Sealant is a substance used to block the passage of fluids through the surface or joints or openings in materials, a type of mechanical seal. In building construction sealant is sometimes synonymous with caulking and serve the purposes of blocking dust and heat transmission. Sealants may be flexible or rigid, permanent or temporary. Sealants are not adhesives but some have adhesive qualities and are called adhesive-sealants or structural sealants. Sealants were first used in prehistory in the broadest sense as mud and reeds to seal dwellings from the weather such as the daub in wattle and daub and thatching. Natural sealants and adhesive-sealants included plant resins such as pine pitch and birch pitch, wax, natural gum, clay mortar, lime mortar, lead and egg. In the 17th century glazing putty was first used to seal window glass made with linseed oil and chalk other drying oils were used to make oil-based putties which were referred to as caulks. In the 1920s polymers such as acrylic polymers, butyl polymers and silicone polymers were first developed and used in sealants.
By the 1960s synthetic-polymer-based sealants were available. Sealants, despite not having great strength, convey a number of properties, they seal top structures to the substrate, are effective in waterproofing processes by keeping moisture out the components in which they are used. They can provide thermal and acoustical insulation, may serve as fire barriers, they may have electrical properties, as well. Sealants can be used for simple smoothing or filling, they are called upon to perform several of these functions at once. A caulking sealant has three basic functions: It fills a gap between two or more substrates; the sealant performs these functions by way of correct formulation to achieve specific application and performance properties. Other than adhesives, there are few functional alternatives to the sealing process. Soldering or welding can be used as alternatives in certain instances, depending on the substrates and the relative movement that the substrates will see in service. However, the simplicity and reliability offered by organic elastomers make them the clear choice for performing these functions.
A sealant may be viscous material that has little or no flow characteristics and which stay where they are applied. Anaerobic acrylic sealants are the most desirable, as they are required to cure in the absence of air, unlike surface sealants that require air as part of the cure mechanism that changes state to become solid, once applied, is used to prevent the penetration of air, noise, fire, smoke, or liquid from one location through a barrier into another. Sealants are used to close small openings that are difficult to shut with other materials, such as concrete, etc. Desirable properties of sealants include insolubility, corrosion resistance, adhesion. Uses of sealants vary and sealants are used in many industries, for example, construction and aerospace industries. Sealants can be categorized in accordance with varying criteria, e. g. in accordance with the reactivity of the product in the ready-to-use condition or on the basis of its mechanical behavior after installation. The intended use or the chemical basis is used to classify sealants, too.
A typical classification system for most used sealants is shown below. Types of sealants fall between the higher-strength, adhesive-derived sealers and coatings at one end, low-strength putties and caulks at the other. Putties and caulks serve only one function -- i.e. to fill voids. Silicone is an example of a sealant - and has a proven long life and is unaffected by UV or extremes of weather or temperature. See below for other common types of sealants - The main difference between adhesives and sealants is that sealants have lower strength and higher elongation than adhesives do; when sealants are used between substrates having different thermal coefficients of expansion or differing elongation under stress, they need to have adequate flexibility and elongation. Sealants contain inert filler material and are formulated with an elastomer to give the required flexibility and elongation, they have a paste consistency to allow filling of gaps between substrates. Low shrinkage after application is required.
Many adhesive technologies can be formulated into sealants
The Sealers' War in southern New Zealand known as the "War of the Shirt", was a series of indiscriminate attacks and reprisals between Māori and European sealers. Minor misunderstandings between the two peoples lead to armed conflict; this resulted in a period of mistrust and animosity between Māori and sealers fueling several conflicts, leading to the deaths of about 74 people and the burning of the village of Otakou on the Otago Peninsula. Records exist from both sides of the conflict but not from any impartial observers. Late in 1810, Sydney Cove, an English sealing vessel, was anchored in Otago Harbour while its crew were working at Cape Saunders on the Otago Peninsula. Māori were in the habit of visiting such vessels to trade for pork and potatoes. During one such visit, a Māori chief, Te Wareripirau, according to one of Creed's informants, or Te Wahia, according to the other, stole a red shirt and a knife amongst other items; some of the sailors attacked the chief with cutlasses. He "fled from them with his bowels protruding through the wound in the side" and died.
