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The current coronavirus 2019 disease (COVID-19) pandemic has greatly changed our perspective of the risk for infection from contact, and the use of personal protective devices (PPDs) usually reserved for health care workers (HCWs) has spread to the general population, sometimes indiscriminately. As a result, medical glove stock has been depleted, but most of all medical gloves have become a source of medical concern.[1], [2], [3], [4]

The World Health Organization (WHO) has warned about the limited protective efficacy of gloves. There is high risk for infection spread with their incorrect use that could instead favor the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Regular use of gloves for daily activities may lead to a false sense of protection and to an increased risk for self-contamination. This would involve the involuntary touching of the face or the spreading of fomites to desks, phones, and computers keyboards. A study has found that viruses can survive on gloves for 2 to 4 hours.5
Hand-to-face contact has a substantial role in upper respiratory tract infections,6 , 7 although COVID-19’s main way of transmission remains symptomatic person-to-person through respiratory droplets.[1], [2], [3], [4] The Centers for Disease Control and Prevention (CDC) and the European Center for Disease Prevention and Control (ECDC) have recently provided guidance to regulate the use of gloves both in the health care setting and in the community.2 , 4 In the context of the COVID-19 pandemic (Table 1 ), gloves are recommended when caring for confirmed or suspected COVID-19 patients, especially when there is the risk of contact with body fluids (eg, blood, wound care, aerosol-generating procedures).

Hand protection with gloves is essential in any medical procedure, because skin cleaning/disinfection alone does not remove all pathogens, especially when the contamination is considerably high. Nonsterile disposable gloves should be prioritized, and ECDC alerts that no direct evidence documents an increased protection against COVID-19 through glove use, compared with proper hand hygiene alone. Meticulous hand hygiene with water and soap or by alcohol-based hand rub solutions is not avoided by the use of gloves.

There are many different types of gloves, depending on the level of protection, tactility, risk of allergy, or cost (Table 2 ). Although biohazard risk requires frequent glove changing, the extended use of gloves, decontamination with hand disinfectants, and reuse are frequent.8 All of this should be avoided, because effects of hand sanitizers are tested on the skin, whereas application on gloved hands affects gloves’ mechanical properties. In a recent investigation,9 the application of 70% ethanol or 63% isopropanol commercial disinfectants reduced the tensile strength of latex and nitrile gloves, with a higher impact on nitrile gloves. Elongation did not change much with latex gloves, but nitrile gloves were affected. There are additional concerns about permeability, as alcohol can permeate any type of glove after 10 minutes. Some types of disposable gloves are permeated at 2 minutes, and repeated exposure to disinfectants can increase the permeability of the gloves. Alcohol is inactivated in the presence of organic matter, which can easily remain on used gloves, thus potentially driving the viral transmission.

Extended length gloves are not necessary when providing care to suspected or confirmed COVID-19 patients. They are not specifically recommended, except for activities with increased risk, such as submerging hands into a solution. For standard procedures, it is sufficient to cover the cuff (wrist) of the gown while donning.[1], [2], [3], [4]

Another common measure that is no longer recommended is “double gloving,” except for surgical procedures that carry a high risk of disrupting the integrity of the glove. Double gloving seems to increase the incidence of dermatologic side effects, from irritation and overhydration to induction of latex allergy. The increase of skin damage as the consequence of overzealous PPD use and hand hygiene is an emergent consequence of the COVID-19 handling.[10], [11], [12]

About 74.5% of front-line COVID-19 HCWs developed hand dermatitis in the Chinese experience.13 A questionnaire-based study suggested that 88.5% of skin reactions on the hands are associated with the use of latex gloves.14 Three types of adverse events might occur: latex allergy, talcum powder reactions, and irritant dermatitis. Excluding latex allergy and powder within the gloves, the problem of excessive dryness and pruritus, associated with irritant dermatitis, may be aggravated by occlusion, leading to sweating and/or overhydration. This then may increase the permeability to sanitizers or detergents, creating a vicious cycle, plus aggravation of hand dermatitis.12

