Moisture crosslinking process for foamed polymers, journal. The term curing refers to the crosslinking of thermosetting resins, such as unsaturated polyester and epoxy resin, and the term vulcanization is characteristically used for rubbers. For example, polyethylene will soften and flow, and lose critical physical properties at elevated temperatures, thereby limiting its applications. Apart from the crosslinking thereof, the radiation treatment of polyethylene in air results in a radiationinduced oxidation of the polymer rendering it with polar functional groups. Thermal and mechanical properties of vinyltrimethoxysilane.
Their mechanical, thermal and chemical properties were analyzed. This paper will focus on the silane crosslinking process. The aim of this study was the investigation of the use of modified talcum for supporting crosslinking and as novel nucleating agent for physical foaming of polyethylene. The uvinitiated crosslinking process of polyethylene molecules is fulfilled. The first significant industrial use of radiation processing was implemented in the late. C rosslinking of polyethylene is a subject of interest, having been emerged as a result of the need to meet application requirements which were not satisfied by the neat polyethylene itself. And yet, crosslinking the carbon atoms suffices to transform such material into a superior material that may be resistant to temperature, pressure, corrosion, and that can be used in a variety of applications. It is also ozone resistant and has many of the same properties as polyethylene foam but also has the ability to protect class a surfaces. Us3297641a us338311a us33831164a us3297641a us 3297641 a us3297641 a us 3297641a us 338311 a us338311 a us 338311a us 33831164 a us33831164 a us 33831164a us 3297641 a us3297641 a us 3297641a authority us united states prior art keywords polyethylene crosslinking polymer additive oxygen prior art date 19640117 legal status the legal status is an assumption and. The three most common methods of crosslinking polyethylene are as follows. Crosslinking definition of crosslinking by medical. Cross linking is a stabilization process in polymer chemistry which leads to multidimensional extension of polymeric chain resulting in network structure. Effect of polymer structure and additives on silane grafting.
Crosslinking is often an unwanted result of freeradical degradation processes. Preparation and characterization of ambienttemperature selfcrosslinkable watersoluble acrylic resin for pe film ink after decellularization of native articular cartilage figure 4d, the tissue was then. In the case of those compounds used as insulation and jacketing materials, they are called polymers. Efforts to decrease crosslinking extent of polyethylene in. Functional groups are introduced into the binder polymers to make self crosslinking systems, which are initiated by heating. To achieve high direct current dc dielectric performance of crosslinked polyethylene xlpe applied for insulated cable, the auxiliary crosslinking agent of trimethylolpropane trimethacrylate tmptma is employed in photoninitiated crosslinking process to the present polarmolecular group which will introduce deep traps for charge carriers.
Expired lifetime application number us810529a inventor ernest r gilmont. In the socalled engel process, a mixture of hdpe and 2% peroxide is at first mixed at low temperatures in an extruder and then crosslinked at high temperatures between 200 and 250 c. The silane crosslinking process involves at least two stages, which may be done together. The last radiationinduced effect in polyethylene that received little industrial attention, is the oxidation of the polymer when irradiated in air. Crosslinking agentsx crosslinking is the formation of chemical links between molecular chains to form a threedimensional network of connected molecules. Crosslinking of polyethylene for low wear using radiation and thermal treatments. Polyethylene crosslinking may be induced through three different methods.
During the xlpe manufacturing process, a catalyst peroxide is built into the resin, which creates a free radical. Crosslinking is effectively the formation of a lattice like structure. Crosslinking of polyethylene into pex for pipes results in improved. A consultants meeting on the controlling of degradation effects in radiation processing of polymers, held in 2002, provided an opportunity for. Crosslinked polyethylene polymer engineering engtips. Pdf polyethylene crosslinking by twostep silane method. The ultraviolet uv irradiation crosslinking reactions of polyethylene and the electronic properties of photoinitiators and reaction products are theoretically investigated by the firstprinciples calculations. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed. Brabender plasticorder studies of the process of crosslinking. All plastic materials consist of complex, very large molecules.
It requires doses generally comprised between 50 and 200 kgy, and involves single steps or short kinetic chain length reactions. Silane grafting and crosslinking of metallocenecatalysed. Polymer crystallinity 2 high density polyethylene is an example of a crystalline polymer. Based on crosslinking ofpolyethylene and other polymers pvc, pvdf, rubbers, acrylates, etc. A polymer is a large molecule built up by repetition of many, smaller chemical units. Us2916481a crosslinking of polyethylene with novel. A mechanism for the enhanced crosslinking of polyethylene. Moisture crosslinking process for foamed polymers moisture crosslinking process for foamed polymers pape, peter g. Uncrosslinked polyethylene has the melting point of 100c, however, after crosslinking no flow would be noticed even at 150c 1, 2, where elastic behaviour prevails. Eb process, crosslinking is induced by the interaction of highenergy electrons with the polymeric material.