"The Europeans fled, by ship & boats to the Molyneux" – the modern Clutha River mouth – where they attacked and killed another chief, Te Pahi. They left behind James Caddell. At Waipapa Point one of Sydney Cove's gangs landed and proceeded overland to the Mataura River mouth, where they were surprised and killed by Māori under Honegai; the Sydney Cove paused at Stewart Island before continuing its voyage. In a separate but related incident that same year men from Brothers, in the vicinity of Otago Harbour, proceeded south seeking a passing ship to take them back to Sydney. During this time four of them were killed by Māori; these tensions still existed in 1814 when six lascars from Matilda, absconded from her in a long boat near Fiordland. Near Dusky Sound three of them were killed and the other three were taken prisoner. Matilda went on to Stewart Island and from there sent Robert Brown in an open boat to look for the missing men, he came up the east coast and touched at Cape Saunders before going on up the coast to a point some eight miles north of Moeraki.
There he and his seven companions hauled the boat ashore and went to sleep under it, but were seen by Māori and attacked and all but two were killed. The two survivors fled through the night to what is now known as Bobby's Head near the Pleasant Valley. Māori entertained the survivors, but upon discussion with arriving Māori who had participated in the attack, killed the two survivors as well. Meanwhile, Fowler brought Matilda into the site of the 1810 incident. Here they received a friendly reception from the Māori and Fowler used this to attempt a correction of the common conception that the Māori were hostile to Europeans. In 1815 William Tucker, in the Otago Harbour area as early as 1809, landed again and settled at Whareakeake. There he kept goats and sheep, had a Māori wife, built a house, set up an export trade in ornamental hei-tiki – jade neck pendants made from old adzes, he left but returned on Sophia, a Hobart sealer commanded by James Kelly with other Europeans meaning to settle.
Sophia anchored in Otago Harbour in 1817 and Tucker was well-received. Two or three days Kelly went to visit Whareakeake in an open boat, with Tucker and five others, having been persuaded by Tucker not to take their firearms. At Whareakeake they had a friendly reception and encountered one of the Matilda's lascars who told them of his countrymen's fate, it seems Tucker had gone into his house but Kelly was attacked, at the instigation of the Whareakeake chief Te Matahaere. In the ensuing melee Veto Viole, John Griffiths, William Tucker were killed. Escaping by longboat, Kelly returned to Sophia in Otago Harbour, but suspected that the Māori there were planning an attack, he therefore attacked the Māori first, and over the next few days, he killed several people including Korako, destroyed multiple canoes and set fire to the village of Ōtākou. These hostilities and the diminution of seal populations, saw a decline in sealing ventures to southern New Zealand, it seems this was unknown to Captain Abimeleck Riggs of the American sealer General Gates, who in late 1819 landed a gang at Stewart Island.
He had a troubled cruise and it wasn't until 1821 that he returned. He dropped a second gang and a third at Chalky Inlet. Māori attacked the second gang in October 1821. Six of his men were captured, taken north up the west coast, where four were killed. Meanwhile, the Māori killed a boy; the Māori pursued the rest of the gang and killed two members before the survivors came across Captain Edwardson of Snapper in Chalky Inlet. The pursuing Māori were led by'Te Pehi','Topi' and'Te Whera'. With the pursuers was James Caddell, was captured from Sydney Cove, had acculturated himself to Māori society. Edwardson now took Caddell to Sydney, where his arrival caused a sensation in 1823 and where a peace was brokered. Thereafter, sealing resumed although it soon petered out again because the animal populations had been depleted. Behold the Moon: the European Occupation of the Dunedin District 1770–1848, Peter Entwhistle, Port Daniel Press, Dunedin, 1998. Taka, a Vignette Life of William Tucker 1784–1817, Peter Entwhistle, Port Daniel Press, Dunedin, 2005
Stone sealing is the application of a surface treatment to products constructed of natural stone to retard staining and corrosion. All bulk natural stone is riddled with interconnected capillary channels that permit penetration by liquids and gases; this is true for igneous rock types such as granite and basalt, metamorphic rocks such as marble and slate, sedimentary rocks such as limestone and sandstone. These porous channels act like a sponge, capillary action draws in liquids over time, along with any dissolved salts and other solutes. Porous stone, such as sandstone absorb liquids quickly, while denser igneous stones such as granite are less porous. Natural stone is used in kitchens, walls, dining rooms, around swimming pools, building foyers, public areas and facades. Since ancient times, stone has been popular for building and decorative purposes, it has been valued for its strength and insulation properties. It can be cut, cleft, or sculpted to shape as required, the variety of natural stone types and colors provide an exceptionally versatile range of building materials.
