In conservation, having a pH of under 7. Acidic substances can weaken the cellulose in paper materials, often causing the paper to become brittle and/or discolored.
Implies that a material has a pH of 7 or higher. However, this may only be true at the time of manufacture. Substances found in some papers such as lignin and certain additives may still lead to the formation of acid over time.
The term "Acrylic" most commonly refers to Polymethyl Methacrylate. Polymethyl Methacrylate is abbreviated PMMA and is typically used in the lenses of exterior lights of automobiles. Acrylic has a density that is less than half the density of glass, and similar to that of other plastics. Acrylic has good impact strength, higher than that of glass or polystyrene, but significantly lower than that of polycarbonate or engineering polymers. In the majority of applications, Acrylic will not shatter but instead breaks into large dull pieces. Acrylic is softer and more easily scratched than glass. Scratch-resistant coatings (which may also have other functions) are often added to Acrylic sheets.
In conservation, having a pH of over 7. Alkaline substances such as magnesium carbonate and calcium carbonate may be added to a material to neutralize the acids contained within or as an alkaline reserve or buffer.
An alkaline substance often added to paper storage materials to counteract the acids that may form in the future and to help absorb acids from artifacts. Alkaline-buffered storage materials usually have a pH of between 7.5 and 9.
A term often used to describe various materials, it is meant to imply that the materials in question are of a quality that is appropriate for artifact storage or treatment. This may or may not be true. The word archival is not strictly defined or regulated, and therefore may be used at will by manufacturers.
See Alkaline Reserve
The force of pounds per square inch required to rupture or burst the side of a cardboard box and is determined by the Mullen Test. This method indicates the box's ability to withstand external or internal forces and how the box will contain its contents during rough handling. For example, a box with a burst strength of 200 lbs. per sq. inch indicates that the cardboard used to make the box can withstand 200 lbs. of pressure per square inch.
The structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms. Cellulose is the most common organic compound on Earth. About 33 percent of all plant matter is cellulose (the cellulose content of cotton is 90 percent and that of wood is 50 percent). For industrial use, cellulose is mainly obtained from wood pulp and cotton. It is mainly used to produce paperboard and paper; to a smaller extent it is converted into a wide variety of derivative products such as cellophane and rayon.
Clay Coated News Back
Clay Coated News Back is abbreviated CCNB and is a recycled paperboard. Recycled paperboards are made from pre-consumer and post-consumer waste. Pre-consumer waste is mill conversion waste. Post-consumer waste consists of paper products that have been used and discarded. Recycled paperboard is six to nine ply, and has less desirable qualities than Solid Bleached Sulfate (SBS). Clay Coated News Back is typically coated with a thin layer of kaolin clay over a top ply of white recovered fiber to improve its printing surface.
The treatment of artifacts to help extend their survival and usefulness while at the same time maintaining their original integrity as much as is possible.
A material whose chemical structure is made of long chains of two differently structured chemical units (Monomers) which repeat a more or less regular pattern in the chain.
Corrugated Paper Board
Corrugated Paper Board is more commonly known as "cardboard". Corrugated board is made largely of recycled paper and most commonly is comprised of three components: an outer and inner liner, and a corrugating medium, commonly referred to as the "fluting", which is glued between the liners. It is this sandwich-type construction that gives corrugated board its excellent rigidity and structural strength as well as its unique cushioning characteristics. Over the decades, corrugated board has evolved and developed to provide a wide range of products for different applications. Standard and non-standard categories of corrugated board are based on the type of flute, whether coarse, fine or extra fine and the number of fluted walls whether single, double or triple layered.
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds and stencils, dies are generally customized to the item they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology.
Edge Crush Test
The Edge Crush Test (ECT) measures the stacking strength of corrugated cardboard boxes or fiberboard. Determining a finished box's compression strength is defined by the amount of force that is needed to crush cardboard by standing it on its edge. This test is also measured in lbs. per square inch. For example, a box with an ECT of 32 lbs. per square inch indicates that the board, standing on edge, can withstand a force of 32 lbs. per square inch before crushing.
