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Material Starting 3. Protect



  • Material Starting 3. Protect
  • Chapter 18: Organic Synthesis
  • Introduction
  • the APIC 3rd Party Audit Task Force on behalf of the Active Pharmaceutical Ingredient Auditing of registered starting material (RSM) suppliers is a primary activity Instructions for the protection of clean equipment from contamination prior. The production of quality starting materials must be carefully planned in order to practices (GMP) guidelines published by WHO2 or under development3. the dosage form and the starting materials and are often intended to protect them. Control of starting materials and intermediate, bulk and finished products manufacture or environmental protection: these are normally governed by national.

    Material Starting 3. Protect

    The risk assessment tool was applied to starting materials for processes with recent submissions for which significant health authority queries had been received and to some development projects where the starting materials were identified as high risk during internal project review.

    These queries correlated well with high overall risk scores as illustrated by the following examples. Demonstration of the Risk Assessment Tool: To demonstrate the risk assessment tool the synthesis scheme for Vemurafenib shown in Figure 1 Patent submitted in 9 was assessed.

    The results are shown in Table 2. In this demonstration no starting materials were identified as high risk by the risk assessment tool primarily and the starting materials were globally accepted health authorities. In the example shown in Table 3 Starting Material 3 was identified as high risk by health authorities. In example shown in Table 4 both starting materials were identified as high risk by health authorities. In the example shown in Table 5 Starting Material 3 was identified as high risk during internal project review.

    In the example shown in Table 6 Starting Material 1 and 3 were identified as high risk during internal project review. While final starting material strategies in the Market Application are built up and justified based on the principles outlined in ICH Q11, the tool demonstrated to be valuable for teams to recognize risks early, focus process development resources and develop appropriate risk mitigation strategies.

    The output of the tool is never considered in isolation. It is merely a starting point to level-set expectations which is particularly helpful in large organizations to ensure consistent assumptions. The new risk assessment tool is a simple algorithm which can help identify potential health authority concerns. On the one hand, automation has the advantage of letting the operator carefully control collection volumes, track inventory and patient data, and minimize sample handling.

    On the other hand, automated instruments are generally costlier, and may require specially trained and experienced operators. Not all clinics or pharmaceutical manufacturers can afford the most complex equipment or data platforms.

    Since different variables can play into the quality and quantity of cells that can be collected, standardization of both leukapheresis instrumentation and operator training across cell therapy starting material collection sites is important.

    In a best-case scenario, apheresis nurses will be highly trained and experienced, with excellent venipuncture skills and a good bedside manner to put donors at ease. Optimizing and standardizing equipment and training helps protect and enable the highest quality, consistency and potency of the downstream clinical product. The goal of any cell therapy collection method is to optimize the number of healthy therapeutic cells present in the starting material.

    This often means that collection protocols must reach an optimal balance of yield and purity. Various enrichment techniques may be incorporated into the collection protocol itself, so specific methods should be worked out in advance to obtain optimal results. During post-collection processing, the number of target cells in a particular leukapheresis unit will inevitably decrease with each step in the manufacturing process, as cells are lost to handling methods and environmental stress.

    Quality control criteria for leukapheresis units should set pre-determined values for acceptable collection volumes, cell counts, purity, and cell viability. The tools and technology already exist, we just need to develop more thoughtful and standardized characterization assays to ensure a potent product.

    Once the leukapheresis unit is collected, the therapeutic potency of the cells must be protected until the unit can reach the processing facility. In practical terms, this often means leukapheresis products are cryopreserved prior to their use. Cryopreservation can improve stability while reducing or alleviating highly coordinated logistics challenges. Robust, data validated cryopreservation methods and media will optimize cell viability and functionality.

    Quality control assays should be performed both prior to shipping and upon arrival to ensure that product integrity has been maintained. Apheresis derived starting material will increasingly impact the practice of medicine, as cell-based therapies are validated and approved for the clinic. Using best practices when determining instrumentation and collection methods will ensure that these important therapies are given their best start.

