Hot tack of metallocene catalyzed polyethylene and low-density polyethylene blend

Films made of metallocene catalyzed polyethylene (mPE), low-density polyethylene (LDPE), and their blend were prepared to investigate how LDPE influences the hot tack of film. Experimental results showed hot tack is independent of film thickness. The addition of 30 wt % of LDPE can increase the hot tack of mPE film. The thermograms of differential scanning calorimetry (DSC) suggest the respective partial melting and recrystallization of those smaller size crystals at the bond forming and joint fracture stages play very important roles. The large amount of partial melting and high flow may induce a higher degree of molecular diffusion. Higher residual crystallinity and recrystallization at the hot tack testing process may induce higher resistant to bond fracture. Those two positive influences show that the mPE/LDPE film has the higher hot tack. The evidence from optical (higher optical transmission and lower haze) as well as viscoelastic (higher storage modulus and lower melt viscosity) properties further support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1769–1773, 1999     

Fracture behaviors of metallocene catalyzed polyethylene elastomer via peroxide crosslinking

Peroxide cured metallocene catalyzed polyethylene (mPE) has been prepared to form an elastomer. mPEs with two different levels of comonomer contents have been cured with various amounts of dicumyl peroxide. “Threshold” fracture energy is roughly proportional to the reciprocal square root of Young's modulus. The values of tear strength are generally two orders of magnitude larger than the results from cutting measurements. The cutting strength of mPE vulcanizates gives an intermediate value compared with crystalline plastics and conventional elastomers and is comparable with other evaluations of cutting strength for different crosslinking types of mPE and different types of materials, which further signifies the importance of crystalline yielding even in the nanofracture zone of deformation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ziegler-Natta/茂金属复合催化剂制备双峰聚乙烯

通过把茂金属催化剂负载在Ziegler-Natta催化剂上制备了ZM复合催化剂,在单一聚合反应器内研究了ZM催化剂用于乙烯聚合制备双峰聚乙烯的性能。考察了催化剂中茂金属化合物的含量、聚合过程中反应温度、助催化剂的用量和共聚单体1-己烯的用量对催化剂乙烯聚合性能的影响规律。结果表明：采用ZM催化剂可以在单反应器内催化乙烯聚合得到分子量分布呈双峰的聚乙烯,聚乙烯的分子量分布达到155,聚合活性可达2.52×10⁷ g/molMt·h。     

Properties of bamboo flour/high-density polyethylene composites reinforced with ultrahigh molecular weight polyethylene

In order to improve the properties of bamboo-plastic composites (BPCs), bamboo flour/high-density polyethylene (HDPE) composites were reinforced with ultrahigh molecular weight polyethylene (UHMWPE). The effects of UHMWPE on properties of composites were studied. The crystallinity of composites decreased slightly. Compared with non-UHMWPE added bamboo powder/HDPE composite, the composite with 6 wt % UHMWPE, showed decrease in water absorption to 0.41%, whereas its tensile strength and flexural strength increased to 34.51 and 25.88 MPa, respectively, a corresponding increase of 34.59 and 12.87%. The temperatures corresponding to initial degradation temperature (T_initial) and maximum degradation temperature (T_max) of the composite increased from 282.7 and 467.4 °C to 288.5 and 474.7 °C respectively. Scanning electron microscopic images showed that UHMWPE was well dispersed and fully extended as long fibers in the composite, forming a “three-dimensional physically cross-linked network structure,” which contributed to the improved properties of the composites. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48971.     

Miscibility and crystallization of metallocene polyethylene blends with polypropylene

The crystallization and morphology of very‐low‐density polyethylene (VLDPE) and ultra‐low‐density polyethylene (ULDPE) blends with isotactic polypropylene (PP) were studied by differential scanning calorimetry (DSC) and hot‐stage optical microscopy (HSOM) with polarized light. In particular, the isothermal crystallization of PP in molten PE was investigated. A polypropylene homopolymer was melt‐blended with six types of VLDPEs and ULDPEs, with variations in branch content and length and in molecular weight. All the blends contained 20% PP by mass. It was found that the crystallization temperatures of PP and PE changed in the blends, and the crystallization of PP was affected by branch length and content and by the molecular weight of the PE, indicating a certain degree of miscibility between PP and PE. The isothermal crystallization rate of PP decreased in the blends; in particular, the crystallization rate of PP was slower in the ULDPE with lower MFI, suggesting that crystallization of PP was hindered by PE and that its rate was regulated by the viscosity of ULDPE. HSOM images showed that a portion of the PP crystallized from molten PE, although phase separation was obvious, providing additional information on the miscible behavior between PP and VLDPEs (or ULDPEs). Furthermore, the miscible level between the PP and the ULDPEs was higher than that between the PP and the VLDPEs because the degree of change in the crystallization behavior of the PP and PE was greater in the PP–ULDPE blends. This was possibly a result of the higher branch content in the ULDPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1179–1189, 2003     

