Microstructural Evolution in Linear Low Density Polyethylene During Peroxide Modification: A Monte Carlo Simulation Study

The kinetics of crosslinking reaction of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) using dicumyl peroxide (DCP) as the initiator and tetrakis [methylene 3-(3’,5’-di-t-butyl-4’-hydroxyl)propanoate] (Irganox 1010) as the inhibitor were studied using Brabender Plasti-Corder (BPC) and Differential Scaning Calorimeter (DSC). The crosslinking reaction in the absence of inhibitor was found to be first order with respect to initiator concentration, while in the presence of inhibitor, the reaction was first order with respect to initiator concentration and 0.21-0.31 with respect to inhibitor concentration at 446 K for BPC and 413 K for DSC. In addition, the rate constant in the presence of inhibitor was found to be around three time lower than that in the absence. The activation energy of crosslinking reaction of LDPE and LLDPE were 118 and 112 kJ/mol, respectively for BPC technique and 184 and 176 kJ/mol, respectively for DSC technique. The pre-exponential factor of crosslinking reaction of LDPE and LLDPE were respectively 3.23 x 10¹¹ and 0.82 x 10¹¹ sec⁻¹ for BPC technique and 3.56 x 10¹⁹ and 3.64 x 10¹⁸ sec⁻¹ for DSC technique. The fraction of termination was determined and found that approximately 65% was terminated by combination of polymer radicals, while 35% was terminated by disproportionation and cyclization. The amount of DCP higher than 1.6%w/w used for the crosslinking reaction gave the degree of crosslinking in polymer greater than 80%. When 0.1-0.2%w/w of Irganox 1010 was used in the preparation of compound LDPE or LLDPE containing about 2%w/w DCP, the degree of crosslinking was constant at more than 80%. For the Iragox 1010 concentration greater than 0.2%w/w, the degree of crosslinking decreased with increasing inhibitor concentration.

Through this paper an experimental investigation has been done. The composites of different reinforced material having significantly good strength and improved properties are prepared. A comparative study was performed among LLDPE with non-woven fabric, LLDPE and non-woven fabric reinforced with rice husk, LLDPE with non- woven fabric and ash of rice husk. Linear Low Density Polymer (LLDPE) is used as base material in this fabrication process. LLDPE is mixed with the non-woven fabric in different percentage composition by weight in addition to the other natural reinforcement material (rice husk). Further an experiment was performed to calculate the mechanical properties like tensile strength, Melt flow Index (MFI), flexural strength, hence a comparative study of composite with different types of reinforcement was done to investigate the effect of mixing of different reinforcement material. Results shows that LLDPE with non-woven fabric (15 %) have less strength as compared to LLDPE with non-woven fabric and rice husk (10 %) and LLDPE with non-woven fabric and ash of rice husk (5 %). Water absorption characteristics are studied following ASTMD 570, results shows that LLDPE absorbs 0.15 per cent water, followed by LLDPE with rice husk (0.03 %) and LLDPE with ash (0.038 %).

Trade-offs in Blown Film Processing-Structure-Property Behavior of LLDPE Type Resins from Chromium, Metallocene and Ziegler-Natta Catalysts

Linear low density polyethylene (LLDPE) surface was modified by water plasma treatment to functionalized with oxygen-containing functional groups and to improve wettability. The LLDPE surface was treated at 10 and 20 W discharge power at various exposure times. A laboratory scale Megatherm radio frequency (RF) plasma apparatus that operates at 27 MHz was used to generate the water plasmas. Comparative studies were also made on LLDPE by using Argon plasma discharge followed by exposure to oxygen. The changes in chemical structure of the LLDPE polymeric chain upon plasma treatment were characterized by FTIR and XPS techniques. The selectivity of trifluoroacetic anhydride (TFAA) toward hydroxyl groups is used to quantify the hydroxyl groups formed on the polymer surface upon plasma treatment. The surface wettability of the samples was evaluated by measuring water contact angle of the samples before and after modification. In an attempt to understand the effect of surface modification of polymers on organopolysiloxane coating, selected samples were coated with SIGMACOTE. After exposition to the plasma discharge a decline in water contact angle were observed. FTIR and XPS measurements indicate an oxidation of degraded polymeric chains and creation of hydroxyl, carbonyl, ether, ester and carboxyl groups. Chemical derivatization with TFAA of water plasma treated polymer surfaces has shown that under the conditions employed, a very small (less than 5%) of the oxygen introduced by the water plasma treatment was present as hydroxyl group. The XPS results revealed that, under the plasma condition utilized, the surface modification of LLDPE using water plasma improves the wetting of polysiloxane onto the LLDPE surface.

Melt blending of linear low density polyethylene (LLDPE) and polylactide (PLLA) was performed in an extrusion mixer with post extrusion blown film attachment with and without compatibilizer-grafted low density polyethylene maleic anhydride. The blend compositions were optimized for tensile properties as per ASTM D 882-91. Based on this, LLDPE 80 (80 wt% LLDPE & 20 wt% PLLA) and M-g-L 80/4 (80 wt% LLDPE, 20 wt% PLLA and 4 parts compatibilizer per hundred parts of resin) were found to be an optimum composition. FTIR reveals that the presence of compatibilizer shifts carbonyl peak hence some increase in interaction between LLDPE and PLLA. Morphological characteristics of the fracture surface of with and without compatibilizer blends were examined by scanning electron microscopy. It shows that use of compatibilizer enhances the dispersions of PLLA in LLDPE matrix. Thermogravimetric (TG) analysis of blends shows the M-g-L 80/4 blend has higher thermal stability among studied blends. The degradation study under different pH of soil compost gives that in alkaline condition and the presence of compatibilizer was favorable for degradation. This blend may be used for packaging application.

