Preparation of thermoplastic vulcanizates based on waste crosslinked polyethylene and ground tire rubber through dynamic vulcanization

An environmental‐friendly approach called high‐shear mechanical milling was developed to de‐crosslink ground tire rubber (GTR) and waste crosslinked polyethylene (XLPE). The realization of partial devulcanization of GTR and de‐crosslinking of XLPE were confirmed by gel fraction measurements. Fourier transform infrared spectral studies revealed that a new peak at 1723.3 cm^?1 corresponds to the carbonyl group (? C?O) absorption was appeared after milling. The rheological properties showed that the XLPE/GTR blends represent lower apparent viscosity after mechanical milling, which means that the milled blends are easy to process. Thermoplastic vulcanizates (TPVs) could be prepared with these partially de‐crosslinked XLPE/GTR composite powders through dynamic vulcanization. The mechanical properties of the XLPE/GTR composites increased with increasing cycles of milling. The raw XLPE/GTR blends could not be processed to a continuous sheet. After 20 cycles of milling, the tensile strength and elongation at break of XLPE/GTR (50/50) composites increased to 6.0 MPa and 185.3%, respectively. The tensile strength and elongation at break of the composites have been further improved to 9.1 MPa and 201.2% after dynamic vulcanization, respectively. Re‐processability study confirmed the good thermoplastic processability of the TPVs prepared. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and mechanical properties of uncrosslinked and chemically crosslinked polyethylene/ethylene vinyl acetate copolymer blends

Uncrosslinked and chemically crosslinked binary blends of low‐ and high‐density polyethylene (PE), with ethylene vinyl acetate copolymer (EVA), were prepared by a melt‐mixing process using 0–3 wt % tert‐butyl cumyl peroxide (BCUP). The uncrosslinked blends revealed two distinct unchanged melting peaks corresponding to the individual components of the blends, but with a reduced overall degree of crystallinity. The crosslinking further reduced crystallinity, but enhanced compatibility between EVA and polyethylene, with LDPE being more compatible than HDPE. Blended with 20 wt % EVA, the EVA melting peak was almost disappeared after the addition of BCUP, and only the corresponding PE melting point was observed at a lowered temperature. But blended with 40% EVA, two peaks still existed with a slight shift toward lower temperatures. Changes of mechanical properties with blending ratio, crosslinking, and temperature had been dominated by the extent of crystallinity, crosslinking degree, and morphology of the blend. A good correlation was observed between elongation‐at‐break and morphological properties. The blends with higher level of compatibility showed less deviation from the additive rule of mixtures. The deviation became more pronounced for HDPE/EVA blends in the phase inversion region, while an opposite trend was observed for LDPE/EVA blends with co‐continuous morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3261–3270, 2007     

Dynamic vulcanization of recycled milk pouches (LDPE–LLDPE) and EPDM blends using dicumyl peroxide

The viability of thermomechanical recycling of post‐consumer milk pouches (blend of low‐density polyethylene (LDPE) and linear low‐density polyethylene (LLDPE)) and its scope for suitable engineering applications were investigated. The effects of blending with ethylene‐propylene‐diene monomer (EPDM) rubber and subsequent curing using dicumyl peroxide (DCP) on the macromolecular structure and properties of recycled polyethylene (PE) blends were studied. The crosslinking efficiency of recycled PE/EPDM blends and possible thermooxidative degradation of recycled polymer upon peroxide curing was assessed using torque and gel content measurements along with infrared spectroscopic analysis. Both the torque and gel content of the blends varied with DCP crosslinking reactions and also were affected by oxidative degradation. In view of the electrical application area of this recycled blend material, the dielectric breakdown strength and volume resistivity were measured. The mechanical performance and thermal stability of recycled PE/EPDM blends improved with progressive crosslinking by DCP but deteriorated somewhat at higher DCP dose. Scanning electron microscopy showed good interface bonding between recycled polymer and dispersed EPDM phase in the cured blends compared to the non‐cured blends. Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of cross‐linkable poly(phthalazinone ether ketone)s

