend components have similar molecular weights. Although some MW-dependency information of the temperature fractions can be ascertained via viscometer and light scattering detectors, SEC-FTIR is the more appropriate method to detect compositional heterogeneity in resin blends that are composed of two or more resins with the same copolymer compositions, but with different molecular weights.

Tensile Strength Characteristics of Polymer Melts

Abstract Two different methodologies were employed to determine tensile strength properties of two LDPEs and two metallocene LLDPE resins through capillary and Haul-off (Rheotens-like) measurements. It has been shown that the tensile strength properties obtained by both methods yield almost the same values. Moreover, these values can be correlated to the drawability in tubular film blowing for corresponding materials.

Blending of High-Performance LLDPEs with Butene-LLDPEs and LDPEs

Several high-performance LLDPE resins for film applications have been developed in the past few years through Advanced Ziegler–Natta or Single-Site catalysts. These new resins significantly improve the film properties of conventional Ziegler–Natta resins, but they are generally more costly and/or more difficult to process. A relatively simple strategy for addressing the cost and processability issues is via post-reactor blending, either with butene-LLDPEs in order to reduce cost, or with LDPEs in order to improve processability. Blending of high-performance resins has a generally detrimental effect on film strength properties, although there are exceptions in certain compositions. Viability of a certain blend composition thus hinges on a cost versus performance evaluation of the properties of interest. The present work focuses on the performance aspect, through a study of the effect of blending butene-LLDPEs and LDPEs on the optical and mechanical properties of Advanced Ziegler–Natta and metallocene-LLDPEs.

TRADE-OFFS IN BLOWN FILM LLDPE TYPE RESINS FROM CHROMIUM, METALLOCENE AND ZIEGLER-NATTA CATALYSTS

In this paper, the processing-structure-property (P-S-P) behavior and trade-offs observed with three LLDPE resins made from chromium, metallocene and Ziegler-Natta catalysts were examined and critically compared. The basic molecular and rheological properties were examined. The blown film performance of these resins was examined with respect to the effects of film thickness and molecular orientation on film properties. Also, the processability of these resins was compared through an examination of the typical extrusion and film blowing processing parameters. Finally, an attempt was made to highlight the advantages and disadvantages of each resin type as they apply to blown film applications. The results demonstrate that LLDPE resins from these various catalysts are dramatically different in nature, thereby resulting in different trade-offs with respect to their P-S-P behavior in film blowing.

Comparison of EVA and Polyolefin Plastomer as Blend Components in Various Film Applications

Ethylene vinyl acetate (EVA) copolymers at various%VA content and AFFINITY** polyolefin plastomers (POP) were evaluated as blend components in various film applications rich in LDPE and LLDPE. The EVA resin miscibility with LDPE or LLDPE decreased as the VA content increased so that high VA EVA resins were partially or completely immiscible with LDPE or LLDPE resins. Both POP resins were miscible with LDPE or LLDPE resins. The blown films of LDPE/POP blends gave lower heat seal initiation temperature and lower haze compared to LDPE/EVA blended films. This is due to immiscibility of Elvax 3165 (18% VA) and Elvax 3128 (9% VA) with the LDPE resin. The impact and tear resistance of the POP based blown films were also superior. Oriented films of blends of POP with LLDPE and ULDPE resins exhibited significantly lower haze compared to blends of 12% VA EVA with LLDPE and ULDPE resins. Again, this is due to partial immiscibility of 12% VA EVA with LLDPE and ULDPE resins. The oriented films of blends of POP with LLDPE and ULDPE resins exhibited similar shrinkage at 90'C compared to blends of 12% VA EVA with LLDPE and ULDPE resins.

Development of High Quality LLDPE and Optimised Processing for Film Blowing

Abstract The majority of LLDPE resins is processed via blown film extrusion techniques for various applications in the industrial and consumer packaging business. These LLDPE resins all have, independent of the molecular structure differences, the same intrinsic limitation in blown film extrusion processing. These limitations are: low output, high sensitivity to surface defects (stripes, sharkskin), high machine power requirement, need for large die gaps, lower bubble stability, and low melt strength. As a consequence, the more versatile—manufacturing and property wise—LLDPE resins are not used to their full potential. The industrial objective is therefore threefold: • develop a new LLDPE resin overcoming the above limitations, • develop a new flexible blown film extrusion line tailored to the new generation of LLDPE resins, • develop an efficient 3-D finite element simulation code to assist in the resin and blown film extrusion line development.