The free radical generates the crosslinking of the polymer chain, so the tank essentially becomes one giant molecule. The technique, often called bioconjugation when referring to its use with proteins and other biomolecules, is an essential component of many proteomics methods, including creation of detectable probes for western blotting. C ross linking of polyethylene is a subject of interest, having been emerged as a result of the need to meet application requirements which were not satisfied by the neat polyethylene itself. Crosslinking of polyethylene for low wear using radiation. It is a physical process in which radicals trigger crosslinking reactions in the polymers. The most wellknown example of crosslinking is the vulcanisation of natural latex or butadiene polymers with sulphur, an accelerator and zinc oxide. Effects of the polyethylene glycol hydrogel crosslinking. Chemical crosslinking of polyethylene and its effect on water. Crosslinking of polyvinyl alcohol with tetrahydroxyborate ion.
Moisture crosslinking has many benefits over peroxide. However, the process of crosslinking reduces fracture toughness, raising concerns as to whether it can be safely used in total knee arthroplasty tka. Rem, voor een commissie aangewezen door het college voor promoties in het openbaar te verdedigen op. Crosslinking of recycled polyethylene by gamma and. Expired lifetime application number us338311a inventor frank x werber razmic.
Silane crosslinked polyethylene from different commercial. In the process of silane crosslinking, reactive groups are first grafted on pe molecules by addition of silane and very small amount of peroxide, whereafter shaping takes place in onestep monosil l, or twostep sioplas extrusion process. Crosslinking chemistry for highperformance polymer networks. Amorphous polyethylene is an elastomer a soft and pliable polymer which is rather useless on its own. Biopolymers include fibers such as cotton, wool, and spider silk, as well as proteins, polysaccharides, and dna in our bodies. The crosslinked polyethylene xlpe materials are prepared in. While many polymers are manmade synthetic, including polyethylene, teflon, kevlar, and nylon, many natural polymers, or biopolymers, also exist. In peroxide crosslinking, organic peroxide and polyethylene are blended during extrusion process and free radicals are formed, crosslinking the polymer chain to produce a network during thermal decomposition 9. Highdensity crosslinked polyethylene, or xlpe, is a thermoset resin that is specifically designed for critical applications like chemical storage. Peroxide crosslinking technology requires the temperature profile to be within a tight operating window during processing.
The crosslinking of polyethylene using peroxides e. The crosslinking process essentially forms bonds between the polymer chains, which could be directly between carbon to carbon or a. Crosslinking of oriented polyethylene by electron beam. However, the enhanced resistance to plastic deformation that benefits wear behavior comes at the expense of other mechanical properties. In the socalled lubonyl process polyethylene is crosslinked preadded azo compounds after extrusion in a hot salt bath. A mechanism for the enhanced crosslinking of polyethylene by the incorporation of acrylic acid d. Crosslinking process crosslinking is a process in which carbon atoms of same or different polyethylene chains are joined together to form the threedimensional network structure1416. It is the crystallization of polyethylene which yields its unique properties. Crosslinking of oriented polyethylene by electron bearn radiation. View enhanced pdf access article on wiley online library html view. Polymer crosslinking longchain branching ebeam services. Physical foaming and crosslinking of polyethylene with. Pdf controlling factors of degassing in crosslinked. Rheological behaviour of polyethylene with peroxide.
Highdensity crosslinked polyethylene xlpe poly processing. Polyethylene both low and highdensity forms of polyethylene are resistant to singledose radiation sterilization and can withstand, with out substantial change in mechanical properties, doses up to at least 100 mrad 23. The uv initiated crosslinking process of polyethylene molecules is fulfilled. These degradative changes may be accelerated by oxidative attack from the.
Properties of crosslinked ultrahighmolecularweight polyethylene gladius lewis department of mechanical engineering, the university of memphis, memphis, tn 381523180, usa abstract substantially reducing the rate of generation of wear particles at the surfaces of ultrahighmolecularweight polyethylene. Other crucial advantages of crosslinked polyethylene for pipes are. Crosslinked polyethylene, commonly abbreviated to pex or xlpe, is a form of polyethylene with crosslinks. Silane crosslinked polyethylene from different commercial pes. Silane crosslinking of high density polyethylene as catalyzed by. The technique, often called bioconjugation when referring to its use with proteins and other biomolecules, is an essential component of many proteomics methods, including creation of detectable probes for western blotting and elisa and strategies for investigating protein structure and interactions. Crosslinking of recycled polyethylene by gamma and electron. Irradiation crosslinking of recycling low density polyethylene by electron beam and gamma rays could be the solution to improve their properties. The spectrum of properties obtained depends on the basic polymer used. Under some conditions welldefined chainfolded crystals form. During the extrusion process, the initiator decomposes, and gas and radicals are formed. Chemical crosslinking of polyethylene and its effect on. Highly crosslinked polyethylene is safe for use in total.