A peculiar pattern of hand dermatitis has been recognized, characterized by erythema and fine scaling on the palms and web spaces.15 This may be attributed to the depletion of surface lipids, resulting in deeper penetration of detergents, and progressive damage of skin layers is a major pathogenetic mechanism. Irritant contact dermatitis is more commonly found with iodophors, chlorhexidine, chloroxylenol, triclosan, and alcohol-based products, whereas allergic contact dermatitis develops due to quaternary ammonium compounds, iodine or iodophors, chlorhexidine, triclosan, chloroxylenol, and alcohol sensitization.

To date, there have been no verified reports of COVID-19 infection as direct consequence of skin damage. Angiotensin-converting enzyme 2 (ACE2), which is the main cell receptor for SARS-CoV-2 entry, can be expressed in the basal layer of the epidermis, hair follicles, and eccrine glands, as well as on skin blood vessels.16

Basic skincare measures should be taken to avoid the risk of SARS-CoV-2 entry through the skin.[10], [11], [12], [13], [14], [15] Careful hand skin drying and hypoallergenic hand cream/emollients may be employed to prevent trapping sanitizers in the web spaces. Emollients may also be applied at other times to correct any residual dryness and scaling, or with the occurrence of hand dermatitis, topical corticosteroids are indicated.

A final consideration is the generation of massive amount of medical waste, caused in part by the extensive use of PPDs.17 HCWs, together with the general population, are using more gloves than ever before, whereas it should be limited to very essential preventive measures.


Medical gloves remain an essential part of the infection-control strategy; however, caring for patients with COVID-19 has pointed out the need for more accuracy and respect of novel guidance. Prolonged use of gloves, outside of direct patient contact, might be self-defeating rather than protective. Hand dermatitis is an emerging concern. At this time, the U.S. Food and Drug Administration has not cleared, approved, or authorized any medical gloves for specific protection against the virus that causes COVID-19 or prevention of COVID-19 infection.

Broadly speaking, there are 2 types of medical gloves: examination gloves, which are ambidextrous, usually nonsterile, and come in a small range of sizes, are used for nonsterile and less dextrous tasks and also for most dental work; surgical gloves are sterile, come individually packaged in handed pairs, and are usually available in half-inch intervals of hand girth. They are used in the operating theater for a variety of dextrous tasks, ranging from microsurgery on the eye or ear to bone setting or hip replacement.
Because the majority of clinical work is not perceived to be as dextrous as surgery, less emphasis is placed on the performance of examination gloves. Until recently, both examination and surgical gloves were generally made from natural rubber latex (commonly referred to as “latex”), although alternatives were available for known cases of latex allergy. However, the lack of regulation of manufacturing processes in the early years of mass production meant that gloves often contained a high level of allergenic proteins, which led to a steady increase in the number of cases of latex allergy reported.1

Current guidelines from the National Health Service and the Royal College of Physicians2 in the United Kingdom state that “the evidence does not … support a need to ban latex completely from the workplace.” They note that nonlatex surgical gloves “have higher failure rates in use and lower user satisfaction than latex gloves.” Instead, they advocate the use of nonpowdered, low-protein latex gloves, except for employees with latex allergy, latex sensitization, or latex-induced asthma, where nonlatex alternatives are recommended. However, most primary care health care groups and hospitals in the United Kingdom have replaced latex in nonsurgical situations with less flexible alternatives3 such as nitrile to remove the risk of latex allergy in patients and practitioners.
Similarly, the American College of Allergy, Asthma, and Immunology4 recommends that “a facility-wide review of glove usage should be undertaken to determine the appropriateness of use … and thereby prevent the unnecessary use of latex gloves” and advocates nonpowdered, low-protein gloves as standard in a health care facility but also states that “hospitals need to evaluate manufacturer information on nonlatex gloves in areas of durability, barrier protection, and cost” because “latex is still considered superior with respect to barrier characteristics against transmissible diseases.” Surgeons have generally resisted moves to replace surgical gloves in the same way because of the perceived reduction in manual performance when using nonlatex alternatives.