A novel class of crosslinkable poly(phthalazinone ether ketone)s with relative high molecular‐weight and good solubility were successfully synthesized by the copolymerization of bisphthalazinone containing monomer, 3,3′‐diallyl‐4,4′‐dihydroxybiphenyl and 4,4′‐di‐ fluorobenzophenone. The synthesized polymers with inherent viscosities in the range of 0.42 to 0.75 dL/g can form flexible and transparent membranes by casting from their solution. The crosslinking reaction of these polymers can be carried out by thermally curing of the virgin polymers in or without the presence of crosslinking agent. The experimental results demonstrated that the crosslinking reaction also occurred to some extent during the polymerization. The crosslinked polymers exhibited equivalent glass transition temperature (T_g) at lower crosslinking density, and showed higher T_g than virgin polymers at higher crosslinking density. The crosslinked high‐temperature polymer can be used as the base material for high temperature adhesive, coating, enamel material, and composite matrices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Thermal and mechanical properties of silane‐grafted water crosslinked polyethylene

The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, with 0.10 phr of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5‐Dimethyl‐2,5‐di (tert‐butyl‐peroxy)‐hexane (DHBP), it was found that the grafting effect was improved; however, as Di(2‐tert‐butylperoxypropyl ‐(2))‐benzene (DIPP) or excess DHBP was used, LLDPE was supposed to cause self‐crosslinking, which reduced the grafting effect of silane and was invalid in the processing of extrusion. In this study, vinyl trimethoxysilane (VTMS) was grafted onto various polyethylenes (HDPE, LLDPE, and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to crosslink utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to crosslink during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for crosslinked LDPE and LLDPE. Mechanical and thermal properties of the crosslinked PE are much better than that of uncrosslinked PE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2383–2391, 2005     

Rheological and molecular properties of organic peroxide induced long chain branching of recycled and virgin high density polyethylene resin

Commercial blow molding grade recycled high density polyethylene (R‐HDPE) and blow molding grade virgin high density polyethylene (V‐HDPE) were reactively extruded with various compositions (0.00–0.15% wt/wt) of different peroxides in a twin screw extruder. The aim was to produce the extended chain mechanism of a blow molding grade HDPE photopolymer—a polymer resin comprising a significant part of the post consumer recycled plastic stream in Australia. In shear rheological tests, the modified material exhibited an increase in viscoelastic properties and complex viscosity compared to unmodified counterparts. Higher extent of viscoelastic properties enhancement was observed with 1, 3 1, 4 BIS (tert‐butylperoxyisopropyl) Benzene (OP2). This could be attributed to the higher degree of branching. The weight average molecular weight of the all modified materials and its molecular weight distribution (MWD) widened with peroxide modification. These results also support that formation of branching dominates the modification process at molecular level. Increase in branching index (g′) with increase in peroxide composition also confirmed higher degree of branching. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Compatibilization of polystyrene and low density polyethylene blends by a two-step crosslinking process

A new method has been developed to compatibilize the blends of polystyrene (PS) and polyethylene (PE). Polyethylene is first crosslinked partially by using a small amount of dicumyl peroxide (DCP) in a mixer at 165°C. Then the crosslinked PE is melt-blended with PS for another 5 min. Finally, a styrene–butadiene–styrene block copolymer (SBS) is added to the melt and mixed for another 5 min. We refer to this special procedure as the two-step crosslinking process. During the final mixing step of this process, the residual free radicals in the PE react with SBS. The crosslinking that occurs between PE and SBS has a significant impact on the mechanical properties of the blends including the impact strength, the tensile modulus, and the elongation-at-break. Scanning electron microscopy (SEM) results indicate that the interfacial adhesion is increased significantly, even though the domain sizes have not changed significantly in comparison with the non-crosslinked system. Transmission electron microscopy (TEM) results indicate that a thin SBS interfacial layer fully encapsulates the PE particles. This method could also be applied to other blend systems containing at least one component and a compatibilizer that are crosslinkable.     