A thermoset or thermoplastic with long polymer chains cross-linking during curing. The elasticity is derived from the ability of the long chains to reconfigure themselves to distribute an applied stress. The covalent cross-linkages ensure that the elastomer will return to its original configuration when the stress is removed. As a result of this extreme flexibility, elastomers can reversibly extend from 5 to 700%, depending on the specific material. Without the cross-linkages or with short, uneasily reconfigured chains, the applied stress would result in a permanent deformation. Elastomers that have cooled to a glassy or crystalline phase will have less mobile chains, and consequentially less elasticity, than those manipulated at temperatures higher than the glass transition temperature of the polymer.
Involves placing a document between two sheets of transparent polyester film, then sealing all four edges of the film. This provides the document with support and helps protect it from possible damages incurred through handling. Encapsulation differs from lamination in that the document is not adhered to the polyester, but instead may be removed at any time by cutting along the edges of the polyester. Encapsulation is not suitable for all documents, as the microclimate inside the capsule may actually accelerate the deterioration of an acidic document. For this reason, a sheet of alkaline buffered paper is often included behind a document in an encapsulation to help absorb some of the acids. Encapsulation is particularly appropriate for very brittle or fragile documents, and for those documents that will be handled frequently.
One of the most common plastics processing techniques covering a vast range of applications in which resins are melted, heated and pumped for processing. Extrusion machines accomplish these tasks by means of one or more internal screws. In extrusion, the material to be processed is sheared between the root of the screw and the wall of the barrel that surround it. This process produces frictional energy that heats and melts the substance as it is conveyed down the barrel. Melted extrudate from the machine is further processed after the extrusion phase, which typically produces pellets, sheet, cast film, blown film, fibers, coatings, pipes, profiles or molded parts.
Flute size refers to the number of flutes per lineal foot in corrugated paper, although the actual flute dimensions for different corrugated manufacturers may vary slightly. Measuring the number of flutes per lineal foot is a more reliable method of identifying flute size than measuring board thickness, which can vary due to manufacturing conditions. Common flute sizes are "A", "B", "C", "E" and "F". The 'B' flute is the most widely used. It is very difficult to crush and has good compression strength. The 'C' flute is larger with greater compression strength but offers less crush resistance and requires more space.
Grams per Square Meter: The standard unit of measure for the weight of paper or fabric.
The process of joining two or more thermoplastic films or sheets by heating areas in contact with each other to the temperature at which fusion occurs, usually aided by pressure. When the heat is applied by dies or rotating wheels maintained at a constant temperature, the process is called thermal sealing. In impulse sealing, heat is applied by resistance elements which are applied to the work when relatively cool and then rapidly heated. Simultaneous sealing and cutting can be performed by this method.
High Density Polyethylene
High Density Polyethylene is abbreviated HDPE and is another chemically stable plastic often used for storage of paper artifacts. It is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging (notably the plastic shopping bag). Polyethylene is not considered biodegradable, as it takes several centuries until it is efficiently degraded, except when exposed to UV from sunlight. SPI resin identification Recycling No. 2.
Hindered Amine Light Stabilizers
Hindered Amine Light Stabilizers is abbreviated HALS and is a group of additives having a common chemical structure as part of their molecule. These highly effective UV stabilizers protect the polymer by scavenging free radicals.
A manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. After a product is designed, usually by an industrial designer or an engineer, molds are made by a mold maker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part.
A paper produced by a modified sulfate process using only wood pulp. It is a relatively coarse paper and is known especially for its strength. Grocery bags are typically made of kraft paper.
The kraft process (also known as kraft pulping or sulfate process) describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers. The process entails treatment of wood chips with a mixture of sodium hydroxide and sodium sulfide, known as white liquor, that break the bonds that link lignin to the cellulose.
A joint made by lapping one material over another to provide a mated area that can be joined with an adhesive.
A process, not often used anymore by conservation professionals, by which a document is reinforced with transparent sheets of plastic. The high heat and pressure used during lamination, together with the instability of the materials used and the difficulty of removing the item from the laminate has made this method a generally unacceptable practice for items of any enduring value or importance.
