Self- healing material - Wikipedia. Animation 1. 3. D measurement of Self- Healing material from Tosoh Corporation measured by Digital Holographic Microscopy. The surface has been scratched by a metallic tool. Animation 2. Section of self- healing material recovering from a scratch. Self- healing materials are artificial or synthetically- created substances that have the built- in ability to automatically repair damage to themselves without any external diagnosis of the problem or human intervention. Generally, materials will degrade over time due to fatigue, environmental conditions, or damage incurred during operation. Cracks and other types of damage on a microscopic level have been shown to change thermal, electrical, and acoustical properties of materials, and the propagation of cracks can lead to eventual failure of the material. In general, cracks are hard to detect at an early stage, and manual intervention is required for periodic inspections and repairs. In contrast, self- healing materials counter degradation through the initiation of a repair mechanism that responds to the micro- damage. About 6,0. 00 years ago, they used lime to plaster the pyramids at Giza. In addition, the Egyptians also incorporated various limes into their religious temples as well as their homes. Indian traditional structures built with lime mortar, which are more than 4,0. Mohanjo- Daro is still a heritage monument of Indian civilization. Such approaches are sometimes referred to as biomimetic. Healing mechanisms vary from an instrinsic repair of the material to the addition of a repair agent contained in a microscopic vessel. For a material to be strictly defined as autonomously self- healing, it is necessary that the healing process occurs without human intervention. Self- healing polymers may, however, activate in response to an external stimulus (light, temperature change, ..) to initiate the healing process. Polymers, Films, Elastomers, Fibers, and Coatings Polymer Fundamentals. Polymer consulting is a huge consultant practice area for CECON and our polymer experts span. ![]() Animations show the surface topography healing from a scratch made by a metallic tool. A material that can intrinsically correct damage caused by normal usage could prevent costs incurred by material failure and lower costs of a number of different industrial processes through longer part lifetime, and reduction of inefficiency caused by degradation over time. They used it to bind together decimenter- sized chunks of tuff, a aggregate of volcanic rock. Crystals of platey str. This ongoing crystal formation holds together the mortar and the coarse aggregate, countering crack formation and resulting in a material that has lasted for 1,9. The first international conference on self- healing materials was held in 2. In all plants and animals examined, firstly a self- sealing phase and secondly a self- healing phase can be identified. In plants, the rapid self- sealing prevents the plants from desiccation and from infection by pathogenic germs. This gives time for the subsequent self- healing of the injury which in addition to wound closure also results in the (partly) restoration of mechanical properties of the plant organ. Based on a variety of self- sealing and self- healing processes in plants different functional principles were successfully transferred into bio- inspired self- repairing materials. In cases where mainly physical- chemical processes are involved a transfer is especially promising. There is evidence in the academic literature. Deviation from Murray’s law is small however, increasing the diameter 1. Murray’s law is followed in some mechanical vessels, and using Murray’s law can reduce the hydraulic resistance throughout the vessels. Toohey et al. This showed partial recovery of toughness after fracture, and could be repeated several times because of the ability to replenish the channels after use. The process is not repeatable forever, because the polymer in the crack plane from previous healings would build up over time. This huge demand has forced to extend their reliability and maximum lifetime, and a new design class of polymeric materials that are able to restore their functionality after damage or fatigue was envisaged. These polymer materials can be divided into two different groups based on the approach to the self- healing mechanism: intrinsic or extrinsic. In the event of damage, the first response is triggering or actuation, which happens almost immediately after damage is sustained. The second response is transport of materials to the effected area, which also happens very quickly. The third response is the chemical repair process. ![]() Shore Durometer hardness testing of plastics is described, and conversion charts correlating various scales are presented. The Shore Duromter A and D scales of. Rubber Testing Rubber Process Analyzer 4 Moving Die Rheometer 8 Mooney Viscometer 10 Technology 12 sample Cutter 17 Automation 18 Density 20 Hardness 22. This process differs depending on the type of healing mechanism that is in place (e. These self- healing materials can be