Blends of high‐density polyethylene with solid silicone additive

Silicone masterbatch (SMB) is a pelletized formulation containing 50% of an ultrahigh molecular‐weight polydimethylsiloxane dispersed in polyethylene. This SMB is designed to be used as an additive in polyethylene‐compatible systems to impart benefits such as processing improvement and modification of surface characteristics. In this work, binary blends of high‐density polyethylene (HDPE) and SMB were prepared by melt‐mixing technique to study the influence of this masterbatch on the processing and mechanical properties of HDPE. Ternary blends were also prepared by the addition of silane‐grafted polyethylene (HDPE‐VTES) as compatibilizer. The blends were analyzed by melting flow rate (MFR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile tests. Data of final torque and MFR showed that SMB improved the processability of pure HDPE. DSC results showed differences in crystalline behavior between binary and ternary blends. In the former, the degree of crystallinity increased up to 10 wt % of SMB content; beyond this concentration, it decreased. In ternary blends, a reverse behavior was observed. The morphologic study showed silicone particles uniformly distributed in HDPE matrix. With high SMB concentration, the addition of HDPE‐VTES significantly reduced the size of silicone particles. In the range of SMB composition studied, the mechanical properties of blends lower slightly compared to pure HDPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2347–2354, 2002     

作为添加剂的颗粒状有机硅树脂在热塑性塑料中的应用

描述了一种以超高分子量(uhmw)的聚二甲基硅氧烷(PDMS)为基料的新型、多功能固体有机硅添加剂，着重描述了这些新型颗粒状有机硅树脂作为添加剂应用于热塑性塑料挤出。通过实例说明了颗粒状有机硅树脂能非常有效地改善热塑性塑料的加工性和流动性，尤其适用于充填的聚烯烃混合物。此外，它们能进一步提高冲击强度和抗张强度等机械性能，并且对于改善表面光滑性和抗磨损性也十分有效。     

Preparation of poly(IPDI‐PTMO‐siloxanes) and influence of siloxane structure on reactivity and mechanical properties

Siloxane‐modified polyurethanes were prepared through isophorone diisocyanates (IPDI), poly(tetramethylene oxide) (PTMO), and siloxanes. IPDI served as the hard segment in the structure. Both PTMO and siloxanes were diols and served as the soft segments. In addition, different chemical structures of siloxanes were used, in which siloxane chains would remain in the main chain of polyurethanes (PU) or become the side chain of PU. First, the reactivities of PTMO and siloxanes to react with IPDI in bulk system were studied through DSC, in which the reaction heat was related to their reactivities. Copolymerization of IPDI, PTMO, and siloxanes in bulk were also studied. The results showed that hydrophobicity and steric hindrance of siloxane diols led to their low reactivities. Next, a series of siloxane‐modified PU in toluene solvent were synthesized, and the conversion of NCO groups was determined by the method of chemical titration. In the synthesis of PU copolymers in a solution polymerization, because of low reactivity of siloxanes, a two‐step procedure was adopted. The siloxane diol was first reacted with IPDI in toluene to form NCO‐terminated prepolymer. Then PTMO was added to form final PUcopolymers. The addition of side‐chain siloxanes resulted in PU copolymers with higher molecular weight than main‐chain siloxanes. Both main‐chain and side‐chain siloxanes increased the elongation at break and tensile strength of final PU copolymers. The microphase‐separation of siloxane segments was observed by SEM, which was the main cause for the improved mechanical properties. POLYM. ENG. SCI., 47:625–632, 2007. © 2007 Society of Plastics Engineers.     

A new class of silicone resins for coatings

A new class of silicone has been developed for coatings or as coating additives. Cycloaliphatic silane monomers were prepared and reacted into more easily handled cyclic oligomers. These cyclic oligomers were ring-opened into siloxane polymers. The polymers were functionalized with a variety of groups, including: amino, glycidyl epoxide, cyclohexene epoxide, acrylic, and alkoxysilane. The cycloaliphatic silicones have been designed for a number of different curing conditions: (1) ambient temperature-cure (amino and glycidyl epoxide), (2) cationic ultraviolet (UV)-cure (cyclohexene epoxide), (3) radical UV-cure (acrylic), and (4) moisture-cure (alkoxysilane). The end usages thus far have been focused on silicone coatings; however, usage as coating additives will be a focus for future research. The cycloaliphatic silicone has been UV-cured with mixed sol–gel precursors for usage as aerospace coatings. The cycloaliphatic silicones have also been ambient temperature-cured for release coatings, and have application as anti-fouling coatings. The inherent low surface energy makes the cycloaliphatic silicones prime candidates for surface tension additives. Presented at the 2006 FutureCoat! Conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1–3, 2006.     