A component of the cell walls of plants. Lignin is unstable, light sensitive, and breaks down into acid compounds as it ages. Its presence in paper items contributes to their degradation over time. Lignin is found in large amounts in wood, the plant fiber most often used to make paper since the middle of the 19th century. Lignin can, to a large extent, be removed during the papermaking process, resulting in a higher quality paper.
Linerboard is the grade of paperboard used for the outer "facings" of a corrugated box. Kraft linerboard is made from wood fiber derived by the kraft process and typically contains no more than 20 percent recycled material.
Linear Low Density Polyethylene
Linear Low Density Polyethylene is abbreviated LLDPE and is used predominantly in film applications due to its toughness, flexibility and relative transparency. LLDPE is the preferred resin for injection molding because of its superior toughness and is used in items such as grocery bags, garbage bags and landfill liners.
Low Density Polyethylene
Low Density Polyethylene is abbreviated LDPE and is commonly used in flexible bags for dry cleaning, trash, produce and bread, shrink wrap, and in some rigid containers for food storage. LDPE is slightly waxy, flexible, and stretches. It floats on water and smells like a candle when burned. Recycled LDPE is often used to make grocery bags, agricultural film, and plastic lumber. SPI resin identification Recycling No. 4.
A micrometer or micron is one millionth of a meter, which is equivalent to one thousandth of a millimeter or one thousand nanometers. The micrometer is a common unit of measurement for wavelengths of infrared radiation. The name micron is used, especially in astronomy and in the semiconductor industry, to denote a micrometer.
The ability of a chemical or compound to move from one material to another. One example of migration is acid migration which is when acid moves from an acidic material to a material of lesser or no acidity. This can be seen in the form of the brown marks on the pages of a book from a newspaper clipping placed within.
A unit of thickness often used when describing plastics used for the storage and treatment of artifacts. One mil (.001) equals one thousandth of an inch.
Mils to Microns conversion
To convert mil to microns, multiply the mil by 25.4 to arrive at true micron thickness. To convert microns to mils, divide the micron by 25.4 to arrive at true mil thickness (1 mil=25.4 microns). Example: 3 mil x 25.4 = 76 microns or 50 microns ÷ 25.4 = 2 mil.
An atom or a small molecule that has the potential of chemically binding to other monomers of the same species to form a polymer. The most common biochemical monomer is glucose, which is linked by glycosidic bonds into polymers such as cellulose and starch, and is over 76% of the weight of all plant matter.
In conservation, having a pH of 7; in other words, neither alkaline nor acidic.
A low-cost, low-quality, non-archival paper. It is usually made by a mechanical milling process, without the chemical process that is usually used to remove lignin from the pulp. The pages of a comic book are typically made from recycled newsprint.
A measure of acidity or alkalinity. The pH scale runs from 0 to 14. Each number increment indicates an increase of tenfold. Neutral pH is 7. Any number below 7 is acidic, with 1 being the most acidic. Any number above 7 is alkaline, to a maximum alkalinity of 14.
Also known as phthalate esters, are esters of phthalic acid and are mainly used as plasticizers which are substances added to plastics to increase their flexibility, transparency, durability, and longevity. Phthalates are primarily used to soften polyvinyl chloride (PVC).
One of many high-polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture, every plastic is capable of flowing, under heat and pressure if necessary, into the desired final shape.
Additives that increase the plasticity or fluidity of the material to which they are added. These materials include plastics, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concrete the desired effect is slightly different. Plasticizers for concrete soften the mix before it hardens, increasing its workability or reducing water, and are usually not intended to affect the properties of the final product after it hardens. The plasticizers for plastics soften the final product increasing its flexibility.
A unit of thickness often used when describing paper or board. One point equals one thousandth of an inch and is equivalent to one mil. For example, paper that is 40 mils in thickness (.040) is referred to as a 40-point paper.
One of the plastics that are recognized as being safe for storage of paper artifacts because of its chemical stability. Frequently used for sleeves, folders and encapsulations, conservation grade polyesters are Mylar D and Melinex 516 by DuPont.
Polyethylene Terephthalate is abbreviated PET and is a thermoplastic polymer resin made from polyester. Polyethylene Terephthalate is also called PETE, PETP, and PET-P. PET is referred to as simply polyester while PET is most often used to refer to packaging applications. SPI resin identification Recycling No. 1.