classified in three different ways: capsule based, vascular, and intrinsic. While similar in some ways, these three ways differ in the ways that response is hidden or prevented until actual damage is sustained. Polymer breakdown. IMR’s mechanical testing group offers accredited Nadcap and A2LA accredited tensile, hardness, fatigue, creep/stress rupture, more on metals, polymers and composites. Polymers have also been observed to undergo heterolytic bond cleavage through isotope labeling experiments. When a bond is cleaved heterolytically, cationic and. SPG also focuses on research, development, testing in the area of Solid Fuel Ramjets (SFRJ). EAG has significant expertise in polymer chemistry and offers a complete range of analyses for polymers, plasticsand composite - call us for a quote. Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape. ![]() The factors that determine how a polymer will yield include: type of stress, chemical properties inherent to the polymer, level and type of solvation, and temperature. When a bond is cleaved heterolytically, cationic and anionic species are formed which can in turn recombine to repair damage, can be quenched by solvent, or can react destructively with nearby polymers. This stress results in additional pi- bonded electrons as opposed to radical or charged moieties. Polymers And Rubbers Testing Blood![]() ![]() While extrinsic approaches are generally autonomous, intrinsic systems often require an external trigger for the healing to take place (such as thermo- mechanical, electrical, photo- stimuli, etc.). It is possible to distinguish among 5 main intrinsic self- healing strategies. The first one is based on reversible reactions, and the most widely used reaction scheme is based on Diels- Alder (DA) and retro- Diels- Alder (r. DA) reactions. A temperature trigger allows the redispertion of thermoplastic additives into cracks, giving rise to mechanical interlocking. The involved supramolecular interactions and ionomeric clusters are generally reversible and act as reversible cross- links, thus can equip polymers with self- healing ability. Since the polymer is stable under normal condition, the reversible process usually requires an external stimulus for it to occur. For a reversible healing polymer, if the material is damaged by means such as heating and reverted to its constituents, it can be repaired or . In general, the monomer containing the functional groups such as furan or maleimide form two carbon- carbon bonds in a specific manner and construct the polymer through DA reaction. This polymer, upon heating, breaks down to its original monomeric units via RDA reaction and then reforms the polymer upon cooling or through any other conditions that were initially used to make the polymer. During the last few decades, two types of reversible polymers have been studied: (i) polymers where the pendant groups, such as furan or maleimide groups, cross- link through successive DA coupling reactions; (ii) polymers where the multifunctional monomers link to each other through successive DA coupling reactions. For example, Saegusa et al. The reaction is shown in Scheme 3. They mixed the two complementary polymers to make a highly cross- linked material through DA reaction of furan and maleimide units at room temperature, as the cross- linkedpolymer is more thermodynamically stable than the individual starting materials. However, upon heating the polymer to 8. Cooling the two starting monomers, or damaged polymer, to room temperature for 7 days healed and reformed the polymer. The reversible DA/RDA reaction is not limited to furan- meleimides based polymers as it is shown by the work of Schiraldi et al. They have shown the reversible cross- linking of polymers bearing pendent anthracene group with maleimides. However, the reversible reaction occurred only partially upon heating to 2. For polymerization and healing processes of a DA- step- growth furan- maleimide based polymer (3. M4. F) were demonstrated by subjecting it to heating/cooling cycles. Tris- maleimide (3. M) and tetra- furan (4. F) formed a polymer through DA reaction and, when heated to 1. Subsequent heating to 9. Reversible highly cross- linked furan- maleimide based polymer network. Under reducing condition, the disulfide (SS) bridges in the polymer breaks and results in monomers, however, under oxidizing condition, the thiols (SH) of each monomer forms the disulfide bond, cross- linking the starting materials to form the polymer. Chujo et al. Reversible polymer cross- linking by disulfide bridges. This chemical reaction is naturally able to create covalent bonds at room temperature, allowing the polymer to autonomously heal without an external source of energy. Left to rest at room temperature, the material mended itself with 8. The material also include inexpensive commercially available compounds. The elastomer molecules were tweaked, making the bonds between them longer. The resulting molecules are easier to pull apart from one another and better able to rebond at room temperature with almost the same strength. The rebonding can be repeated. Stretchy, self- healing