Moisture crosslinking process for foamed polymers

Alkoxysilanes can be grafted onto an ethylene homopolymer or copolymer to give a moisture crosslinkable polymer. Moisture crosslinking has many benefits over peroxide‐ or irradiation‐induced crosslinking. Simple, conventional equipment allows processing with lower capital investment and less manufacturing space. The moisture crosslinking process permits conventional thermoplastic processing after the initial grafting process to give greater flexibility in the types of applications for this crosslinking technique. In foaming processes, silane crosslinking is compatible with most types of conventional blowing agents and other additives. The combination of silane crosslinking with metallocene polyethylene technology has given rise to a broad range of crosslinked polyolefin materials, including flexible, rigid, open, and closed cell foams. Good quality foams with very low densities, approaching 1 lb/ft³ (16 kg/m³), are possible. The advantages of silane crosslinking technology have opened many new markets for polyethylene foams.     

Film blowing of silane‐modified polyethylene

The grafting of vinyltriethoxysilane (VTES) onto polyethylene (PE) with the help of small amounts of peroxides was investigated to film‐blow these modified materials. The degree of crosslinking was kept very low to achieve good melt processability and improved mechanical properties. The possibility of obtaining modified PE films with improved properties and regularly distributed crosslinking with a single processing step demonstrates the uniqueness of this study. The additive concentration was established through preliminary studies; with a batch mixer, it was possible to process the modified PE in the film‐blowing operation. Water treatment of the modified films after film blowing allowed for improved properties without the processability being affected. The modification of PE was followed with mechanical, rheological, and extraction tests and with calorimetric analyses. The variations of the main mechanical properties of the films were very important from an application point of view. The elastic modulus and tear strength of the films for both extrusion directions (machine and transverse) increased with the VTES concentration increasing and even more with the addition of a small quantity of a peroxide. Some reductions of the tensile strength and elongation at break were observed, but these reductions were not considerable. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of Silane-Grafted and Moisture Crosslinked Low Density Polyethylene. Part II: Electrical,Thermal and Mechanical Properties

Among different polyethylene cross-linking methods, such as peroxide, irradiation, and silane cross-linking, silane-based methods are the most suitable methods for producing cable insulation and hot water pipe materials due to process simplicity and superior properties of its product. Some electrical, thermal and mechanical properties of silane-grafted water-cross-linked polyethylene were investigated. The effects of silane grafting and gel content on volume resistivity, tensile properties and melting behavior of low density polyethylene (LDPE) were studied. Results indicated that volume resistivity increased with increasing gel content. Stress at break increased with increasing grafting level and gel content. Elongation at break increased with grafting and decreased with gel content. High temperature tensile properties showed that cross-linked polyethylene (XLPE) is more stable than LDPE at high temperature. In differential scanning calorimetry (DSC) analysis a broad endothermic peak appeared for XLPE due to phase separation. Melting point and crystalline percentage decreased with increased grafting level and gel content. Incorporation of carbon black into XLPE reduced the volume resistivity and degree of crystallization.     

Thermal,mechanical, and dielectric behaviors of crosslinked linear low density polyethylene/polyolefin elastomers blends

Crosslinked linear low density polyethylene (XLPE) containing polyolefin elastomers (POE) has been evaluated. The blends with different dicumyl peroxide (DCP) and POE contents have been prepared and processed by compression molding. A series of the samples obtained have been investigated by gel content determination, scanning electron microscopy (SEM), different scanning calorimetry (DSC), mechanical, and dielectric behaviors measurements. The results obtained clearly show the relevant influence of the POE content, as well as of the DCP content, which tends to enhance crosslinking. As expected, the toughness of XLPE is improved by using adequate content of POE, and the blends exhibit a much more similar tensile behavior to that of elastomer. In addition, the results indicate that the blends possess the excellent dielectric behaviors, such as dielectric constant and dissipation factor. The crystallinity of the blends decreases as the DCP and POE contents increase. The melting temperature of the blends also decreases with the increase of DCP content, while POE content has few influences on the melting temperature of the blends. The SEM images strongly reveal that the blends are partially compatible, and the POE can be dispersed well in the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1920–1927, 2007     