Vinyl ester resin modified with silicone‐based additives: II. Flammability properties

Silicone‐based additives have been used as fire retardants for thermoplastics, presenting the advantages of improving processing and impact resistance of the polymers. In this work we used three different silicone‐based additives as modifiers of a thermoset based on a vinyl ester resin. The additives are fine powders made up of about 50 wt % ultra high molecular weight polydimethylsiloxane and 50 wt % silica. The differences between them are the functional groups inserted on the additives and the size and size distribution of the particles. The additives were dispersed in resin containing 35 wt % of styrene. For curing the mixture a conventional catalyst and initiator were used and the reaction was carried out in two ways, differing in the curing temperature, the post curing temperature, and the time, and in the addition of dimethylaniline (DMA) as a promoter of the polyaddition reaction. The samples were characterized by thermogravimetric analyses and swelling experiments. The fire retardances of the samples were evaluated by the determination of the flash‐ignition, self‐ignition, and pyrolysis temperatures (ASTM D1919–91a), and of the oxygen index (ASTM D‐2863–91). The results obtained showed that the silicone‐based additives and the methods used in the preparation of the modified resin influence the flash‐ignition, self‐ignition, and pyrolysis temperatures, but not the oxygen index. Samples cured by different methods present different network characteristics, which influence their thermal decomposition. The volatile species produced by thermal decomposition may be a combination of inert and active species. The network structure may influence only the inert fraction of the volatiles, not the combustibles. These volatile inert species (smoke‐black, water vapor, carbon dioxide, etc.) probably dilute the combustibles in the solid and in the gaseous phase, increasing the flash‐ignition temperature of the samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 644–649, 2006     

硅氧烷表面活性剂（V）（续4）：作为表面改性剂在聚合物中的应用

聚合物的表面性质在许多应用中起着关键性的作用，用最佳性能是在树脂应用时使整体／表面性质达到平衡。有许多方法可以对聚合材料进行表面改性，其中大多数方法是对终产物的表面进行处理。本中我们将阐述特定的含硅氧烷的共聚物，把它们作为表面改性添加剂加入到各种有机聚合物中，它们在加工过程中移到体系表面，从而使聚合物表面得到改性。虽然硅氧烷苯身是疏水性的，但是如果使用含有亲水链节的硅氧烷共聚物也可以得到亲水性的     

Solid‐state compaction and drawing of nascent reactor powders of ultra‐high‐molecular‐weight polyethylene

The continuous production of ultra‐high‐molecular‐weight polyethylene (UHMWPE) filaments was studied by the direct roll forming of nascent reactor powders followed by subsequent multistage orientation drawing below their melting points. The UHMWPE reactor powders used in this study were prepared by the polymerization of ethylene in the presence of soluble magnesium complexes, and they exhibited high yield even at low reaction temperatures. The unique, microporous powder morphology contributed to the successful compaction of the UHMWPE powders into coherent tapes below their melting temperatures. The small‐angle X‐ray scattering study of the compacted tapes revealed that folded‐chain crystals with a relatively long‐range order were formed during the compaction and were transformed into extended‐chain crystals as the draw ratio increased. Our results also reveal that the drawability and tensile and thermal properties of the filaments depended sensitively on both the polymerization and solid‐state processing conditions. The fiber drawn to a total draw ratio of 90 in the study had a tensile strength of 2.5 GPa and a tensile modulus of 130 GPa. Finally, the solid‐state drawn UHMWPE filaments were treated with O₂ plasma, and the enhancement of the interfacial shear strength by the surface treatment is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 718–730, 2005     

The role of silicone powders in reducing the heat release rate and evolution of smoke in flame retardant thermoplastics

New powdered silicone additives for plastics have been developed that give benefits in flame retardant formulations. Cone calorimeter evaluations of thermoplastics, with or without other flame retardant additives, show reduction in rates of heat release, smoke generation, and carbon monoxide evolution. Other benefits that have been observed are: improved processing, reduced torque, reduced build-up on screws, and increased impact strength. The effect of silicone powder additives on the combustion of several thermoplastics will be shown. A suggested mechanism is discussed.     