The porosity and makeup of most stone does, leave it prone to certain types of damage if unsealed. Staining is the most common form of damage, it is the result of oils or other liquids penetrate into the capillary channels and deposit material, impossible to remove without destroying the stone. Salt Attack occurs; the two commonest effects are spalling. Salts that expand on crystallization in capillary gaps can cause surface spalling. For example, various magnesium and calcium salts in sea water expand on drying by taking on water of crystallization; however sodium chloride, which does not include water of crystallization, can exert considerable expansive forces as its crystals grow. Efflorescence is the formation of a gritty deposit white, on the surface. Efflorescence is the result of mineral solutions in the capillary channels being drawn to the surface. If the water evaporates, the minerals remain as the so-called efflorescence, it can be the result of chemical reaction. In the open air the lime reacts with carbon dioxide to form water-insoluble calcium carbonate that might take the form of powdery efflorescence or dripstone-like crusting.
Acid Attack. Acid-soluble stone materials such as the calcite in marble and travertine, as well as the internal cement that binds the resistant grains in sandstone, react with acidic solutions on contact, or on absorbing acid-forming gases in polluted air, such as oxides of sulfur or nitrogen. Acid erodes the stone. In time it may cause deep pitting totally obliterating the forms of statues and other sculptures. Mild household acids, including cola, vinegar, lemon juice and milk, can damage vulnerable types of stone; the milder the acid, the longer it takes to etch calcite-based stone. Picture Framing occurs when water or grout moves into the edges of the stone to create an unsightly darkening or "frame" affect; such harm is irreversible. Freeze-thaw Spalling results; the general term is Frost weathering. The water expands on freezing, causing the stone to spall, crumble, or to crack through; the longevity and usefulness of stone can be extended by sealing its surface so as to exclude harmful liquids and gases.
The ancient Romans used olive oil to seal their stone. Such treatment provides some protection by excluding water and other weathering agents, but it stains the stone permanently. During the renaissance Europeans experimented with the use of topical varnishes and sealants made from ingredients such as egg white, natural resins and silica, which were clear, could be applied wet and harden to form a protective skin. Most such measures did not last long, some proved harmful in the long run. Modern stone sealers are divided into 3 broad types: Topical sealers Generally made from polyurethanes, acrylics, or natural wax; these sealers may be effective at stopping stains but, being exposed on the surface of the material, they tend to wear out quickly on high-traffic areas of flooring. This type of sealer will change the look and slip resistance of the surface when it is wet; these sealers are not breathable i.e. do not allow the escape of water vapour and other gases, are not effective against salt attack, such as efflorescence and spalling.
Penetrating sealers The most penetrating sealers use siliconates, fluoro-polymers and siloxanes, which repel liquids. These sealers penetrate the surface of the stone enough to anchor the material to the surface, they are longer lasting than topical sealers and do not alter the look of the stone, but still can change the slip characteristics of the surface and do wear quickly. Penetrating sealers require the use of special cleaners which both clean and top up the repellent ingredient left on the stone surface; these sealers are breathable to a certain degree, but do not penetrate enough to be effective against salt attack, such as efflorescence and spalling. Impregnating sealers Uses modified silanes; these are a type of penetrating sealer, which penetrate into the material, impregnating it with molecules which bond to
A heat sealer is a machine used to seal products and other thermoplastic materials using heat. This can be with uniform thermoplastic monolayers or with materials having several layers, at least one being thermoplastic. Heat sealing can join two similar materials together or can join dissimilar materials, one of which has a thermoplastic layer. Heat sealing is the process of sealing one thermoplastic to another similar thermoplastic using heat and pressure; the direct contact method of heat sealing utilizes a heated die or sealing bar to apply heat to a specific contact area or path to seal or weld the thermoplastics together. Heat sealing is used for many applications, including heat seal connectors, thermally activated adhesives, film media, plastic ports or foil sealing. Heat seal connectors are used to join LCDs to PCBs in many consumer electronics, as well as in medical and telecommunication devices. Heat sealing of products with thermal adhesives is used to hold clear display screens onto consumer electronic products and for other sealed thermo-plastic assemblies or devices where heat staking or ultrasonic welding are not an option due to part design requirements or other assembly considerations.