Biodegradation process of a blend of thermoplastic unripe banana flour—polyethylene under composting: Identification of the biodegrading agent

Starch‐based biodegradable polymers are obtained by incorporating plant‐derived polymers into plastics. This blending allows for a reduction in the polymer's resistance to microbial degradation. Assessing biodegradability is a key step in the characterization of newly designed polymers. Composting has been taken into consideration in waste management strategies as an alternative technology for plastic disposal. This study analyzed the biodegradability of an injection‐molded plastic material in which thermoplastic unripe banana flour (TPF) acts as a matrix (70%) and metallocene catalyzed polyethylene acts as a reinforcing filler (30%). This plastic was termed 70 TPF, and the structural, physical, and mechanical changes associated with its degradation were analyzed. The characterization of the microorganism that contributes to 70 TPF biodegradation was also performed. After composting, 70 TPF decreased in tensile strength and the TPF moiety in the blend was lost, greatly affecting the microstructure of the sample. Based on these indicators of degradation, this study identified the fungus Mortierella elongata as the microorganism responsible for the degradation of the plastic, a finding that supports the role of fungal communities in the biodegradation of designed materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42258.     

Processability,morphology and mechanical properties of wood flour reinforced high density polyethylene composites

Abstract

Wood flour reinforced high density polyethylene (HDPE) composites have been prepared and their rheological properties measured. The melt viscosity decreased as the processing temperature increased and the wood flour content decreased. A power law model was used to describe the pseudoplasticity of these melts. Adding wood flour to HDPE produced an increase in tensile strength and modulus. Composites compounded in a twin screw extruder and treated with a coupling agent (vinyltrimethoxysilane) or a compatibliser (HDPE grafted with maleic anhydride) exhibited better mechanical properties than the corresponding unmodified composites because of improved dispersion and good adhesion between the wood fibre and the polyalkene matrix. Scanning electron microscopy of the fracture surfaces of these composites showed that both the coupling agent and compatibiliser gave superior interfacial strength between the wood fibre and the polyalkene matrix.     

Chain transfer reaction in metallocene catalyzed ethylene copolymerization with allyltrimethylsilane

Summary In order to investigate the polymerization behavior of allytrimethylsilane as a comonomer, ethylene was copolymerized with allyltrimethylsilane at 80°C in toluene using methylaluminoxane (MAO) activated metallocene catalysts. The catalytic activity of the polymerization strongly depended on both the type of the catalysts and the concentration of allyltrimethylsilane. End group analysis of the copolymers by means of ¹H and ¹³C NMR spectroscopy revealed that allyltrimethylsilane rather act as a chain transfer agent in the copolymerization, even though considerable amount of allyltrimethylsilane was incorporated in the polymer chain with rac-Et(Ind)₂ZrCl₂ catalysts. The chain transfer reaction influence strongly the molecular weight and comonomer content of the copolymers. Received: 22 June 1999/Revised version: 9 September 1999/Accepted: 30 September 1999     

Thermoplastic corn starch reinforced with cotton cellulose nanofibers

This work evaluates the use of cotton cellulose nanofibers (CCN) as a reinforcing agent to prepare thermoplastic corn starch (TPS) matrix plasticized with 30 wt % of glycerol. The nanocomposites were filled with 0.5–5.0 wt % of CCN on a dry‐starch basis. The dried nanofibers were resuspended through the use of an ultrasonicator and then introduced in the fixed water formulation for obtaining TPS. The nanocomposites were compounded in a corotating twin‐screw extruder. Scanning transmission electron microscopy (STEM), field emission gun (FEG), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA), in air atmosphere, were used to characterize nanofibers, neat TPS, and nanocomposites. The results showed that the nanofibers had needlelike structure with an average length of about 135 ± 50 nm and an average diameter of about 14 ± 4 nm. The addition of CCN was effective to enhance the mechanical properties of neat TPS in compositions above 2.5 wt %, although some agglomeration could be observed. The resulting nanocomposites showed good structural stability, because the amylopectin transcrystallization phenomena on the surface of nanofibers had not occurred. Only a slight decrease in the crystallinity index and a minor increase in the water absorption in relation to neat TPS were observed. An increase in the thermal stability of TPS nanocomposites with respect to neat TPS was verified, but it was independent of the CCN content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of polyethylene using ultrasonic energy with a metallocene catalyst