    Article Stem cells were first discovered in human cord blood in How Genomics is Shaping Advanced Therapeutics Article Genomics technologies are guiding the development of advanced therapy medicinal products, i. Women in Science eBook eBook Read more. The drivers are lower costs and technical improvements, which allow the synthetics to emulate desirable natural fiber aesthetics while exhibiting superior in-use performance.

    The commodity markets are divided primarily among nylon, polyester, and polyolefin, with polyester emerging as the largest. Cost-performance and environmental considerations have led to a diminution in the use of cellulosics and acrylics. This same time period has seen the rapid growth of high-performance fiber technologies. These technologies fall into three classes:. High-modulus, high-strength fibers based on rodlike, liquid crystalline nematogenic polymers.

    The most common examples are the lyotropic aramids and the thermotropic polyesters. These fibers are characterized by tensile moduli greater than 70 gigapascals GPa , tensile strengths on the order of 3 to 4 GPa, and low properties in compression or shear. Morphological manipulation of conventional polymers, such as high-molecular-weight. Polymeric precursor fibers that can be converted to other chemical forms after spinning. The most common examples are acrylic fibers that can be converted to carbon fibers and a variety of silicon-containing polymeric fibers that can be converted to silicon carbide or silicon nitride fibers.

    Typical applications of high-performance fibers are composite reinforcement, ropes and cables, and antiballistic clothing. As a group, these fibers represent successful technical developments, but they have proved less commercially attractive than once believed for a variety of reasons.

    The spinning process can be described as follows. A polymer is first converted to a liquid through melting or dissolution, and the liquid is then continuously forced through a spinnerette a plate with many of small holes to form filaments. Most polymeric fibers are semicrystalline. If the polymer forms a stable melt, the process is called melt spinning.

    For polymers that degrade prior to melting, the polymer is spun from a solution; if the solvent is evaporated, the process is termed dry spinning; if the solution is coagulated in a nonsolvent bath, the process is termed wet spinning.

    Removal of the spinnerette from the wet spinning coagulation bath is the innovation known as dry-jet wet spinning. The ratio of final filament velocity to the initial filament velocity is termed the drawdown ratio. The principal parameters controlling the as-spun structure and, hence, properties of the as-spun filament are the rate of cooling and the applied stress. Crystallinity once formed can be further oriented by stretching and perfected through annealing. Key structural elements are the amount and orientation of crystalline regions, the orientation of noncrystalline regions, and connectivity between regions, tie molecules, and so on.

    Careful control of the sequence in which chains are oriented and crystallized has a profound effect on the microstructure produced. Such controlled processing allows, for example, the decoupling of crystalline and noncrystalline orientation, enabling fibers with high tensile modulus correlated with high crystalline orientation and low thermal shrinkage correlated with low noncrystalline orientation to be produced.

    Typical spinning speeds are thousands of meters per minute, typical melt drawdowns are on the order of , and typical solid-state draw ratios range from about 2 to 6 in conventional processing to greater than 50 in the production of certain high-performance products.

    High-performance fiber processing is characterized by maximizing axial chain orientation and minimizing. To control friction and static behavior in subsequent processing, a variety of oils or other surface treatments are applied to the fibers prior to take-up.

    The many complex processing steps of fibers add to the stress-temperature history of the fiber and hence significantly modify the end-use properties of the material. To a large extent, the conditions employed in spinning, in addition to the particular chemistry of the polymer being spun, determine the end-use performance of a fiber.

    Work on future fibers will focus on producing cost-performance improvements and product variants through morphological control rather than new chemistries. With the huge lengths of fibers produced, process robustness and property uniformity have always been major issues; future products will make more use of advanced computerized process control and will operate in areas of property response that are less sensitive to minor process variation.

    Elimination of downstream process steps will lead to additional cost-performance improvements, for example, on-line texturing and surface modifications to meet specific friction or adhesion requirements. Environmental considerations will influence future fiber developments in a number of areas. The elimination of solvent-based processing will be driven by stricter emissions standards, as will the elimination of heavy metal catalysis. Novel processes based on very fast melting techniques e.