Heat sealing is used in the manufacturing of bloodtest film and filter media for the blood and many other test strip devices used in the medical field today. Laminate foils and films are heat sealed over the top of thermoplastic medical trays, Microtiter plates and containers to seal and/or prevent contamination for medical test devices, sample collection trays and containers used for food products. Medical and fluid bags used in the medical and food industries. Fluid bags are made out of a multitude of varying materials such as foils, filter media and laminates. Hot bar sealers- have heated tooling kept at a constant temperature, they use one or more heated bars, irons, or dies which contact the material to heat the interface and form a bond. The bars and dies have various configurations and can be covered with a release layer or utilize various slick interposer materials to prevent sticking to the hot tooling. Continuous heat sealers- utilize moving belts over heating elements. Impulse heat sealers- have heating elements of Nichrome placed between a resilient synthetic rubber and a release surface of film or fabric.
The heating elements are not continuously heated. When the materials are placed in the heat sealer, they are held in place by pressure. An electric current heats the heating element for a specified time to create the required temperature; the Jaws hold the material in place after the heat is stopped, sometimes with cooling water: this allows the material to fuse before stress can be applied. Hot melt adhesive can be applied in beads at the point of joining, it can be applied to one of the surfaces during an earlier manufacturing step and reactivated for bonding. Hot wire sealing – involves a heated wire that both cuts the surfaces and joins them with a molten edge bead; this is not employed when barrier properties are critical. Induction sealing is a non-contact type of sealing used for inner seals in bottle caps. Induction welding heat sealing by non-contact induction Ultrasonic welding uses high-frequency ultrasonic acoustic vibrations to workpieces being held together under pressure to create a weld.
A type of heat sealer is used to piece together plastic side panels for light-weight agricultural buildings such as greenhouses and sheds. This version is guided along the floor by four wheels. Good seals are a result of time and pressure for the correct clean material. Several standard test methods are available to measure the strength of heat seals. In addition, package testing is used to determine the ability of completed packages to withstand specified pressure or vacuum. Several methods are available to determine the ability of a sealed package to retain its integrity, barrier characteristics, sterility. Heat sealing processes can be controlled by a variety of quality management systems such as HACCP, statistical process control, ISO 9000, etc. Verification and validation protocols are used to ensure that specifications are met and final materials/packages are suited for end-use; the efficacy of heat seals is detailed in governing specifications and regulations. Quality management systems sometimes ask for periodic subjective evaluations: For example, some seals can be evaluated by a simple pull to determine the existence of a bond and the mechanism of failure.
With some plastic films, observation can be enhanced by using polarized light which highlights the birefringence of the heat seal. Some seals for sensitive products require thorough verification and validation protocols that use quantitative testing. Test methods might include: Seal Strength testing known as Peel Testing, measures the strength of seals within flexible barrier materials; this measurement can be used to determine consistency within the seal, as well as evaluation of the opening force of the package system. Seal strength is a quantitative measure for use in process validation, process control and capability. Seal strength is not only relevant to opening force and package integrity, but to measuring the packaging processes’ ability to produce consistent seals; the burst test is used to determine precession. The burst test is performed by pressurizing the package; the results for the burst test include the burst pressure data and a description of where the seal failure occurred. This test method covers the burst test
Seal hunting, or sealing, is the personal or commercial hunting of seals. Seal hunting is practiced in nine countries and one region of Denmark: United States, Namibia, Norway, Finland and Greenland. Most of the world's seal hunting takes place in Greenland; the Canadian Department of Fisheries and Oceans regulates the seal hunt in Canada. It sets quotas, monitors the hunt, studies the seal population, works with the Canadian Sealers' Association to train sealers on new regulations, promotes sealing through its website and spokespeople; the DFO set harvest quotas of over 90,000 seals in 2007. The actual kills in recent years have been less than the quotas: 82,800 in 2007. In 2007, Norway claimed that 29,000 harp seals were killed, Russia claimed that 5,479 seals were killed, Greenland claimed that 90,000 seals were killed in their respective seal hunts. Harp seal populations in the northwest Atlantic declined to 2 million in the late 1960s as a result of Canada's annual kill rates, which averaged to over 291,000 from 1952 to 1970.