Separation,size reduction,and processing of XLPE from electrical transmission and distribution cable

The recycling of power transmission cable insulated with crosslinked PE (XLPE) was investigated by using different methods of separation and reprocessing. Separation was attempted by thermo‐chemical, thermo‐mechanical and microwave‐mechanical means, the latter being the most successful. A mechanism encompassing all of these was formulated. Compression molding, extrusion, and injection molding with and without preheating of the material were also investigated. It was found that by preheating the XLPE and injection molding under high injection pressure, the neat XLPE could be formed into shapes with tensile strengths equal to that of the original insulation. In view of available observations, possible mechanisms for the flow and reconsolidation of XLPE crumb are proposed and discussed.     

Compatible thermoplastic starch/polyethylene blends by one‐step reactive extrusion

In the presence of dicumyl peroxide (DCP), the thermal plasticization of starch and its compatibilizing modification with polyethylene was accomplished by one‐step reactive extrusion in a single‐screw extruder at the same time. Because of the formation of polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) during the extrusion, it was used as the compatibilizer between the thermoplastic starch and polyethylene. The blending samples were characterized by means of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic thermal mechanical analysis (DTMA) and Fourier‐transform infrared (FTIR) analysis. The experimental results showed that in the presence of DCP the addition of MAH improved the mutual dispersion of molecules in thermoplastic starch and polyethylene. From TGA, we concluded that the thermal stability of the blends with MAH was improved compared with the blends without MAH. The DTMA and FTIR results indicated that, with the addition of MAH, the compatibility of molecules between thermoplastic starch and polyethylene in the blends was improved. Copyright © 2004 Society of Chemical Industry     

交联剂含量对交联聚乙烯滚塑制品冲击性能与结构的影响

制备了不同交联剂含量的交联聚乙烯(XLPE)材料及滚塑制品,比较了交联母料不同稀释比例下所得材料的流变特性、交联行为,研究了交联剂含量对样品力学性能(弯曲强度、缺口冲击强度)、不同温度时的落锤冲击强度以及厚度梯度方向的晶体尺寸、结晶度以及交联度等微观结构的影响。结果显示:随交联母料稀释比增大,交联反应略有延迟、交联反应程度降低,制品结晶度增加、缺口冲击强度降低、弯曲模量升高;交联母料稀释比在1:6~1:12时,测试温度25℃时样品落锤冲击强度均为25 J/mm以上,测试温度由25℃逐步下降至-40℃时,交联剂含量高的滚塑样品(M1-6)的落锤冲击强度可保持25 J/mm以上,稀释比例较大的滚塑样品出现韧性-脆性转变(-40℃落锤冲击为1 J/mm)。     

Benzoyl peroxide as a crosslinking agent for polyethylene

The efficiency of benzoyl peroxide (BPO) as a crosslinking agent for polyethylene (PE) was studied as a function of concentration and temperature in relation with the resin melt flow index and particle size. The investigation can lead to the selection of suitable materials and operating conditions for a proper crosslinking process. The decomposition characteristics of the initiator studied can be regulated in order to allow faster production rates when crosslinked PE are prepared by injection molding.     

Assessment of hindered phenol antioxidants on processing stability of peroxide‐cure LDPE by rheology and DSC analysis

Influence of commercial phenol antioxidants Irganox 300, 1010, 1035, and 1076 on peroxide‐cure reaction of low‐density polyethylene (LDPE) was evaluated through isothermal dynamic rheological and nonisothermal differential scanning calorimetry (DSC) testing. The results indicated that phenol antioxidants could reduce storage modulus of LDPE completely crosslinked at 175°C while they have a neglectable effect on gel fracture and activity energy of crosslinking reaction. On the other hand, time sweep dynamic rheological test revealed the antioxidants 1035 and 1076 with low molecular weight and low melting point could significantly depress scorch of crosslinkable LDPE at 135°C. The isothermal time sweep dynamic rheology test method was more sensitive than nonisothermal DSC test for characterizing the influence of phenol antioxidants on crosslinking kinetics of peroxide‐cure reaction of LDPE. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of polyethylene modified through phase‐transfer‐catalyzed graft copolymerization