    The reduction of off-specification production will become more important as the cost of waste disposal increases and as easy-to-reclaim fibers grow in importance e. The future of high-performance fibers lies in the reduction of costs and the improvement of utilization. The former is best influenced by lower-cost monomers, and the latter through the development of manufacturing technologies that allow cost-effective part production from fiber-reinforced composites.

    High-performance fiber development will cease to be solely performance driven and will, as in the case of all other fibers, become driven by cost and performance. Silks, produced by worms and spiders, have attracted attention because they possess tensile properties similar to those of high-performance synthetic fibers but with much higher toughness. The use of recombinant DNA techniques allows silks of specific molecular architectures to be produced and their performance to be correlated with specific chemical and physical features.

    The increased structure-property insights gained from these studies should allow the definition of biomimetic fibers, based on other than naturally occurring amino acids, with greatly improved performance characteristics. An adhesive is a material that, by means of surface attachment, can hold together solid materials. Adhesives have been used for most of recorded history. They are mentioned in Egyptian hieroglyphics, in the Bible, and in the writings of the early natural philosophers.

    The physical strength of an assembly made by the use of adhesives, known as an adhesive joint, is due partly to the forces of adhesion, but primarily to the cohesive strength of the polymeric materials used to formulate the adhesive. Thus, the range of strengths available in adhesive joints is limited to the strengths of the polymers useful in the formulation of adhesives.

    Indeed, the technology of adhesives tracks well with the technology of polymers. As new polymers were synthesized, new adhesives were developed that used those polymers.

    Adhesives are typically classified by their use or application. Thus structural adhesives are those materials used to join engineering materials such as metals, wood, and composites. Usually, it is expected that an adhesive joint made with a structural adhesive is capable of sustaining a stress load of 1, psi 6. Hot melt adhesives are those adhesives that are applied from the melt and whose properties are attained when the adhesive solidifies.

    Pressure-sensitive adhesives provide adherence and strength with only finger pressure during application. Adhesive tapes are manufactured by applying a pressure-sensitive adhesive to a backing.

    Rubber-based adhesives are, as the name implies, based on elastomers and are usually applied as a mastic or spray applied from solvent or water. Pressure-sensitive adhesives can be considered to be a subset of rubber-based adhesives.

    The ease of application of pressure-sensitive adhesives is superior to all other types of adhesives except possibly hot melt adhesives. Responsivity to finger pressure alone forming a bond is a desirable property, and pressure-sensitive adhesives of sufficient strength to perform structural tasks have been developed recently. One of the major uses of these double-coated foam tapes is to fasten most of the exterior and interior decorative and semistructural materials to the body of an automobile.

    The use of these foam tapes allows faster assembly and eliminates mechanical fasteners, which are a source of corrosion. Each of the major classes of adhesives described above can be further classified by its chemistry. Thus, the majority of structural adhesives are based on one or more of the following chemistries: The majority of hot melt adhesives are based on one or more of the following chemistries: Rubber-based adhesives are, for the most part, formulated using neoprene, nitrile, and natural rubbers.

    Pressure-sensitive adhesives are based on natural rubber, vinyl ethers, acrylics, silicones, and isoprene-styrene block co-polymers. Many paper-binding adhesives are based on dextrin or other. Adhesives have several advantages over other joining technologies. In general, adhesives have a lower density than mechanical fasteners, and so weight savings can be realized.

    Polymer-based adhesives have viscoelastic character and are thus capable of energy absorption. The energy absorption manifests itself in the form of dampening of vibrations and in the increase of fatigue resistance of a joint. Adhesives can be used to join electrochemically dissimilar materials and provide a corrosion-resistant joint.

    Adhesive joining is limited by the fact that an engineering database is unavailable for most adhesive materials. The strength and durability of an adhesive bond are subject to the nature of the surfaces to be joined. Part of the reason industrial adhesives have been so successful is that methods have been found to clean and treat surfaces to form good bonds. A better understanding of proper surface preparation for adhesives is needed. The major limitations to the broader use of adhesives in industry are the extreme sensitivity of adhesive bonding to surface conditions and the lack of a nondestructive quality control method.