In this study, linear low density polyethylene (LLDPE) was grafted and crosslinked by reactive extrusion melt compounding using different silane concentration with and without the presence of montmorillonite (MMT) nanoclay. The effects of different silane concentration and the addition of nanoclay filler on the degree of crosslinking, mechanical, thermal, rheological, and morphological properties were investigated and reported. Gel content results for all crosslinked samples were found to increase with increasing silane concentration. Tensile strength and Young's modulus of crosslinked LLDPE samples increased with increasing silane concentration compared to neat LLDPE; while the crosslinked LLDPE samples containing nanoclay have achieved higher tensile strength and Young's modulus, indicating strong interfacial interaction between silane grafted LLDPE matrix and nanoclay. However, the decrease of elongation at break for all crosslinked samples were observed compared to neat LLDPE. A reduction in the degree of crystallinity for crosslinked samples, particularly crosslinked samples containing nanoclay, was shown by thermal analysis results; whereas the melting temperature did not change significantly with increased silane concentration and subsequent addition of nanoclay. Thermogravimetric analysis results have revealed significant thermal stability improvement for neat LLDPE with increased silane concentration. Furthermore, crosslinked samples containing nanoclay have achieved better thermal stability compared to crosslinked samples without nanoclay. At lower frequency, it was found that viscosity, and storage modulus of neat LLDPE increased with increased silane concentration due to crosslinking and further addition of nanoclay into crosslinked LLDPE. The transmission electron microscopy results confirmed the intercalated structure of the nanocomposite for the crosslinked samples containing nanoclay.

The composite of linear low density polyethylene (LLDPE) with carbon black (CB) and inorganic flame retardant (aluminum hydroxide, Al(OH)3) was prepared by melt‐blending method. The effect of cross‐linking on the stability of positive temperature coefficient (PTC) of composite and the elimination of negative temperature coefficient (NTC) of composite were investigated. LLDPE was chemically cross‐linking with different contents of initiator (dicumyl peroxide, DCP). The cross‐linking effects of composite were analyzed by gel content analysis, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). By the effect of DCP, not only the composite appeared a high PTC intensity, but also the NTC effect of composite was eliminated. In this investigation, the optimum PTC intensity of composite reached 5.87 orders of magnitude for the composition of LLD0.l0C33.7A28, and the PTC transitional temperature of composite decreased with increasing of DCP content. In addition, the good reproducibility of composites was proved by thermal cycling, and successfully passed the test of over‐voltage resistance.

Mechanical properties of blends of low density with linear low density polyethylene

A reactive type dripping agent, glycerol monolauric acid monoitaconic acid diester (GLID) was synthesized in our laboratory. Grafting-copolymerization of linear low density polyethylene (LLDPE) with GLID was carried out by using β-ray irradiation in air in a twin-screw extruder. FT-IR was used to characterize the formation of grafting copolymer and evaluate their degree of grafting. The effects of monomer concentration, reaction temperature and screw run speed on degree of grafting were studied systematically. Crystallization rates of grafted LLDPE were faster than that of plain LLDPE at a given crystallization temperature. The tensile properties and light transmission of blown films were determined. Comparing with neat LLDPE film, no obvious changes could be found for the tensile strength, elongation at break and right angle tearing strength of LLDPE-g-GLID film. Acceleration dripping property of film samples was investigated. The dripping duration of LLDPE-g-GLID film and commercial antifog dripping film at 60° C were 69 days and 17 days, respectively.

Selected grades of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) were melt‐mixed and the physical, mechanical and rheological properties evaluated. The blends were found to combine the good mechanical properties of LLDPE and processing properties of LDPE. The effect of crosslinking the blends with dicumyl peroxide (1 phrParts per hundred rubber ) was also investigated. The level of crosslinking increased with increase in LLDPE content. While the mechanical properties of the crosslinked blends were more uniform, the physical properties controlled by the crystallinity of the polymer, such as density, hardness and volume loss on abrasion, decreased on crosslinking.

Adhesive effect of linear low-density polyethylene gels on polyethylene moldings

A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.

Oriented structure and anisotropy properties of polymer blown films: HDPE, LLDPE and LDPE

Thermo-oxidative degradation study of melt-processed polyethylene and its blend with polyamide using time-resolved rheometry

The rheological properties of linear low density polyethylene (LLDPE) were modified by irradiation in order to reduce or eliminate the unstable region (spurt) on the flow curve. Three different types of irradiation source (gamma ray, electron beam and UV light) were used to introduce the oxygen-containing groups into molecular chains of LLDPE, and consequently attain chain scission without any chemical additives resulting in smooth flow without any evidence of instability. This was proved by FTIR and contact angle measurements. Further, irradiation treatment should lead to increased polarity of polyethylene, and thus to increased adhesion between the polymer and polar fillers. Therefore, LLDPE filled with sericite–tridymite–cristobalite (STC) was investigated. Although the viscosity changes were rather negligible, a positive effect was seen during mixing, where torque, necessary to disperse the powder homogeneously in the polymer melt, was dramatically reduced, especially in the case of gamma-irradiated samples.