Ethylene polymer was synthesized by the treatment of a metallocene catalyst Zr(CP)₂Cl₂ solution with ultrasonic energy. Ultrasonic energy irradiation was used to change the polymer structure of the formed polymer. Different ultrasonic energy irradiation times were applied to the metallocene catalyst solution. The ultrasonic energy had an effect on the average molecular weight, molecular weight distribution, and polymer productivity. A lower average molecular weight and a narrower molecular weight distribution were produced with a longer ultrasonic irradiation time. The polymer productivity was almost constant when the metallocene catalyst was treated with ultrasonic energy. Finer polyethylene particles were produced with longer ultrasonic irradiation times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 756–759, 2006     

限制几何构型茂金属/硼化物催化1-癸烯齐聚及其产物表征

用限制几何构型的茂金属催化体系2-Me4Cp-4,6-tBu2-PhOTiCl2/Al(iBu)3/Ph3C+B(C6F5)4-对1-癸烯的齐聚进行了研究。探讨了Al与Ti摩尔比和反应温度对聚合反应的影响。用GC和13CNMR表征了聚合物组成和结构。结果表明,聚合物主要是二聚物、三聚物、四聚物、五聚物。该齐聚物具有高黏度指数(VI=238)、低凝点(≤-62℃)的性质,是理想的润滑油基础油组分。     

Processing characteristics and mechanical properties of metallocene catalyzed linear low‐density polyethylene foams for rotational molding

The object of this work is to assess the suitability of metallocene catalyzed linear low‐density polyethylenes for the rotational molding of foams and to link the material and processing conditions to cell morphology and part mechanical properties (flexural and compressive strength). Through adjustments to molding conditions, the significant processing and physical material parameters that optimize metallocene catalyzed linear low‐density polyethylene foam structure have been identified. The results obtained from an equivalent conventional grade of Ziegler‐Natta catalyzed linear low‐density polyethylene are used as a basis for comparison. The key findings of this study are that metallocene catalyzed LLDPE can be used in rotational foam molding to produce a foam that will perform as well as a Ziegler‐Natta catalyzed foam and that foam density is by far the most influential factor over mechanical properties of foam. Polym. Eng. Sci. 44:638–647, 2004. © 2004 Society of Plastics Engineers.     

桥联茂金属催化1-癸烯聚合及其产物结构与性能

采用桥联茂金属催化体系rac-Et(1-Ind)₂ZrCl₂/Al(ⁱBu)₃/[Me₂NHPh]⁺[B(C₆F₅)₄]^-催化1-癸烯聚合,考察了茂金属浓度、Al/Zr摩尔比、B/Zr摩尔比、温度、反应时间对反应转化率、黏度和摩尔质量的影响.当反应条件为1-癸烯20mL、甲苯20mL、Zr/烯摩尔比8×10^-5、Al/Zr摩尔比80、B/Zr摩尔比1.5、温度80℃、反应时间1h时,转化率达到96.2%.采用¹³C NMR和¹H NMR表征了产物的结构,优化条件下所得的聚合产物具有高黏度指数(259)和低分子量分布(2.088),可作为理想的润滑油基础油的原料.     

A heat-bonded fibrous material from polyethylene

Conclusions The fundamental possibility of preparing a heat-bonded fibrous material from polyethylene has been established.It has been found that a heat-bonded fibrous material from polyethylene is inferior in basic consumer properties to material from copolyamide.It is recommended to use heat-bonded material from polyethylene for joining fabrics in the sewing industry.Translated from Khimicheskie Volokna, No. 1, pp. 32–33, January–February, 1990.     

Fabrication and characterization of 100% green composite: Thermoplastic based on wheat flour reinforced by flax fibers

Biocomposites having flax fibers as reinforcement in wheat flour based thermoplastic matrix were prepared by extrusion method. The fiber content of the composites varied from 0% to 20% w/w. The structure and morphology of the fiber and composites prepared were studied using X‐ray diffraction and scanning electron micrograph methods. The mechanical properties such as stress at failure, strain at failure, and tensile modulus were studied as a function of fiber content. The incorporation of fiber to the matrix increased the tensile properties and is maximum for the composite having a fiber loading of 20% w/w. Thermal stability of the fiber and the composite having various fiber content (0, 5, 10, 15, and 20% w/w) was analyzed by thermogravimetric method. There is no significant variation in the thermal stability of the composites. Finally, comparative studies of the mechanical properties were done to evaluate the efficiency of this new system. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Plastic deformation of low‐density polyethylene reinforced with biodegradable polylactide,Part 2: Creep characterization and modeling