With respect to the glove design process, there is little or no evidence that gloves are evaluated in terms of their effects on users’ manual performance. All the currently available standards5,  6 focus on the barrier integrity of the gloves by defining tensile strength, freedom from holes, and tear resistance. Similarly, much of the research on medical gloves has concerned barrier integrity7,  8 and adherence of practitioners to handwashing and glove handling guidelines.9,  10 Clearly, because the primary role of the gloves is to prevent the spread of infection, it is important that the design brief takes these things into consideration, but achieving good barrier integrity is not necessarily incompatible with achieving the best performance.

Glove performance also has an effect on safety, particularly in a surgical environment. Surgeons using plastic gloves with less-than-optimal frictional properties, for example, may be more likely to drop instruments, to slip when performing delicate procedures, or to increase their stress levels when attempting to compensate. Similarly, practitioners who cannot feel a pulse through gloves when taking blood will be more likely to remove the gloves and increase their risk of infection. A 1994 survey of health care workers11 found that a “perceived interference with technical skills” was a common obstacle to compliance with universal precautions. There is also a subjective element to the performance that must be considered, which is that practitioners’ comfort and confidence in their gloves may affect their concentration levels and therefore their ability to perform surgery over extended periods of time.

It is vital that the glove design process includes an assessment of their effect on manual performance to ensure that practitioners can operate safely and efficiently. The first step in this process is to determine the key aspects of manual performance in medical practice and where current gloves have a significant adverse effect. The second is to design tests that are useful predictors of clinical performance. It is therefore necessary to identify the tasks that are most challenging and on which gloves are thought to have the greatest impact so that the tests can be designed to simulate relevant manual skills.

To achieve this, semistructured interviews with medical practitioners were carried out. As well as gathering information on the participants’ roles, disciplines, and glove use, a series of open-ended questions were used to identify tasks believed by users to require the most dexterity and tactility, and those most affected by glove performance, as well as any other issues related to HDPE gloves that might aid the study. The interviews took place within Sheffield Teaching Hospitals NHS Foundation Trust (STH) and received ethical approval from the research ethics committees of STH and The University of Sheffield, UK.

Focus groups were considered as a means of gathering data fairly quickly and stimulating discussion. However, the limited availability, particularly of senior staff, made this a difficult approach. Furthermore, it has been shown12 that, when recruitment, transcription, and analysis are included, focus groups can be much more time-consuming than individual interviews. Although focus groups are generally accepted to produce a wider range of responses, this is not always the case and depends on the nature of the questions.12,  13 In this study, many of the questions were of a technical nature and specific to the individual’s specialty. There was also a concern that participants’ opinions on specific gloves would be influenced by those of their colleagues.
Interviews were therefore conducted on a one-to-one basis to increase flexibility and enable senior staff to participate at their own convenience, often between operations or appointments. The questions were designed to be sufficiently open-ended so that the participant was not led down one particular line of thought but also included prompts where information was not forthcoming. With a wide enough selection of participants, it was hoped that a consensus would be formed in at least some of the areas, which would enable judgments to be made on the most productive direction for future research.

Solvent recovery is a form of waste reduction. In–process solvent recovery still is widely used as an alternative to solvent replacement to reduce waste generation. It is attractive, like end–of–pipe pollution control, since it requires little change in existing processes. There is widespread commercial availability of solvent recovery equipment which is another attraction. Availability of equipment suitable for small operations, especially batch operations, make in–process recovery of solvents economically preferable to raw materials substitution.

Commercially available solvent recovery equipment include:

Carbon adsorption of solvent, removal of the solvent by steam, and separation of the solvent for reuse in the operation. Carbon must be regenerated, two or more units are required to keep the operations continuous. Chloric acid formation from chlorinated solvents, carbon bed plugging by particulates, and buildup of certain volatile organics on the carbon and corrosion can be a problem.