    Adhesive technology can be solidly advanced by the synthesis of new monomers and polymers that extend the range of applicability of adhesive bonding. Thus, new materials should allow adhesives to be more flexible at cryogenic temperatures, more oxidation resistant at high temperatures, stronger at elevated temperatures, and more tolerant of an ill-prepared or low-surface-energy adherent.

    The engineering aspects of adhesive technology can be solidly advanced by including adhesive technology in university engineering courses and establishing an engineering database. In addition, an easy, nondestructive method of predicting the strength of a joint would be a major advance in the applicability of adhesives. Two drivers of advances in adhesive technology in the near future are economics and the environment.

    To be environmentally acceptable, new adhesive formulations should contain a minimum of solvent and in some applications should be biodegradable. To be economically attractive, adhesives should be easy to use and should provide a value-added feature to the customer that outweighs the disadvantages cited above. The time scale for introducing totally new polymers is increasing because the simplest monomers and the processes for converting them into polymers have already been identified and introduced into the marketplace.

    Furthermore, with increasing regulatory obstacles and the high cost of research, the economic stakes for introducing generically new polymers based on previously unknown chemistry and manufacturing processes have been raised considerably. Because this field was initially dominated by the ready opportunities for chemical innovation, serious development based on the more physical approach of alloying or.

    Now, the area of polymer blends is one of the routes to new materials that is most actively pursued by the polymer industry. There are several driving forces for blending two or more existing polymers. Quite often, the goal is to achieve a material having a combination of the properties unique to each of the components, such as chemical resistance and toughness. Another issue is cost reduction; a high-performance material can be blended with a lower-cost polymer to expand market opportunities.

    A third driving force for blending polymers of different types is addition of elastomeric materials to rigid and brittle polymers for the purpose of toughening. Such blends were the first commercial example of polymer blend technology and, even today, probably account for the largest volume of manufacturing of multicomponent polymer systems.

    The main problem is that frequently when polymers are blended, many critical properties are severely depressed because of incompatibility. On the other hand, some blends yield more or less additive property responses, and others display certain levels of synergism.

    The problem is knowing how to predict in advance which will occur and how to remedy deficiencies. From a fundamental point of view, one of the most interesting questions to ask about a blend of two polymers is whether they form a miscible mixture or solution.

    The thermodynamics of polymer blends is quite different from that of mixtures of low-molecular-weight materials, owing to their molecular size and the greater importance of compressibility effects. Because of these, miscibility of two polymers generally is driven by energetic rather than the usual entropy considerations that cause most low-molecular-weight materials to be soluble in one another.

    The simple theories predict that miscibility of blends is unlikely; however, recent research has shown that by carefully selecting or designing the component polymers there are many exceptions to this forecast. The phase diagram for polymer blends is often opposite of what is found for solutions of low-molecular-weight compounds.

    Polymers often phase separate on heating rather than on cooling as expected for compounds of low molecular weight. Theories to explain the behavior of miscible polymer blends have emerged, but theoretical guidance for predicting the responsible interactions is primitive.

    With the advent of modern computing power and software development, molecular mechanics calculations of this type are being attempted. Neutron scattering has provided considerable insight about the thermodynamic behavior of blends and the processes of phase separation. One of the earliest blend products was a miscible mixture of poly phenylene oxide and polystyrene.

    The former is relatively expensive and rather difficult to process. The addition of polystyrene lowers the cost and makes processing easier.

    Numerous other commercial products are now based on miscible or partially miscible polymer pairs, including polycarbonate-polyester blends and high-performance ABS materials. Frequently, the unfavorable polymer-polymer interactions that lead to immiscibility cause an unstable and uncontrolled morphology and a weak interface. These features translate into poor mechanical properties and low-value products, that is, incompatibility. When this is the case, strategies for achieving compatibility are sought, generally employing block or graft copolymers to be located at the interface, much like surfactants.