paints and other coatings recently took a step closer to common use, thanks to research being conducted at the University of Illinois. Scientists there have used . However, increase polymer length inhibits mobility and thereby impairs the ability for polymers to re- reversibly bond. Thus at each polymer length an optimal reversible bonding energy exists. While capsule- based polymers sequester the healing agents in little capsules that only release the agents if they are ruptured, vascular self- healing materials sequester the healing agent in capillary type hollow channels which can be interconnected one dimensionally, two dimensionally, or three dimensionally. After one of these capillaries is damaged, the network can be refilled by an outside source or another channel that was not damaged. Melt Index Testing of Polymers – Measuring Mass Flow Rate (MFR) and other Polymer Properties by Tinius Olsen. Using Tinius Olsen equipment it is possible to perform such tests on raw materials such as metals, polymers, textiles, rubbers, adhesives, food as well finished components. A whole series of tests are available including. They fall into the broad categories of: Melt- Flow Index Testing. Among the first instruments plastics molders, extruders, and compounders are likely to consider when outfitting a new lab is a melt- flow indexer or “melt indexer.” Known as an extrusion plastometer in more technical jargon, this apparatus has long been used to determine the melt- flow rate or mass- flow rate (MFR) of virgin and compounded thermoplastic resins. With the increased pressure on plastics processors to comply with quality standards for quality management, more of them are using these instruments to evaluate incoming material and test finished products. The melt- flow test detailed in the ASTM D1. ISO 1. 13. 3 standards quickly measures one point on the viscosity curve under standard conditions. While the relative simplicity of this test has remained the same, melt indexers have evolved considerably since they appeared in the 1. A specified load (weight) is applied to the piston, and the melted polymer is extruded through a capillary die of specific dimensions. Figure 1. Tinius Olsen's model MP6. Procedure A configuration. Properties Determined by Melt Flow Indexers. The mass of resin, in grams, that is extruded in 1. MFR, expressed in units of g/1. In contrast, long chains of high molecular weight and more complex structure yield greater flow resistance or viscosity. The Relationship of Mass Flow Rate to other Properties. The MFR, then, is an indicator of average molecular weight and is inversely related to it. A resin with an MFR of 5. MFR of 1. 0 g/1. 0 min. While a higher MFR material may be easier to process, physical properties related to molecular weight, such as impact resistance, are often lower. Figure 2. Cross section of melt indexer furnace. Mass Flow Rate or MFR and Quality Control. Thus, MFR is commonly used as a material- acceptance specification by processors and also as a means of comparing resins from different vendors. It also has many uses in quality control. Not only can variations in polymerization and compounding affect MFR of incoming resin, but it is also a valuable indicator of resin degradation caused by transport or storage conditions or improper drying. Regular MFR testing after molding or extrusion can help pinpoint improper processing conditions. It also provides a simple indicator of how addition of in- plant regrind or post- consumer reclaim may affect the virgin resin’s processability and end- use performance. Case Study – Using MFR for Quality Control. As an example of an actual case of how this information can be used: An injection molded polycarbonate part was found to crack when dropped. The virgin resin had an MFR of 2. A sample from a known “good” lot of parts was ground up and tested in a melt indexer. But a “problem” part showed an MFR of 9. From this evidence, it was discovered that the “bad” lot contained a large amount of regrind that had been thermally degraded in processing. ASTM 1. 23. 8 vs ISO 1. ASTM 1. 23. 8 and the ISO 1. The way the test is run is different, as are some technical specifications, which can lead to different results. Test Procedure ABoth ASTM 1. ISO 1. 13. 3 offer two variations of the standard melt- flow test: Procedure A and Procedure B. Procedure A describes a basic manual melt indexer. The “cuts” are weighed on an analytical balance to determine the average mass and this value is extrapolated to the mass that would be extruded in 1. MFR. Figure 3. Tinius Olsen model MP6. Procedure B configuration. Figure 4. Screenshot of equipment set- up screen from EP6. Melt Index Test Load Ranges. Test loads range from 1. The load and temperature to be used are determined by the material and the test method. Automated Cutters on Melt Indexers. All new melt indexers today are provided with automatic timers, and some have automatic extrudate cutters. Although the latter work well with some plastics, some resin melts are sticky or difficult to manipulate to obtain a clean cut and in many