Distillation and condensation can be used to separate and recover solvent from other liquids. Removal efficiency can be very high using this process and can be used for solvent mixtures as well as single solvents.

Dissolving the solvent in another material such as scrubbing. Solvents must be then recovered from the resulting solution, through distillation but efficiency of removal is often not high using this method.

Adsorption processes are useful and versatile tools when it comes to waste solvent recovery unit as they can be applied with high efficiency at relatively low cost in cases in which the desired component presents either a fairly small or a fairly high proportion of the stream. The applicable adsorbents vary according to different purposes.108,109 Adsorbents with low polarity (activated carbon, etc.) tend to adsorb nonpolar compounds, whereas ones with high polarity (e.g., silica, alumina) have higher affinity to adsorb polar substances. However, some adsorbents operate via specific binding sites (e.g., molecular sieves, molecularly imprinted polymers) rather than simple hydrophilic-hydrophobic interactions. It is worth mentioning that adsorption cannot easily be installed in a continuous configuration and is usually either a one-bed batch process or a twin-bed process with one bed in the adsorption, whereas the other one in the regeneration phase.

In organic solvent recycling, the most frequent issue is the removal of water content. Even traces of water can cause unexpected solubility problems, side reactions, or the decomposition of a reactant. There are various processes to recover wet solvents such as distillation methods or fractional freezing, whereas adsorptive methods are advantageous due to their low energy consumption. Molecular sieves (with pore size 3 or 4 Å), silica, and alumina are widely used for solvent drying.110,111 The polarity of the solvent affects the efficiency of water removal, which decreases with increasing polarity of the solvent. With the proper choice of adsorption technique, residual water content between 1 and 100 ppm is usually a realistic target.

In the regeneration stage of adsorption, high volumes of gas containing organic solvent are produced. Other processes in the chemical industry, such as paint drying or the drying of solid pharmaceutical intermediates or products, also generate a significant amount of solvent vapor.112 This raises another issue, as the recovery of this solvent is highly desired to minimize solvent loss and the environmental burden, as urged by the increasingly strict regulatory environment. For example, the recycling of chlorofluorocarbons has gained a lot of attention since the Montreal protocol.113–115 Incineration of solvent vapors is a widely used solution since it makes use of the solvent's latent heat. However, incineration likely needs supporting fuel to reach the required efficiency and needs continuous solvent vapor feed, not to mention that nonflammable halogenated solvent cannot be eliminated in this manner. Adsorptive systems have proved to be good alternatives. This field of adsorption is dominated by activated carbon adsorbents,116 but molecular sieve zeolites are also employed.117 Polymeric adsorbents are seldom employed in such processes, mainly because of their high price compared with activated carbon and zeolites.118 The choice of adsorbent regeneration technique has a significant effect on the quality of the recovered solvent. Examining the efficiency and applicability of various regeneration processes has been the aim of several studies.112,119 A typical system utilizing activated carbon adsorption to recover solvents from air emissions is shown in Fig. 3.15.11. Steam regeneration is employed to strip solvents from the activated carbon followed by condensation of the steam/solvent mixture through cooling. Eventually the solvent layer is separated by simple decantation.

The integrated production and recovery of ABE using glucose as a substrate and gas stripping as a means of solvent recovery distillation equipment has been reported by Groot et al. [39], Mollah and Stuckey [40], Park et al. [41], and Ezeji et al. [42–44]. Groot et al. produced butanol in a free cell (not immobilized) continuous reactor and removed the product in a separate stripper [39]. As a result of simultaneous product recovery, glucose utilization was improved by threefold, but the selectivity of butanol removal was low at 4 as compared to 19, which is the selectivity at equilibrium, suggesting that the stripper was not efficient. Also solvent productivity in the integrated system was 0.18 g/L h, as compared to 0.17 g/L h in the nonintegrated batch system [39]. Mollah and Stuckey used immobilized cells of C. acetobutylicum to improve productivity and recover butanol by gas stripping [40]. The cells were immobilized in calcium alginate gel and used in a fluidized bed bioreactor. This integrated system achieved a productivity of 0.58 g/L h, which is considered low for an immobilized cell continuous reactor.