    These copolymers can be formed separately and added to the blend or formed in situ by reactive coupling at the interface during processing. The former route has, for example, made it possible to make blends of polyethylene and polystyrene useful for certain packaging applications by addition of block copolymers formed via anionic synthesis.

    However, viable synthetic routes to block copolymers needed for most commercially interesting combinations of polymer pairs are not available. For this reason, the route of reactive compatibilization is especially attractive and is receiving a great deal of attention for development of commercial products. It involves forming block or graft copolymers in situ during melt processing by reaction of functional groups.

    Extensive opportunities exist for developing schemes for compatibilization and for fundamental understanding of their mechanisms.

    A better understanding of polymer-polymer interactions and interfaces e. Especially important is the development of experimental techniques and better theories for exploring the physics of block and graft copolymers at such interfaces. This knowledge must be integrated with a better understanding of the rheology and processing of multiphase polymeric materials so that the morphology and interfacial behavior of these materials can be controlled.

    A wide variety of compatibilized polymer alloys have been commercialized, and the area is experiencing a high rate of growth. A product based on poly phenylene oxide , a polyamide, and an elastomer has been introduced for use in forming injection-molded automobile fenders and is currently being placed on several models of U. The polyamide confers toughness and chemical resistance, the poly phenylene oxide contributes resistance to the harsh thermal environment of automotive paint ovens, while the elastomer provides toughening.

    Another automotive application is the formation of plastic bumpers by injection molding of ternary blends of polycarbonate, poly butylene terephthalate , and a core shell emulsion-made elastomeric impact modifier Figure 3.

    In this blend, the polycarbonate brings toughness, which is augmented at low temperatures by the impact modifier, while the poly butylene terephthalate brings the needed chemical resistance to survive contact with gasoline, oils, and greases.

    In the first example, the poly phenylene oxide and polyamide are very incompatible, and reactive coupling of the phases is required for morphology control and for interfacial strengthening. In the second example, the polycarbonate and polyester apparently interact well enough that no compatibilizer is needed. They are chosen for their class-A surface, dimensional stability, impact strength, and corrosion and chemical resistance. The side claddings on these vehicles are molded of a resin that is a polyester-polycarbonate alloy, chosen for its cold temperature impact strength, chemical resistance, and quality surface.

    More than 60 pounds of engineering thermoplastics can be found on many of the vehicles. Toughening by the addition of rubber was first practiced for commodity polymers, such as polystyrene, poly vinyl chloride , polypropylene, and poly methyl methacrylate PMMA.

    Widely different processes and product designs were required to achieve optimal products. Now this approach is being applied to engineering thermoplastics and thermosets in order to move these materials into applications that require stringent mechanical performance under demanding conditions.

    This ensures an excellent growth opportunity for a variety of toughening agents. Elastomers with low glass transition temperatures are needed to impart toughness at low use temperatures, while thermal and oxidative. In addition, these elastomers must be dispersed within the matrix to an appropriate morphology or size scale and adequately coupled to the matrix. These two issues are often interrelated and specific to the particular matrix material. Continued efforts will be required to produce a better understanding of the various toughening mechanisms that are applicable to engineering polymers.

    Numerous opportunities exist to achieve better understanding that would shorten the time to develop new blends and alloys. There is an interesting parallel between this field and alloying in metallurgy, and the polymer community may be able to learn from the long experience of metallurgists. Both fields involve a broad spectrum of issues including synthesis, processing, physical structure, interfaces, fracture mechanics, and lifetime prediction.

    The United States is currently in a position of technical leadership; however, companies and universities around the world are also aggressively pursuing research and development in this field. Polymer composites can provide the greatest strength-to-weight and stiffness-to-weight ratios available in any material, even the lightest, strongest metals. Hence, high-performance and fuel-economy-driven applications are prime uses of such composites.

    One of the most important attributes is the opportunity to design various critical properties to suit the intended application. Indeed, performance may be controlled by altering the constituents, their geometries and arrangement, and the interfaces between them in the composite systems. This makes it possible to "create" materials tailored to applications, the single greatest advantage and future promise of these material systems.