In an effort to impart biodegradability, polyethylene (PE) was modified through the graft copolymerization of vinyl monomers such as acrylamide (AAm) and acrylic acid (AAc) by a phase‐transfer‐catalyst method. The grafting percentage of AAm and AAc for PE was found to be dependent on the dibenzoyl peroxide concentration, monomer concentration, time, temperature, and concentration of the phase‐transfer catalyst. Some AAm‐ and AAc‐grafted PE samples were prepared by chemical, UV, and γ‐radiation methods. The biodegradation of samples of PE, polyethylene‐g‐polyacrylamide, and polyethylene‐g‐poly(acrylic acid) prepared by all these methods was studied. The weight loss of the samples over a period of time was observed with soil‐burial tests. The grafted samples prepared by the phase‐transfer‐catalyst method showed better biodegradation results than those prepared by other methods of grafting. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study of some properties of waste LDPE/waste butyl rubber blends using different compatibilizing agents and gamma irradiation

Blends of waste low‐density polyethylene with waste butyl rubber of equal quantities containing reactive compatibilizing agents, namely: maliec anhydride; glycidyle methacrylate, divinyl benzene, tetraethyleneglycoldimethacrylate and diethyleneglycoldimethacrylate were preparedand exposed to different γ‐irradiation doses up to 400 kGy. The swelling behavior in organic solvent of the gel and soluble fractions and the degree of crosslinking were investigated. The mechanical properties, namely tensile strength and elongation at break were also studied. Thermal properties using thermo gravimetric analysis and differential scanning calorimetry analysis follow analyses have been followed up to follow the change of the structure for the irradiated and nonradiated blends. Results obtained indicated improvement in physical, mechanical and thermal properties on irradiation of the prepared blends which incorporate compatibilizing agents, but with varying degrees. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

过氧化物交联聚乙烯热收缩管成型研究

简要介绍了聚乙烯高能辐射交联、硅烷化学交联和过氧化物化学交联,给出了交联前后分子结构变化的示意图,说明3种交联方法所得到的交联聚乙烯分子结构十分接近,在性能上基本没有差别。采用最新的过氧化物交联配方,并给出详细的生产工艺,使用最新研制的具有自主知识产权的活塞式挤出机加工成型交联聚乙烯热收缩管坯,并用自制的扩管装置扩张成型热收缩管。针对试验结果,对产品的凝胶率、力学物理性能和电性能进行了讨论,并比较了辐射交联、硅烷交联和过氧化物交联3种交联生产工艺在设备投资成本、产品质量控制、能耗、交联反应时间、产品的实际交联度和产品的表面质量等方面的优劣。     

Effect of cellulose nanofibers and acetylated cellulose nanofibers on the properties of low‐density polyethylene/thermoplastic starch blends

The aim of this study was to evaluate the effect of cellulose nanofibers (CNFs) and acetylated cellulose nanofibers (ACNFs) on the properties of low‐density polyethylene/thermoplastic starch/polyethylene‐grafted maleic anhydride (LDPE/TPS/PE‐g‐MA) blends. For this purpose, CNFs, isolated from wheat straw fibers, were first acetylated using acetic anhydride in order to modify their hydrophilicity. Afterwards, LDPE/TPS/PE‐g‐MA blends were reinforced using either CNFs or ACNFs at various concentrations (1–5 wt%) with a twin‐screw extruder. The mechanical results demonstrated that addition of ACNFs more significantly improved the ultimate tensile strength and Young's modulus of blends than addition of CNFs, albeit elongation at break of both reinforced blends decreased compared with the neat sample. Additionally, biodegradability and water absorption capacity of blends improved due to the incorporation of both nanofibers, these effects being more pronounced for CNF‐assisted blends than ACNF‐reinforced counterparts. © 2018 Society of Chemical Industry