Ezeji et al. tested the use of a hyper-butanol-producing strain, Clostridium beijerinckii BA101, in an integrated system with butanol produced in a free cell fed-batch reactor coupled with in situ product recovery [43]. As a result of simultaneous product recovery, the rates of fermentation (productivity) and glucose utilization improved. To compensate for the utilized glucose, a concentrated sugar solution (500 g/L) was intermittently fed into the reactor to maintain a solventogenic substrate concentration. This reactor was operated for 207 h before the culture stopped fermentation due to the accumulation of unknown inhibitory products. In this system 500 g/L glucose was used to produce 232.8 g/L ABE. ABE productivity was also improved from 0.29 g/L h in a nonintegrated batch system to 1.16 g/L h in the integrated system, a 400% increase. Given that the fed-batch fermentation stopped due to the accumulation of unknown inhibitory products, the authors devised another system in which a semicontinuous bleed was withdrawn from the reactor to eliminate or reduce the accumulation of unknown toxic by-products. As a result, the continuous reactor was operated for 21 days (504 h) before it was intentionally stopped [44]. Results from this continuous reactor suggest that ABE fermentation can be operated indefinitely in continuous mode, provided that toxic butanol is removed by gas stripping and unknown toxic products are removed by a bleed. In a 1-L culture volume, the system produced 461.3 g ABE from 1125.0 g glucose, with an ABE productivity of 0.92 g/L h, compared to 0.28 g/L h productivity in the nonintegrated batch system.

Adsorption is a physical process in which organic species are transferred onto the surface of a solid adsorbent. Adsorption is a particularly attractive control method as it can handle large volumes of gases of low pollutant concentrations. It is capable of removing contaminants down to very low levels.1 Removal efficiency is typically greater than 95%. The most frequently used adsorbent in the organic compound applications is activated carbon, although zeolites and resins are also used.

Adsorption is the most widely used solvent-recovery technique and is also used for odor control. The latter application is necessary to meet statutory air pollution control requirements. Depending on the application, adsorption can be used alone or with other techniques such as incineration.14
Solvent recovery with adsorption is most feasible when the reusable solvent is valuable and is readily separated from the regeneration agent. When steam-regenerated activated-carbon adsorption is employed, the solvent should be immiscible with water. If more than one compound is to be recycled, the compounds should be easily separated or reused as a mixture.9 Only very large solvent users can afford the cost of solvent purification by distillation.’

The advantages include the availability of long-term operating data. In addition, adsorbers can handle varying flow rates or varying concentrations of organic compounds. The main disadvantage of adsorption is the formation of a secondary waste, such as the spent adsorbent, unusable recovered organic compounds, and organics in the waste water if steam is used for regeneration. Secondary waste may require off-site treatment or specialist disposal.12 (see Table 13.12)

In addition to air, moisture and photochemical stability, the thermal stability is an important aspect of improving the economy of the process. The occurrence of thermally induced polymerization or decomposition reactions results in a loss of solvent recovery potential, specialized facilities for the treatment and post-purification of solvents and product streams and poor flexibility in the optimization of the thermal profile of the process (solvent extraction and extractive distillation steps). N-Methyl pyrrolidone has been shown to be chemically and thermally stable in the Arosolvan process. Sulpholane is reported to be stable to 493 K and undergoes some decomposition at 558 K [23]. In the sulpholane process, the influence of oxygen on solvent stability in the form of minor oxidative degradation has been observed under normal operating conditions. Consequently, the exclusion of air in the feed to the extraction unit has been advocated for this process together with the inclusion of a solvent regenerator unit. The latter operates by removing oxidized solvent from a small side-stream of the circulating solvent that is directed towards the solvent regenerator unit [16]. Ionic liquids exhibit excellent thermal stability and lack of sensitivity to oxygen would be advantageous with respect to the processing and recovery of the solvent.