    Structural composites are of interest in aerospace applications and in numerous industrial and consumer uses in which light weight, high strength, long fatigue life, and enhanced corrosion resistance are critical.

    Much needs to be done to advance processibility and durability, to provide a more comprehensive database, and to improve the economics of these systems. A wide range of future needs encompasses synthesis, characterization, processing, testing, and modeling of important polymer matrix composite systems. In general, the future of polymer matrix composites is bright. The engineering community is now in the second generation of applications of composites, and primary structures are now being designed with these materials.

    There is a growing confidence in the reliability and durability of polymer composites and a growing realization that they hold the promise of economic as well as engineering gain. Commercial programs such as high-speed civil transport will not succeed without the use of polymer composites. Integrated synthesis, processing, characterization, and modeling will allow the use of molecular concepts for the. A more precise understanding of the manufacturing, processing, and component design steps will greatly accelerate the acceptance of these advanced materials.

    New horizons for properties and performance, for example, in smart and intelligent materials, actuators, sensors, high-temperature organic materials, and multicomponent hybrid systems, will involve the potential of introducing a new age of economic success and technical excellence.

    Advanced polymer matrix composites have been used for more than 20 years, for example, on the B-1 bomber and for many top-of-the-line Navy and Air Force jet fighters. For military purposes, the high performance and stealthiness of composites have often outweighed issues of durability and even safety. Building lighter, more maneuverable tanks, trucks, and armored vehicles might be an area for future military growth.

    However, as the Pentagon's budget shrinks, efforts to transform these materials into civilian uses are under way Pasztor, Problems include the need to identify significant nondefense companies that will use advanced composites. For nearly 30 years, it has been suggested that aircraft designers around the world would rapidly utilize these new materials.

    Unfortunately, those predictions have not been realized, and U. For a number of reasons, there is continued reticence to employ these advanced materials in many areas, particularly in commercial aviation. Costs, processibility, and durability appear to be the major issues. To this point, this area has been considered a technical success but not a financial success. Nevertheless, aircraft in various stages of development have composites as some fraction of their structural weight.

    For example, 15 percent of the Boeing , 6 percent of the MD Trijet, and 15 percent of the MD are estimated to be composites. European aviation firms have begun flight-testing an all-composite tail rotor for a helicopter, and Japanese efforts are under way to develop a military helicopter that has a very high composite content.

    It has been predicted that in the future, fiber-reinforced composites FRCs will partially replace conventional materials in civil engineering applications. These could include buildings, bridges, sewage and water treatment facilities, marine structures, parking garages, and many other examples of infrastructure components.

    Composite materials are also expected to help replace conventional materials such as steel and concrete in many future projects. The polymer matrix resin composites discussed above have already made inroads in areas such as antenna coverage and water treatment plants. Sheet molding compounds, which are used extensively in automobiles and housing, are not considered by many structural engineers to be suitable for infrastructure replacement owing to their relatively low strength.

    Advanced polymer composites, on the other hand, which often consist of continuously reinforced fiber materials, have superior strength and stiffness. The liquid crystalline nature of stiff polymer molecules in solution was predicted by Onsager in , further refined by Flory in , and experimentally verified through aramid investigations at the Du Pont Company in the s.

    Flory suggested that as the molecular chain becomes more rodlike, a critical aspect ratio is reached, above which the molecules necessarily line up to pack efficiently in three dimensions. Liquid crystal polymer concepts have been extended to encompass a vast number of homopolymer and copolymer compositions that exhibit either lyotropic or thermotropic behavior. Industrially, most of the effort has been focused on the main-chain nematic polymers.

    These polymers combine inherently high thermal and mechanical properties with processing ease and versatility. Processing ease originates from the facile way that molecular rods can slide by one another, the very high mechanical properties come from the "extended chain" morphology present in the solid state, and the thermal stability derives from the highly aromatic chain chemistry.