The behavior of low‐density polyethylene (LDPE) and two blends prepared with polylactide (PLA) was determined by means of a novel video‐controlled testing method under stretching at constant true strain rate, under creep at constant true stress, and under creep at constant nominal stress. Most tests were performed at 23°C and 50°C. In this second part, the experimental data are modeled with the G'Sell‐Jonas phenomenological law expressing the axial true stress versus axial true strain and axial true strain rate. This model describes correctly the various deformation stages: (i) initial viscoelasticity, (ii) plastic yielding, and (iii) strain hardening up to rupture. It shows clearly the reinforcing effect of the PLA particles that increases the yield stress in stretching experiments and slows down the deformation kinetics under creep. It is shown how the local stress/strain behavior is related to the standard force/extension curves. Consequently, it is proposed that tensile tests at constant true strain rates should be systematically preferred to creep tests for the characterization of constitutive relations because they take much less time to be performed. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Crystallinity of biodegradable polymers reinforced with functionalized carbon nanotubes

Well-dispersed multiwall carbon nanotubes (MWCNTs) were prepared by grafting poly(L-lactide-co-ε-caprolactone) (PLACL) biodegradable copolymer onto the sidewall of hydroxylated MWCNTs using oligomeric L-lactide (LA) and ε-caprolactone (CL). After preparation of MWCNT/PLACL composites, the effect of functionalized MWCNTs on crystallinity of PLACL was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarized light optical microscopy (POM). The surface functionalization effectively improved the dispersion and adhesion of MWCNTs which acted as reinforcing filler in the PLACL polymer matrix and hence improved the physical and thermomechanical properties of the nanocomposites. The glass transition temperature (T _g) and the crystallinity of nanocomposites decreased in comparison with those of neat PLACL when the concentration of functionalized MWCNTs in nanocomposites was 0.5 wt%. With further increment in concentration of functionalized MWCNTs, the T _g of composites increased until the T _g of neat PLACL, and also the crystallinity of composites increased. The functionalized MWCNTs have no significant effect on the melting point of nanocomposites. The MWCNTs acted as heterogeneous nucleation points and increased the lamella size and therefore the crystallinity of PLACL. Furthermore, the larger agglomerated clusters of both kinds of MWCNTs (i.e., MWCNT-grafted-PLACL and pristine MWCNTs) are more effective than small clusters as nucleation points for growing the spherulites.     

茂金属催化剂/MAO催化1-癸烯齐聚合及其产物的结构与性能

用均相茂金属催化剂(n-Bu)Cp2ZrCl2/MAO对1-癸烯的齐聚合进行了研究。探讨了齐聚温度、Al/Zr摩尔比值、助催化剂、反应时间及催化剂浓度对齐聚反应的影响。 采用GC-MS、GC和13C NMR对齐聚物的组成和结构进行了表征。GC-MS和GC的分析结果表明所得齐聚物是由二聚体、三聚体、四聚体和五聚体组成。13C NMR分析结果表明1-癸烯齐聚时存在键接异构,主要是头-尾键接的1,2插入,也存在头-头、尾-尾键接的2,1插入。     

Graphene oxide reinforced polyvinyl alcohol/polyethylene glycol blend composites as high-performance dielectric material

Novel flexible dielectric composites composed of polyvinyl alcohol (PVA), polyethylene glycol (PEG), and graphene oxide (GO) with high dielectric constant and low dielectric loss have been developed using facile and eco-friendly colloidal processing technique. The structure and morphology of the PVA/PEG/GO composites were evaluated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV-vis spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The dielectric behavior of PVA/PEG/GO composites was investigated in the wide range of frequencies from 50 Hz to 20 MHz and temperature in the range 40 to 150 °C using impedance spectroscopy. The dielectric constant for PVA and PVA/PEG (50/50) blend film was found to be 10.71 (50 Hz, 150 °C) and 31.22 (50 Hz, 150 °C), respectively. The dielectric constant for PVA/PEG/GO composite with 3 wt% GO was found to be 644.39 (50 Hz, 150 °C) which is 60 times greater than the dielectric constant of PVA and 20 times greater than the dielectric constant of PVA/PEG (50/50) blend film. The PVA/PEG/GO composites not only show high dielectric constant but also show low dielectric loss which is highly attractive for practical applications. These findings underline the possibilities of using PVA/PEG/GO composites as a flexible dielectric material for high-performance energy storage applications such as embedded capacitors.