Pfizer has redesigned the synthesis of several of its pharmaceutical products to reduce generation of hazardous waste. Changes were made in the synthetic route to sildenafil citrate (see Fig. 9.7), the active ingredient in Viagra® (Dunn et al., 2004), which resulted in a more efficient process that required no extraction and recovery system for solvent steps (see Fig. 9.8). The E-factor (Sheldon, 1992) for the process is 6 kg waste/kg product, which is substantially lower than an E-factor of 25–100, which is typical of pharmaceutical processes. Furthermore, all chlorinated solvents had been eliminated from the commercial process. During the medicinal chemistry stage in 1990, the solvent usage was 1816 L/kg, and the optimized process used 139 L/kg solvent, which was reduced to 31 L/kg during commercial production in 1997 and to 10 L/kg with solvent recoveries. Pfizer plans to replace t-butanol/t-butoxide cyclization with an ethanol/ethoxide cyclization. Combined with other proposed improvements, this is expected to increase the overall yield from 76–80% and further reduce solvent usage and organic waste.

A first point of economic comparison is the variable cost requirements of each process. Here, variable costs are defined as the sum of all raw materials costs plus the utilities cost for conversion of raw materials to product. All labor, overheads and depreciation costs are not included. On a variable cost basis, both the diacetate and diphenate routes show a distinct advantage over the acid chloride route. The largest component of the cost differential results from the high cost of the acid chloride monomers relative to the free acids. The second largest component arises because the acid chloride process inherently uses greater solvent volumes than the other two routes. Solvent losses which invariably occur contribute to increased variable cost as the solvent recovery processes are not completely efficient. Variable cost differences between the diacetate and diphenate processes are not very large. Both processes can be thought of as variations to reacting free diphenol with the free diacids. In the diacetate variation, acetic anhydride is consumed in forming the diacetate, but some of this cost is recouped by selling acetic acid — the process by-product. In the diphenate route, phenol is first consumed in monomer preparation, then recovered during the polymerization. The variable cost of the diacetate route may be slightly higher than that of the diphenate route due to the conversion of anhydride to acetic acid, but this disadvantage can be mitigated depending on the phenol recovery/recycle efficiencies in the diphenate process.

Secondly, the capital investment requirement required to construct facilities to practice each of the three process technologies can be compared. The acid chloride process is a low temperature, atmospheric pressure process and process fluid viscosities are low. Thus, standard design reaction equipment with low cost supporting utilities are used in the reaction area. However, polymer recovery would generally be accomplished by precipitation, washing and drying followed by extruder pelletization — operations which are capital intensive. Also, extensive used solvent recycler for sale is required in the acid chloride process, again leading to increased capital cost. Both the melt or solution diacetate and diphenate processes on the other hand are high temperature, high vacuum processes where process fluid viscosities reach very high values. For these processes, polymer reactors will require some special design features particularly with respect to agitation and heat transfer. Supporting utilities will be rather capital intensive. To balance these costs, however, product recovery is expected to be relatively simple, requiring only one or two melt processing operations most likely using a thin film polymer processor followed by an extruder. Solvent recovery requirements would be modest for the diacetate process but somewhat more costly for the diphenate process where large quantities of phenol (especially from monomer production) will require purification prior to recycle. Some difference in capital investment required for monomer production in the diacetate and diphenate processes is also expected. Diphenyl ester production is less attractive due to the more extreme reaction conditions required and the large phenol recycle streams. However, even with the noted differences, it is estimated that any of the three described processes could be built for approximately the same dollar amount per annual pound of polymer capacity at the 15 Mlb year−1 scale (1 kg = 2.2 lb).