Conservationists demanded reduced rates of killing and stronger regulations to avert the extinction of the harp seal. In 1971, the Canadian government responded by instituting a quota system; the system was competitive, with each boat catching as many seals as it could before the hunt closed, which the Department of Fisheries and Oceans did when they knew that year's quota had been reached. Because it was thought that the competitive element might cause sealers to cut corners, new regulations were introduced that limited the catch to 400 seals per day, 2000 per boat total. A 2007 population survey conducted by the DFO estimated the population at 5.5 million. It is illegal in Canada to hunt newborn harp seals and young hooded seals; when the seal pups begin to molt their downy white fur at the age of 12–14 days, they are called "ragged-jacket" and can be commercially hunted. After molting, the seals are called "beaters", named for the way they beat the water with their flippers; the hunt remains controversial, attracting significant media coverage and protests each year.
Images from past hunts have become iconic symbols for conservation, animal welfare, animal rights advocates. In 2009, Russia banned the hunting of harp seals less than one year old; the term seal is used to refer to a diverse group of animals. In science, they are grouped together in the Pinnipeds, which includes the walrus, not popularly thought of as a seal, not considered here; the two main families of seals are the Otariidae, Phocidae. The fur seal yields a valuable fur. Seals have been used for their pelts, their flesh, their fat, used as lamp fuel, cooking oil, a constituent of soap, the liquid base for red ochre paint, for processing materials such as leather and jute. Archeological evidence indicates the Native Americans and First Nations People in Canada have been hunting seals for at least 4,000 years. Traditionally, when an Inuit boy killed his first seal or caribou, a feast was held; the meat was an important source of fat, vitamin A, vitamin B12 and iron, the pelts were prized for their warmth.
The Inuit diet is rich in fish and seal. There were 150,000 circumpolar Inuit in 2005 in Greenland, Alaska and Canada. According to Kirt Ejesiak, former secretary and chief of staff to then-Premier of Nunavut, Paul Okalik and the first Inuk from Nunavut to attend Harvard, for the c. 46,000 Canadian Inuit, the seal was not "just a source of cash through fur sales, but the keystone of their culture. Although Inuit harvest and hunt many species that inhabit the desert tundra and ice platforms, the seal is their mainstay; the Inuktitut vocabulary designates specific objects made from seal bone, sinew and fur used as tools, thread, fuel, clothing and tents. There are words referring to seasons, place names and kinship relationships based on the seal. One region of Canada's north is inhabited by the Netsilingmiut, or "people of the seal." The title of Ejesiak's article acknowledged the pivotal 1991 publication entitled Animal Rights, Human Rights by George Wenzel, a McGill University geographer and anthropologist who worked more than two decades with the Clyde Inuit of Baffin Island.
Wenzel's "scholarly examination" of "the impact of the animal rights movement upon the culture and economy of the Canadian Inuit" was among the first to reveal how animal rights groups, "well-meaning people in the dominant society through misunderstanding and ignorance can inflict destruction" on a vulnerable minority. Inuit seal hunting accounts for the majority of the seal hunt, but just three percent of the hunt in southern Canada. Ringed seals were once the main staple for food, have been used for clothing, fuel for lamps, as delicacy, igloo windows, in harnesses for huskies. Though no longer used to this extent, ringed seals are still an important food and clothing source for the people of Nunavut. Called nayiq by the Central Alaskan Yup'ik people, the ringed seal is