Mechanism study on surface activation of surfactant‐modified polyvinyl siloxane impression materials

This study examined the mechanism on the surface activation of hydrophilic polyvinyl siloxane impression materials incorporated with nonionic surfactants. Hydrophilic polyvinyl siloxane impression materials were prepared with a polydimethylsiloxane composition and nonionic surfactants. The surfactants used were nonylphenoxy poly(ethyleneoxy) ethanol homologs of varying ethyleneoxy chain length. These homologs were designated NP4, NP6, and NP10 according to the mole number of ethyleneoxy group (hydrophilic group) of 4, 6, and 10, respectively. The incorporation of a nonionic surfactant into polyvinyl siloxanes enhanced their hydrophilicity and consequently led to the significant reduction in the contact angles. The higher the concentration of surfactant that was incorporated, the lower the contact angles that were observed. The contact angle was lowest when NP4 was incorporated, even though NP4 is less hydrophilic than NP6 and NP10, which implies that the exposed surfactant concentration on the surface was highest when NP4 was used. Relatively lower surface energy of NP4 among three surfactants would induce spatial distribution of NP4 on the hydrophobic surface of polyvinyl siloxane and consequently resulted in higher surfactant concentration on the surface of the silicone impression material. The surfactant dispersion size also seemed to be relevant for the surface activation in these surfactant‐modified silicone impression materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2395–2401, 2004     

Ultraviolet‐induced degradation of Ziegler‐Natta and metallocene catalyzed polyethylenes

The metallocene revolution has aroused a storm of interest and associated questions regarding the performance and durability of polyolefins. This new technology has impacted the additives used to stabilize and process polymers. In this work, Ziegler‐Natta and metallocene polyethylene (PE) samples were exposed to natural weather conditions under high doses of ultraviolet radiation, high temperature, and increased humidity. Weather‐induced degradation of the two sets of PEs was studied using gel permeation chromatography, mechanical properties testing, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The gel permeation chromatography analysis indicated the change in molecular weight distribution and molecular weights of metallocene PE to be more stable than conventional Ziegler‐Natta PE. The tensile properties of metallocene PE are known to have higher values than Ziegler‐Natta PE. The former exhibited a lower drop rate in mechanical properties when exposed to natural weather. Formations of nonvolatile carbonyl oxidation products, which absorb in the infrared region with a maximum absorbance level at 1742 cm⁻¹ were determined. This indicated a higher rate of photo‐oxidative and thermal degradation of Ziegler‐Natta PE as compared with metallocene PE. The ultraviolet stabilization of metallocene PE may require different doses and a new kind of stabilizer system that can impart a longer useful lifetime and are cost effective for PE used for outdoor purposes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1591–1596, 2000     

Novel materials based on silicone–acrylate copolymer networks

This article presents a broad class of materials made by copolymerization of a family of telechelic free radically polymerizable siloxanes with various acrylate monomers that polymerize to form high T_g polymers. Films with properties ranging from strong elastomers to plastics have been obtained by UV‐initiated bulk copolymerization of functional siloxanes dissolved in acrylate monomers (in the presence of a photoinitiator). The molecular weight of the functional siloxanes, the nature of functional endgroups, the choice of (meth)acrylate comonomer, and the siloxane/acrylate ratio all have a rather dramatic effect on the morphology, and thus, on the properties of the copolymeric networks. Physical properties of the materials, such as optical appearance and mechanical and transport properties are correlated with the unique morphologies observed by TEM studies. Unusual properties such as reversible whitening of some of the materials and low Poisson ratios have been attributed to the microcavitation observed when high T_g acrylate domains interfere with the network deformation. Networks composed of high T_g acrylates (major fraction) coreacted with elastomeric siloxanes can provide heat‐shrinkable materials when they are elongated at temperatures higher than the T_g of the corresponding polyacrylates and quenched. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 159–180, 2001     

Effect of the incorporation of hydroxy‐terminated liquid silicones on the cure characteristics,morphology, and release of a model protein from silicone elastomer‐covered rods