A large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties.
The third chemically stable plastic often used in the manufacture of enclosures for storing paper artifacts. Polypropylene sheets, also referred to as pages, are a popular choice for trading card collectors. These sheets come in various configurations, the most popular of which is the nine pocket page for standard size trading cards. Trading cards are inserted into each pocket and the pages are then stored in a binder. SPI resin identification Recycling No. 5.
An inexpensive hard thermoplastic substance, which is in solid (glassy) state at room temperature. The outside housing of the computer you are using now is probably made of polystyrene. Model cars and airplanes are made from polystyrene, and it also is made in the form of foam packaging and insulation (StyrofoamTM is one brand of polystyrene foam). Clear plastic drinking cups are made of polystyrene. So are a lot of the molded parts on the inside of your car, like the radio knobs. Polystyrene is also used in toys, and the housings of things like hairdryers, computers, and kitchen appliances. SPI resin identification Recycling No. 6.
Polyvinyl Chloride is the plastic known at the hardware store as PVC. This is the PVC from which pipes are made, and PVC pipe is everywhere. The plumbing in your house is probably PVC pipe. The "vinyl" siding used on houses is made of Polyvinyl Chloride. Inside the house, PVC is used to make linoleum for the floor. PVC is useful because it resists two things that naturally oppose each other: fire and water. Because of its water resistance Polyvinyl Chloride is used to make raincoats and shower curtains. It also has flame resistance because it contains chlorine. PVC can degrade as it ages, emitting hydrochloric acid, which can be very damaging to paper-based collectables. Flexible vinyl products contain additional chemicals to change the physical properties of the material called plasticizers which can migrate. SPI resin identification Recycling No. 3.
Radio Frequency Welding
Radio Frequency Welding is also known as RF Welding. Two pieces of material are placed on a table press that applies pressure to both surface areas. Dies are used to direct the welding process. When the press comes together, high frequency waves (usually 27.12 MHz) are passed through the small area between the die and the table where the weld takes place. This high frequency field causes the molecules in certain materials to move and get hot, and the combination of heat and pressure causes the weld to take the shape of the die. This type of welding is used to connect polymer films used in a variety of industries where a strong consistent leak-proof seal is required. The most common materials used in RF welding are PVC and polyurethane. It is also possible to weld other polymers such as nylon, PET, EVA and some ABS plastics.
Solid Bleached Sulfate
Solid Bleached Sulfate is abbreviated SBS and is a premium paperboard grade that is produced from a furnish containing at least 80% virgin-bleached wood pulp. Most bleached paperboard is coated with a thin layer of kaolin clay to improve its printing surface and may be also coated with polyethylene resin for wet strength food packaging.
Stabilizers increase both virgin resin's and post-consumer plastic's strength and resistance to degradation. Heat stabilizers provide resistance to thermal degradation during periods of exposure to elevated temperatures. Thermal degradation is reduced not only during processing but also during the useful life of the finished products. Light stabilizers are used in a variety of resins to limit the effects of sunlight or other sources of ultra violet radiation. Antioxidants can be used as sacrificial additives to protect plastics from oxidizing environments.
A polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high molecular weight polymers whose chains associate through weak Van der Waals forces (as in polyethylene); stronger dipole-dipole interactions and hydrogen bonding (as in nylon); or even stacking of aromatic rings (as in polystyrene). Thermoplastic polymers differ from thermosetting polymers in that they can be melted and remolded.
A polymer material that irreversibly cures. The cure may be done through heat, through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuits.
Abbreviated UVA, UV Absorbers are a group of additives which protect organic materials by absorbing the UV radiation.
A class of UV Absorbers which totally block UV light.
Any chemical compound which, when admixed with a thermoplastic resin, selectively absorbs UV rays and minimizes chemical and/or physical changes that may be engendered by UV.
The range of electromagnetic radiation from 150 to 400 nanometers. In solar radiation, there is a significant amount only over 250 nanometers.
The range of electromagnetic radiation from 400-800 nanometers.