Radiation crosslinking takes place at room temperature. Read brabender plasticorder studies of the process of crosslinking polyethylene, journal of applied polymer science on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. With the help of crosslinking agents, polyethylene in particular makes a remarkable transformation from commodity thermoplastic to useful engineering material. Effect of polymer structure and additives on silane. In peoples opinion, plastic is a light and weak substance that easily melts when warmed.
This makes it possible to use pex products in applica tions with higher temperature require ments that exceed the temperature stabil ity of normal thermoplastic grades. The crosslinking process essentially forms bonds between the polymer chains, which. The effect of zno on shelf life of silanegrafted polyethylene granules j. Controlling of degradation effects in radiation processing of. And yet, crosslinking the carbon atoms suffices to transform such material into a superior material. Radiation crosslinked ldpe o rings, an inexpensive substitute for ptfe and polysilicone gaskets in high temperature applications, are widely used in the industry. Chemistry of crosslinking thermo fisher scientific us. Crosslinked polyethylene an overview sciencedirect topics. Efforts to decrease crosslinking extent of polyethylene in a. A new method of cross linking of pe improves properties. The process involves meltgrafting of vinyl silane onto polymer chains and crosslinking of the grafted polymer. Crosslinked polyethylene, commonly abbreviated pex, xpe or xlpe, is a form of polyethylene with crosslinks. Through crosslinking, the thermodimen sional stability of polyethylene pex can be signi.
Silane crosslinking, catalyst, high density polyethylene, properties. Electron beam processing effectively and efficiently creates beneficial changes in material properties and performance with processes such as polymer crosslinking, longchain branching and chain scissioning. The process involves accelerating a beam of electrons to near light speed. Crosslinking of polymers is the largest commercial application of radiation processing. Box 14965115 2danish polymer centre, department of chemical engineering 3danish polymer centre, department of production and management. The grafting process was carried out in an internal mixer rheomix haake, sys 90, nj, usa with a. For the modification of the talcum, a thermal initiator was linked to the talcum surface. Properties of crosslinked ultrahighmolecularweight. In the process of silane crosslinking, reactive groups are first. Heat treatment of uhmwpe after irradiation is commonly. Mixing, extrusion and crosslinking the polymer is blended inline and extruded into solid sheet form. Crosslinked polyethylene finds wide applications in packaging and electrical insulation applications and rotomoulding.
Efforts to decrease crosslinking extent of polyethylene in a reactive extrusion grafting process. What makes polyethylene so useful is the fact that it can be polymerized in a specific way which allows the molecules to pack together and crystallize. But in medical, foam, pipe, wirecable, and other pe applications, only controlled crosslinking provides the higher physical properties that are needed. One of the main conclusions of the crp was that much remained to be learned in terms of understanding degradation mechanism and phenomena. Here, we analyze the degassing process of a byproduct methane formed during the peroxideinduced crosslinking of polyethylene. The process of crosslinking unfilled thermoplastic polyethylene has been followed with the aid of the brabender plasticorder.
Rheological behaviour of polyethylene with peroxide crosslinking agent ismaeil ghasemi1, peter szabo2, henrik koblitz rasmussen3 1iran polymer institute, tehran, iran, p. The crosslinking density was measured through a typical process. Chemical crosslinking of polyethylene and its effect on water tree initiation and propagation florin ciuprina elmat, faculty of electrical engineering, university politehnica of bucharest, splaiul independentei 3, 060042, bucharest, romania gisele teissedre, jean cesar filippini g2e laboratory cnrsinpgujf. Polyethylene in general crosslinks on irradiation, although there is a chain scission mechanism as well 5. Basically, radiation crosslinking takes place after the moulding process injection moulding. Free radicals are deleterious because they will react with available oxygen i. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, and insulation for high tension high voltage electrical cables. Different methods of crosslinking and effect of process parameters. It is shown that extrusion conditions without any significant scorching can be obtained with this instrument. Crosslinking is the process of chemically joining two or more molecules by a covalent bond. Highly crosslinked ultra highmolecularweight polyethylene has shown great promise as an orthopedic bearing in total hip replacements. The crosslinked polyethylene xlpe materials are prepared in experiments that employ the uvinitiated crosslinking technique with different photoninitiation systems. Crosslinking agents can be added during the produc. Heatshrinkproducts a uniqueness of radiation treatment.