Quantification of channelling in polyethylene resin fluid beds using X-ray computer assisted tomography (CAT)

The determination of fluid distributions in fixed and fluidized beds was given a new dimension with the implementation of tomographic imaging techniques. Of particular interest is the time-averaged macroscopic determination of solids and gas in gas-phase polymerization reactors. The voidage distribution coupled with appropriate kinetic models can provide an estimate of deviation from expected fluid behaviour, which is due to the presence of hot spots or gas by-passing. In this study, the fluidization characteristics of commercially available LLDPE and HDPE resins were investigated using X-ray CAT scanning. The experiments were run in a small column with a diameter of 10 cm ( D) and variable bed heights at L D ratios of one, two and three. The fluidization velocities were varied between one and three times the minimum fluidization velocity for each sample. All experiments were performed at ambient conditions. The X-ray CAT scanner images describe the solid and gas distributions at a resolution of 400 μm by 400 μm in cross-section and 3 mm in thickness. Hundreds of images were collected and analysed. It is very important to note that in most cases the slice-average voidage is constant through the column length. However, there is considerable radial variability within each slice. This variability is measured as a function of position, and in fixed positions as a function of time. In this paper, we try to quantify these observations through comparisons of the voidage distribution of a fluid bed to the expected corresponding distribution of a uniform bed. Deviations from the expected mean are classified in distinct categories. The areas of consistently high gas concentration are identified as areas of gas channelling. Having identified these areas, we proceeded with the determination of the formation and propagation of gas channels in a fluid bed both in the spatial and temporal domains. We found that the simple fluid-bed systems we used in the laboratory exhibited a complicated gas channelling picture at relatively low L D and relatively low fluidization numbers. Channels can appear in the bed and can have a variety of characteristics and relative positions in the bed while the operating conditions vary only slightly. The implication of such channels in the operation of gas-phase polymerization reactors is also presented.

Monitoring the fluidization characteristics of polyolefin resins using X-ray Computer Assisted Tomography scanning

Flow visualization of chemical reactor phenomena was given a new direction with the implementation of process tomography techniques. These techniques can provide valuable information on flow phenomena in heterogeneous reactors. In particular, visualization and understanding of flow phenomena in gas phase polymerization reactors can aid us in achieving a better temperature distribution in the reactor and higher quality of products. In this study, the fluidization characteristics of a series of commercially available LLDPE, HDPE and IPP resins were investigated. The experiments were run in a small column of 10 cm in diameter (D) and variable bed heights (L), at L/D ratios of one, two and three. The fluidization velocities were varied between one and three times the minimum fluidization velocity of each sample. The particle size distributions varied from very narrow mesh sizes to full particle size distributions as they came out of commercial gas phase polymerization reactors. The resins also varied in sphericity. In several samples, there was some rubber present in the particles resulting in a “stickiness” characteristic of the resin. All experiments were performed at ambient conditions and inside the x-ray Computer Assisted Tomography (CAT) scanner facility. The CAT scanner images provided areal gas voidage distributions as a function of position and operating conditions at a resolution of 400 μm by 400 μm in cross section and 3 mm in thickness. A large number of images were collected and analyzed. Experimental results clearly established a set of fluidization experiments that gave relatively uniform voidage distributions, whereas other experiments had extremely non-uniform voidage distributions. Segregation and channeling were also observed under various operating conditions. It was found that certain regions of the bed were characterized by high voidage while others by very low voidage. These regions varied with experiments using the same resin but different velocities and L/Ds. The spatial variability of the voidage was also described in terms of statistical moments, frequency distributions and variograms. The voidage distributions were found to vary from wide unimodal to tri-modal of the same range for experimental conditions that, at first sight, did not appear to be significantly different. This paper describes the various categories of voidage distributions observed and provides some first correlations between voidage and operating parameters. A discussion of the implications of such phenomena to the performance of a gas phase polymerization reactor is also presented.

The effect of teflon™ coatings in polyethylene capillary extrusion

AbstractTwo LLDPE resins were used in this work to determine the critical conditions for the occurrence of wall slip and melt fracture in capillary extrusion. It was found that the polymer‐metal interface fails at a critical value of the wall shear stress of about 0.1 MPa and, as a result, slip occurs. At values of wall shear strees of about 0.18 MPa the extrudate surface appears to be matte, while small amplitude periodic distortions (sharkskin) appear on the surface of extrudates at wall shear stresses above 0.25 MPa. Using a special slit die, the polymer–wall interface was coated with Teflon™ in order to examine the effect of this coating on the processability of polyethylenes. It was found that use of Teflon™ promotes slip, thus reducing the power requirement in extrusion and, most importantly, eliminates sharkskin at high extrusion rates. © 1995 John Wiley & Sons, Inc.

Blown Film Extrusion of Post-Consumer Recycled Lldpe Film

In this work, the properties of blown film made from post consumer recycled material were studied. Post-consumer recycled LLDPE film was blended with a virgin LLDPE resin at several levels in a twin-screw ex truder, and the melt index, storage modulus, and loss modulus of these blends were measured. Using these blends, blown film experiments were performed according to a factorial design, and the films produced were tested for dart drop impact strength, cross and machine direction tear strength, and gauge unifor mity.

Peroxide modification of linear low‐density polyethylene: A comparison of dialkyl peroxides

AbstractA commercial‐grade LLDPE resin was cross‐linked using three different dialkyl peroxides, at three different concentrations. The peroxides were ranked in order of their Cross‐linking efficiency and their effectiveness at increasing the storage modulus of the virgin resin at the cure temperature. The chemical mechanism by which the cross‐linking occurs is shown to be closely related to the changes in concentrations of reactive vinyl species on the polyethylene molecules, which follows well with proposed mechanisms of previous publications. Finally, a direct relationship is shown to exist between the rate of peroxide decomposition and the rate of increase in storage modulus of the rubbery modified resin during the curing reaction. © 1993 John Wiley & Sons, Inc.