Silicone elastomer systems have previously been shown to offer potential for the sustained release of protein therapeutics. However, the general requirement for the incorporation of large amounts of release enhancing solid excipients to achieve therapeutically effective release rates from these otherwise hydrophobic polymer systems can detrimentally affect the viscosity of the precure silicone elastomer mixture and its curing characteristics. The increase in viscosity necessitates the use of higher operating pressures in manufacture, resulting in higher shear stresses that are often detrimental to the structural integrity of the incorporated protein. The addition of liquid silicones increases the initial tan δ value and the tan δ values in the early stages of curing by increasing the liquid character (G″) of the silicone elastomer system and reducing its elastic character (G′), thereby reducing the shear stress placed on the formulation during manufacture and minimizing the potential for protein degradation. However, SEM analysis has demonstrated that if the liquid character of the silicone elastomer is too high, the formulation will be unable to fill the mold during manufacture. This study demonstrates that incorporation of liquid hydroxy‐terminated polydimethylsiloxanes into addition‐cure silicone elastomer‐covered rod formulations can both effectively lower the viscosity of the precured silicone elastomer and enhance the release rate of the model therapeutic protein bovine serum albumin. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Molecular weight and the Mark‐Houwink relation for ultra‐high molecular weight charged polyacrylamide determined using automatic batch mode multi‐angle light scattering

This study presents an automatic batch mode (i.e., off‐line) multi‐angle light scattering (MALS) method for the molecular weight (MW) determination of ultra‐high MW (UHMW) polyacrylamide (PAM) homopolymer and acrylamide copolymers. This method combines a MALS detector with a sample dilution and injection device that automatically delivers a concentration gradient from a stock solution. The automation makes it practical to use the batch MALS method for routine MW analysis of UHMW polymers. The automatic batch MALS analyses of a series of poly(sodium acrylate‐co‐acrylamide) (30:70 mol %) in 1.0M NaCl show a non‐linear Mark‐Houwink relation in the MW range of 1.2 × 10⁶ to 12.6 × 10⁶ g mol^?1. The entire molecular weight range can be fit with a quadratic relation or two linear equations, one for molecular weight up to 5.3 × 10⁶ g mol^?1 and the other from 5.3 × 10⁶ to 12.6 × 10⁶ g mol^?1. The non‐linear Mark‐Houwink relation suggests that the extrapolation of the Mark‐Houwink equation beyond the measured MW range into the UHMW regions can significantly overestimate the MW of the UHMW polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43748.     

Study on gel‐spinning process of ultra‐high molecular weight polyethylene

An ultra‐high molecular weight polyethylene (UHMW‐PE) fiber was prepared by gel spinning using general kerosene as the solvent and gasoline as the extraction solvent. The process of the phase separation of gel as‐spun, spun under various spinning conditions, was investigated. Its extracting and drying process were also studied. The results reveal that the gel as‐spun, spun under a lower spin draft and a lower spin quenching temperature, extracted in times and dried under free‐shrinkage, exhibits a good afterdrawability that eventually endows the fiber with excellent mechanical behaviors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 670–675, 1999     

Fire‐resistant elastomers

The molecular design of semi‐inorganic polymers has produced polysilphenylene–siloxane and polyphosphazene elastomers having comparable fire safety to heat resistant engineering plastics. In flaming combustion a polyphosphazene rubber had a four times lower peak heat release rate than the polyurethane elastomer currently used in fire‐blocked aircraft seat cushions. The addition of expandable graphite flakes to polyurethane and polyphosphazene elastomers reduces their peak heat release rates by factors of seven and five, respectively. Published in 2003 by John Wiley & Sons, Ltd.     

Synthesis and characterization of siloxane‐based cyanate ester elastomers from readily available materials: a top‐down approach

A number of siloxane‐based cyanate ester (SiCE) elastomers were prepared from commercially available starting reagents employing a hydrosilylation reaction. Each elastomer was designed to utilize 2,4,6‐tris(allyloxy)‐1,3,5‐triazine as a crosslinker and multifunctional vinyl component in the hydrosilylation reaction, ensuring that the triazine rings were completely formed, and thus the elastomers resemble fully cured cyanate ester networks. The hydride‐terminated siloxane components used were varied from small‐molecule siloxanes to pre‐polymers of different molecular weights. Attenuated total reflectance Fourier transform infrared analysis confirmed the successful hydrosilylation reaction and complete curing of the SiCE elastomers via functional group analysis. Thermal characterization by thermogravimetric analysis and differential scanning calorimetry demonstrated that thermal properties of the elastomers could be tailored depending on the type of siloxane component that was utilized. The gel content of the elastomers was also determined. Investigations into the effects of a platinum catalyst on the elastomers determined that the presence of the catalyst affected the thermochemical stability of the SiCE elastomers. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Silikon als Rohstoff für Schäumer und Entschäumer

Silicone as Raw Material for Foaming and Anti-Foaming Agents The remarkable significance of methyl polysiloxanes in the field of anti-foaming agents is based on two fundamental principles, namely, low intermolecular interactions (low surface tension), and the unique variability of the polymer system which permits that by variation of molecular weight, molecular weight distribution as well as the nature and number of end groups, these agents can be made to fit into a particular type of application. The above properties have also led to the use of modified methyl siloxanes as foam stabilizers. In the latter case, a further factor enhancing the efficacy by the introduction of a solubilizing group in the modified siloxane is made use of. Examples for the same are polyether modified methyl polysiloxanes as foam stabilizers in polyurethane foams, and anionactive methyl siloxanes containing sulfate groups as foaming agents in fire extinguishing systems.     