    Inherent in this structure is a high level of structural, and hence property, anisotropy for example, the axial modulus is 1 to 2 orders of magnitude higher than the transverse modulus. The direction of molecular chain orientation is coincident with the direction of covalent bonding in the chain; normal to the orientation direction the bonding is secondary van der Waals, hydrogen bonding, and so on.

    Low orientation in these materials means global but not local randomness, and properties within "domains" are highly anisotropic. A useful spin-off of the study of liquid crystal polymers was the recognition of the importance of mesophases in the development of structure in conventional polymers.

    Examples of this include the stiffening of polyimide backbones to reduce the expansion coefficient and improve processibility and the recognition of the importance of a pseudo-hexagonal rotator, transient nematic phase in the crystallization of oriented polymer melts.

    Increasing the end-to-end distance of conventional polymers through the application of either mechanical or electromagnetic fields can lead to the formation of structure equivalent to that achieved by the manipulation of molecularly stiff molecules. Fibers from lyotropic para-aramid polymers Figure 3. The fibers are dry-jet wet spun from percent sulfuric acid solution with sufficient. An annealing step may be performed to improve structural perfection, resulting in an increase of fiber modulus.

    These fibers have very high modulus and tensile strengths as well as excellent thermal and environmental stability. Weaknesses include low compressive properties endemic with all highly uniaxially oriented polymers and a significant moisture regain. Worldwide fiber production capacity is about 70 million pounds Selling prices vary according to grade i. Consumption worldwide in was about 50 million pounds, somewhat trailing capacity. Major markets include reinforcement for rubber and composites, protective apparel, ropes and cable, and asbestos replacement.

    The use of para-aramid fiber is projected to grow at greater than 10 percent per year worldwide over the next 5 years. The environmental issues involved in the handling and disposal of large quantities of sulfuric acid or other solvents may make thermotropic approaches more attractive in the future.

    During the s, thermotropic copolyesters were commercialized world-wide. More versatile than the lyotropic polymers, these nematic copolyesters Figure 3. While fiber products exist, most of the commercial thermotropic copolyester is sold as glass-or mineral-filled molding resins, the majority into electrical and electronic markets. As in the case of the aramids, thermal and environmental stability is excellent.

    Advantages of these molding resins are the extremely low viscosity, allowing the filling of complex, thin-walled molds, excellent mold reproduction because of the low change in volume between liquid and solid, and fast cycle times. Weaknesses include property anisotropy and high cost. The future growth of the main-chain nematogenic polymers will be dominated by two factors:. Processing technology allowing cost-effective exploitation of properties, including orientation control in finished parts, as well as new forms e.

    Two particularly intriguing properties of nematogenic polymers not yet important commercially are ductility under cryogenic conditions and very low permeabilities of small molecules through the solid-state structure high barrier properties. A potentially attractive route to both lower price and improved property control is the blending of liquid crystal polymers with conventional polymers.

    An extensive literature exists, and interesting concepts such as self-reinforcing composites and molecular composites have been developed to describe immiscible and miscible liquid crystal polymer-containing blends. Major problems encountered in this technology include:. Inherent immiscibility of mesogenic and conventional polymers, leading to large-scale phase separation;. Strong dependence of blend morphology properties on processing and polymer variables; and.

    To date, commercial success for such blends has proved elusive. A related approach is the use of liquid crystal polymers in conventional composites, either as reinforcing fiber, matrix, or both.

    Penetration into conventional composite markets has been slow, the major problems being poor adhesion, poor compression fibers , and the lack of design criteria for composite parts where both matrix and ply are anisotropic. The potential of polymeric liquid crystals in device rather than structural applications has been recognized in both industry and academia, but no commercially viable products have yet emerged. The combination of inherent order, environmental stability, and ease of processing has led to interest in the use of polymeric liquid crystalline textures in applications as diverse as nonlinear optics, optical data storage, and "orienting carriers" for conducting polymers.