This paper presents a comparison on the effects of gamma and electron irradiation on virgin and recycled polyethylene. Chemical crosslinking of polyethylene and its effect on water tree initiation and propagation florin ciuprina. Us2916481a us810529a us81052959a us2916481a us 2916481 a us2916481 a us 2916481a us 810529 a us810529 a us 810529a us 81052959 a us81052959 a us 81052959a us 2916481 a us2916481 a us 2916481a authority us united states prior art keywords polyethylene peroxide bis crosslinking weight prior art date 19590114 legal status the legal status is an assumption and is. Pdf properties of polyolefins can be modified by crosslinking process. Highdensity crosslinked polyethylene xlpe highdensity crosslinked polyethylene, or xlpe, is a thermoset resin that is specifically designed for critical applications like chemical storage. Radiation crosslinking of ldpe o rings, in the finished form was carried out at the 20 kw2 mev, ilu 6 type eb facility installed at the bhabha atomic research centre, bombay to establish irradiation technique for. Thermal and mechanical properties of vinyltrimethoxysilane vtmos crosslined high molecular weight 33 polyethylene hmwpe from our knowledge, there is a lack of studies regarding crosslinking of the polyethylene grade used in this study and the resulting mechanical properties. The vulcanization of rubber using elemental sulfur is an example of crosslinking, converting raw rubber from a weak plastic to a highly resilient elastomer. Crosslinking may assist in further improving the wear resistance of the uhmw pe.
In an embodiment, the crosslinking is initiated below the melting temperature of the uhmw pe. Crosslinking reagents contain reactive ends to specific functional groups primary amines, sulfhydryls, etc. For the manufacture of the polyethylene pipes used for potable water supplies, dynasylan vtmo is an ideal crosslinker. Cross linked polymer polymer crosslinking cross linking. A diffusion model based on ficks law is used to obtain the controlling factors of degassing in a crosslinked polyethylene xlpe insulated power cable. This sheet is then crosslinked, a process that enhances material strength, durability and temperature resistance. Study on the structure of peroxide crosslinked polyethylene. Moisture crosslinking process for foamed polymers wiley online. Highly crosslinked polyethylene xlpe has been used with good initial success in hip arthroplasty to reduce wear. In an embodiment, the crosslinking is initiated after compacting but before.
Crosslinked polyethylene foam is a closedcell foam characterized by a compact feel and resistance to water. In addition to the advantages associated with crosslinked polyethylene, it is also capable of absorbing high loadings of fillers compared to uncrosslinked. Radiation effects onpolymeric systems polyethylene crosslinking wire and cable insulation. Effect of polymer structure and additives on silane grafting of polyethylene j. Properties of polyolefins can be modified by crosslinking process. Lemstra department ofpolymer technology, eindhoven university of technology, po box 5,5600 mb eindhoven, the netherlands received 10november 1987 theinfluence ofdrawing on the. The present processes comprise crosslinking polyethylene or using crosslinked polyethylene. Although different hydrogel crosslinking mechanisms are known to result in distinct network structures, it is still unknown how these various mechanisms influence biomolecule release. Charlesby department of physics, royal military college of science, shrivenham, swindon, wiltshire received july 20, 1971 the e. Introduction crosslinked polyethylene, commonly abbreviated pex or xlpe, can be produced via three different crosslinking processes. In many countries, dynasylan vtmo has received a document of compliance issued silane crosslinking of polyethylenehd pipes.
Several studies about crosslinked polyolefines, especially polyethylene were carried for diverse authors 35. Upon cooling, secondary bonds tend to pull the molecules together into parallel bundles, not perfectly crystalline but not amorphous either. Here we compared the effects of chaingrowth and stepgrowth polymerization for hydrogel crosslinking on the efficiency of protein release and diffusivity. For some plastics, crosslinking activators are necessary. Experimental low density polyethylene ldpe, supplied by trocellen with 5% azodicarbonamide adca, as blowing agent. The manufacturing process comprises three essential stages. Crosslinking is the general term for the process of forming covalent bonds or relatively short sequences of chemical bonds to join two polymer chains together. Thermo scientific crosslinking technical handbook easy molecular bonding crosslinking technology. Conventional and crosslinked polyethylene properties. Free radicals are byproducts of radiation in the crosslinking process. Radiation effects onpolymeric systems polyethylene. Thereby, the crosslinking takes place primarily in the amorphous regions, while the crystallinity remains largely intact. And pexa pipes offered the greatest resis tance to creep at high temperature, crack propagation.