Injection and injection compression molding of ultra‐high‐molecular weight polyethylene powder

Ultra‐high‐molecular weight polyethylene (UHMWPE) powder was processed using injection molding (IM) with different cavity thicknesses and injection‐compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and avoid jeopardizing the UHMWPE molecular structure. Dynamic mechanical analysis (DMA) and Fourier‐transform infrared spectroscopy tests confirmed that the thermal and oxidative degradations of the material were avoided but crosslinking was induced during melt processing. Tensile tests and impact tests showed that the ICM samples were superior to those of IM. Increased cavity thickness and ICM were helpful for reducing the injection pressure and improving the mechanical properties due to effective packing of the material. Short shot molding showed that the UHMWPE melt did not exhibit the typical progressive and smooth melt front advancements. Due to its highly entangled polymer chains structure, it entered the cavity as an irregular porous‐like structure, as shown by short shots and micro‐computed tomography scans. A delamination skin layer (around 300‐μm thick and independent of cavity thickness) was formed on all IM sample surfaces while it was absent in the ICM samples, suggesting two different flow behaviors between IM and ICM during the packing phase. POLYM. ENG. SCI., 59:E170–E179, 2019. © 2018 Society of Plastics Engineers     

Degradation of biomedical polydimethylsiloxanes during exposure to in vivo biofilm environment monitored by FE‐SEM,ATR‐FTIR,and MALDI‐TOF MS

Polymers used for biomedical purposes in medical devices are usually requested to be inert to degradation. This article describes that slow irreversible changes were observed in silicone surfaces exposed to in vivo biofilms even if silicone, in general, is supposed to have excellent long‐term properties. Tracheostomy tubes made of silicone rubber were exposed to in vivo biofilm environments in clinical tests for periods of 1, 3, and 6 months. The chemical degradation was monitored by MALDI‐TOF MS, ATR‐FTIR, and FE‐SEM. In addition, the physical changes were monitored by contact angle and hardness measurements. Cyclic polydimethylsiloxane (PDMS) was detected on the surfaces of new (unaged) silicones. On the surfaces of the in vivo samples new compounds, presumably linear methyl‐hydroxyl‐terminated PDMS, were detected in addition to cyclic PDMS. These compounds may be formed as a result of the hydrolysis of linear dimethyl terminated PDMS, which is also present in the silicone rubber. ATR‐FTIR spectroscopy confirmed that hydrolysis had indeed occurred during the in vivo exposure, since Si? OH groups were detected. Furthermore, significant changes in the topography were detected by FE‐SEM, indicating the initiation of degradation. No significant changes in the contact angle of the in vivo used samples were observed, but this information may be shielded by the fact that biofilm may remain on the surface, despite the thorough cleaning before the analysis. It is also possible that the surface hydrophobicity was recovered by the diffusion of linear low‐molecular‐weight compounds from the bulk. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Radiation‐induced crosslinking of ultra high molecular weight polyethylene fibers by means of electron beams

Crosslinking of ultra high molecular weight polyethylene fibers (UHMW‐PE fibers) is investigated by means of electron beam irradiation. The structure and mechanical properties of the fibers in different irradiation atmospheres are discussed. The results show that the gel fraction and crosslinking density increase with the increase of absorbed dose. The swelling ratio and average molecular weight of crosslinked net decrease with the increase of absorbed dose. The relation between s + s^?1 of the UHMW‐PE fibers and reciprocal irradiation dose 1/R is obtained. The tensile strength and failure elongation decrease with the increase of absorbed dose, and the tensile modulus increases with the increase of absorbed dose. The samples are irradiated in air, vacuum, and acetylene atmospheres, separately. The radiation effects, such as crosslinking fraction and mechanical properties of UHMW‐PE fibers, are the most significant in acetylene atmosphere in comparison with in air and in vacuum. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1761–1764, 2005