    With structural parameters of secondary importance, all textures are under active investigation. Both main-chain and side-chain approaches are of interest, the goal. Emerging problems include achieving sufficient density of active species to produce materials with competitive figures of merit i. Clearly, the introduction of mesogenicity into polymers opens vast possibilities for molecular design, which may ultimately lead to the creation of materials with highly specific and unique property sets.

    Polymers are used in many applications in which their main function is to regulate the migration of small molecules or ions from one region to another. Examples include containers whose walls must keep oxygen outside or carbon dioxide and water inside; coatings that protect substrates from water, oxygen, and salts; packaging films to protect foodstuffs from contamination, oxidation, or dehydration; so-called "smart packages," which allow vegetables to respire by balancing both oxygen and carbon dioxide transmission so that they remain fresh for long storage or shipping times; thin films for controlled delivery of drugs, fertilizers, herbicides, and so on; and ultrathin membranes for separation of fluid mixtures.

    These diverse functions can be achieved partly because the permeability to small molecules via a solution-diffusion mechanism can be varied over enormous ranges by manipulation of the molecular and physical structure of the polymer. The polymer that has the lowest known permeability to gases is bonedry poly vinyl alcohol , while the recently discovered poly trimethylsilyl propyne is the most permeable polymer known to date.

    The span between these limits for oxygen gas is a factor of 10 A variety of factors, including free volume, intermolecular forces, chain stiffness, and mobility, act together to cause this enormous range of transport behavior. Recent experimental work has provided a great deal of insight, while attempts to simulate the diffusional process using molecular mechanics are at a very primitive stage.

    There is clearly a need for guidance in molecular design of polymers for each of the types of applications described in more detail below. In addition, innovations in processing are needed. As shown earlier, packaging applications currently consume roughly one-third of the production of thermoplastic polymers for fabrication of a wide array of rigid and flexible package designs see Figure 3.

    These packages must have a variety of attributes, but one of the most important is to keep contaminants, especially oxygen, out, while critical contents such as carbon dioxide, flavors, and moisture are kept inside. Metals and glass are usually almost perfect barriers, whereas polymers always have a finite permeability, which can limit.

    In spite of this deficiency, the light weight, low cost, ease of fabrication, toughness, and clarity of polymers have driven producers to convert from metal and glass to polymeric packaging. Polymers often provide considerable savings in raw materials, fabrication, and transportation, as well as improved safety for the consumer relative to glass; however, these advantages must be weighed against complex life-cycle issues now being addressed.

    The following discussion illustrates the current state of this technology, its problems, and future opportunities. There are certain polymer molecular structures that provide good barrier properties; however, these structural features seem invariably to lead to other problems. For example, the polar structures of poly vinyl alcohol , polyacrylonitrile, and poly vinylidene chloride make these materials extremely good barriers to oxygen or carbon dioxide under certain conditions, but each material is very difficult to melt fabricate for the same reason.

    The good barrier properties stem from the strong interchain forces caused by polarity that make diffusional jumps of penetrant molecules very difficult. To overcome these same forces by heating, so that the polymer chains can move in relation to one another in a melt, requires temperatures that cause these reactive materials to degrade chemically by various mechanisms.

    Chapter 18: Organic Synthesis

    Records of Raw Materials, Intermediates, API Labelling and Packaging Materials. manufacture, nor aspects of protection of the environment. . 3. Reviewing all production batch records and ensuring that these are completed and signed. 3. Quality Assurance. 4. Personnel and Education. 5. Buildings and Facilities quality of starting materials of herbal origin requires an adequate quality . Buildings must provide adequate protection for the harvested medicinal plants/ herbal. To protect patients from potential unknown impurities introduced prior to The high risk score of Starting Material 3 correlates with the health.




    Records of Raw Materials, Intermediates, API Labelling and Packaging Materials. manufacture, nor aspects of protection of the environment. . 3. Reviewing all production batch records and ensuring that these are completed and signed.


    3. Quality Assurance. 4. Personnel and Education. 5. Buildings and Facilities quality of starting materials of herbal origin requires an adequate quality . Buildings must provide adequate protection for the harvested medicinal plants/ herbal.

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