On the paper machine, the size press is used to apply surface size to dried paper.182,183 Starch is the most frequently used binder in surface sizing. Besides raising surface strength, starch also imparts stiffness, lowers water sensitivity, reduces dimensional changes and raises air leak density of the sheet. In conventional practice, the sheet passes through a pond of starch dispersion held above the nip between two large rotating cylinders. In the nip a high, transient, hydrostatic pressure is developed. Excess starch dispersion is drained from the ends of the nip. The surface size is transferred to paper by capillary penetration, pressure penetration and by hydrodynamic force during nip passage.

The quantity of starch transferred to paper by a size press depends on several factors: concentration of dispersed starch in the surface size; viscosity of the starch dispersion; diameter of the size press rolls; size press pond height; cover hardness of the size press rolls; size press nip loading pressure; fluting corrugated paper machine speeds; wet-end sizing of the sheet; and water content of the sheet. The concentration of starch in the surface size liquid can range from 2% to ∼15%, depending on product requirements. Frequently, pigments and other materials are added, which further increases total dispersed and suspended solids content. The viscosity ranges from water thin to several hundred cP (mPa·s).

Viscosity of the starch dispersion is the primary rate-determining parameter for dynamic sorption of starch into paper during surface sizing. Surface size penetration into the capillaries of paper proceeds in lateral and normal directions. Lateral flow takes the shape of an ellipse, according to the bias of fiber orientation in machine direction.184 Contributions by wetting and capillary penetration decrease with increasing paper machine speed, while the contribution by hydrodynamic force increases with speed. As a consequence, starch pick-up will pass through a minimum at a specific speed. The hydrodynamic force depends on the angle of convergence (which is determined by the diameter of the rolls), by the nip length (which is influenced by the hardness of the roll covers), by the paper machine speed and by the opposing loading force between the two rolls. High liquid viscosity, large roll diameter, soft roll covers and high newspaper machine speed increase starch transfer, while high nip pressure counteracts these drivers. Starch cationization has no affect on pressure-driven penetration, provided the hydrostatic pressure is high and the viscosity of the dispersion is low.

The transferred liquid penetrates into the sheet according to the void space between fibers and pigment particles. During drying, starch attaches to the fibers and pigment, and reinforces the sheet by ‘spot welding’ and bridging between paper constituents. The ultimate location of the starch in the sheet can be affected by chromatographic partitioning behind a front of water that advances into the sheet. This effect will primarily occur in heavyweight paper and board and may lead to a gradient in starch concentration in the sheet from the surface to the interior and a weakening of internal bond at the ultimate location of free water. Starch application to the sheet induces some desizing due to coverage of hydrophobic patches by hydrophilic starch.

Application of surface size to paper carries with it the transfer of a substantial quantity of water. As an example, surface sizing of a 75 g/m2 (50 lb/3300 ft2) sheet (with 1% residual water content) by a 5% starch solution for a coat weight of 1.5 g/m2 (1 lb/3300 ft2/side) will raise the water content of the sheet to 43%. This large quantity of water will weaken the paper. Web breaks at the size press can occur, particularly when the sheet is also weakened as a result of edge cracks or holes.

Surface sizing can induce structural changes in the paper sheet185 due to the interaction of water sorption (which causes a relaxation of internal stresses) and machine direction tension (which increases anisotropy and creates additional stresses). Anisotropy can be lowered by reducing tension on the web during sheet passage through the size press and subsequent dryers, and by raising the moisture content prior to the size press.

When surface-sized paper leaves the size press, it will cling to a roll and has to be pulled off. The separation force due to film splitting depends on the free film thickness, its cohesiveness, and the rheological properties of the surface size, especially its viscoelasticity. Transfer defects, such as ribbing, orange peel, spatter or misting may result. It is important to control the starch viscosity, to use the correct take-off angle and to apply appropriate web tension. Surface-size splashing can occur due to the converging motion of paper sheet and roll surfaces in the pond and fluid rejection at the nip. Best pond stability is obtained at high or low viscosity, while intermediate viscosity is most prone to induce pond instability.