cases, automatic cutters cannot match the human hand. Calculating MFR Using Test Procedure BProcedure B testing is simpler in that there is no extrudate cutting or weighing because it is volumetric. The volume of the resin extruded is obtained from the geometry of the barrel and distance of piston travel over a measured time period. This determines the melt volume rate (MVR) in cc/1. From this value and the resin’s known melt density, the MFR can be calculated automatically. With Procedure B testing, the operator simply loads the barrel with resin, starts the test, and the instrument calculates the results. Advantages of Test Procedure BThis is the first advantage over basic Procedure A instruments; these units measure 2. The second advantage is that there is less user interference. Results, then, are generally more accurate and more reproducible. On the other hand, Procedure B testing requires an accurate value for the resin melt density at the test temperature. Such values are available in published literature- for example, typical values for “generic” PE and PP are cited in the ASTM 1. However, most sources consider it more accurate to measure the actual melt density of the specific resin being tested. This is done by combining elements of Procedure A and Procedure B in a single test run so as to obtain data for both weight and volume- hence, density. Today’s melt indexers for Procedure B can be used to perform both tests. Test Procedure A vs Procedure BThere is no general consensus as to which procedure is best. Some recommend Procedure A for most processors since it tests the . Others view Procedure A as best for operators that use a broad range of materials and additive packages whereas they see Procedure B as best suited to labs that make frequent measurements of the same type of material with a known melt density. Figure 5. Screenshot from EP6. SPC capabilities. Multi- Weight Melt Flow Test. There is also a multi- weight melt flow test, which unlike standard Method A and Method B, provides more than one measurement on a single charge under two or three different load conditions (using different weights). The multi- weight test is referenced under ASTM D1. Multi- Weight Melt Flow Test Instruments. Several suppliers offer multi- weight capability. In an instrument that can calculate shear rate and viscosity in addition to MFR, multi- weight measurement provides the equivalent of a “poor man’s capillary rheometer,” suppliers say. Most suppliers agree that multi- weight instruments are mainly suitable for use by resin producers or compounders who want to provide their customers with more information on how a material will behave. Features of Melt Flow Indexers. Price differences reflect mainly options. Temperature controls may include an automatic preheat phase as either standard or optional. Digital encoders are available to measure piston travel for Procedure B with much higher precision than the older optical technology using photocells or mechanical switches. Motorized lifting and lowering the weight onto the piston is another option. Other new options include automatic compaction of the resin pellets before heating. Manually tamping down the material with a rod can account for as much as 1. MFR results, and this variation is reportedly eliminated by a motor driven rod. Modular Design of Melt Flow Indexers. Some suppliers take a modular or building- block approach, which permits adding capabilities to a basic unit after purchase. For example, the initial purchase of a rudimentary Procedure A machine and the subsequent additions of an encoder switch, motorized weight lifting device, cleaning and purging accessories and pc based software, means that this rudimentary machine can be converted into a semi- automatic system that operates at the click of a single mouse click. Melt Indexer Ovens. Besides option packages, price differences among melt indexers also have to do with the way the units are manufactured and calibrated. While technical specs are prescribed by ASTM, some suppliers just meet them, while others exceed them. A key point when buying a melt indexer is that temperature control must be absolutely stable. For example, some units have two heating elements around the barrel, while others only have one. A bigger oven around the barrel will allow temperature to stabilize more quickly. Figure 6. Model MP6. Procedure B configuration with a motorised weight lowering platform for semi- automatic operation. Calibration of Melt Indexers. Suppliers also say calibration is critical to proper use of a melt indexer, and they recommend that buyers make sure their vendor offers calibration services. Calibration requires checking the temperature inside the barrel at a specific point above the die, and also confirming the dimensions of the barrel, piston, and die. The Importance of Cleaning Melt Flow Indexers. Finally, the die, piston, and barrel must be easily cleanable. Model MP6. 00 shown with lowered weight platform and pneumatic purge and pneumatic cleaning pistons for simplified rapid testing and cleaning.
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