The same basic test liner paper machine used to produce writing and printing paper are also used to form paperboard. However, modern paper machines are limited in their ability to produce a single-layer paper sheet with a grammage above 150 g m−2. There are a number of reasons for this limitation. Primarily, thicker single-layer sheets are more difficult to dewater requiring excessive reductions in machine speed. Furthermore, the increased drainage forces applied to thicker sheets in the forming section would cause greater fines removal from the bottom of the sheet resulting in a rougher surface. The topside of a very thick sheet would also be adversely affected since paper is formed on fourdrinier machines layer by layer from the wire side up, which would allow extra time for the fibers in the top layer to flock and produce a ‘hill and valley’ appearance. The combination of these two effects would produce an unacceptably two-sided product.

Manufacturing multilayered paperboard from separately formed sheets provides a solution to the above-mentioned problems. The forming section of paperboard machines are composed of two, three, or even four forming sections that bring individual sheets together at the wet press. Paperboard machines are for this reason large and complex having heights that are two to three times greater than single-former machines. Any one of the former sections in a multilayer machine can be either a traditional fourdrinier or a modified fourdrinier equipped with a top-wire unit for additional dewatering capacity. The use of different furnishes in each former produces a final sheet that is engineered for specific stiffness and smoothness requirements.

Although initially forming two to three separately formed sheets of paper, a multilayer machine forms a single sheet of paperboard when the individual sheets of paper are combined together in the wet press. The individual single-layered sheets prior to the wet press are ‘vacuum dewatered’ with a typical consistency of 20% (80% moisture) and are simply assemblages of fibers held together by capillary forces exerted by the continuous matrix of water surrounding the fibers. When the sheet continues it progress through the wet press and the dryers, this continuous matrix of water is decreased and the fibers are progressively drawn together through surface tension. Eventually, at the end of the drying process with a final moisture content of 4–8%, the surface tension forces between individual fibers will produce pressures sufficiently high enough to form fiber-to-fiber hydrogen bonds resulting in a mechanically strong sheet. During multilayer forming, a single sheet of paperboard is formed from the individual sheets of paper by merging the water matrices of each sheet into a single, hydraulically connected matrix in the wet press. The net result is that the multilayer sheet continues through the wet press and dryer section forming fiber-to-fiber bonds inside layers and between layers as if they were initially formed together. Theoretically, the fiber-to-fiber bonding between separately formed layers will be identical to fiber-to-fiber bonding within a single layer. Differences in interlayer bonding strength (measured by z-direction strength tests) will be found when the individual sheets are wet pressed at moisture contents lower than what is necessary to form a hydraulically connected matrix. (z-direction strength is the maximum tensile force per unit area which a paper or paperboard can withstand when applied perpendicularly to the plane of the test sample.)

The advantage of manufacturing a multilayer sheet is that key paper properties can be engineered into the paperboard that would not be obtainable by single-layer forming. Special top layers can be incorporated that are white and smooth, therefore, having excellent printing properties. Middle layers can be used that are bulky and thus inherently thicker producing the stiffest possible board. These middle layers can also contain recycle fibers or pulp fibers of lower quality that can be covered or masked by higher quality top and/or bottom layers.
Although starch is usually added at the wet end of the coated board duplex paper machine as a liquid feed directly to the furnish, other systems which place the starch directly on the formed sheet while it is still on the wire of the Fourdrinier machine or on the felt of the cylinder machine may be used. Advantages claimed are improved retention and better distribution of starch throughout the sheet, while permitting the use of low-cost unmodified starch.

In one system, a solution of cooked starch or a dispersion of starch granules is sprayed from nozzles directly onto the wet-web of fibers. By varying concentration, spray pressure, and spray location, a variety of effects can be achieved (24, 25). Three types of spray systems are in use: high-pressure air atomization, high-pressure airless atomization, and low-pressure airless atomization. With high-pressure systems, an electrostatic assist is used to prevent loss owing to misting (26).

In another system, low-density starch foam is applied directly on the wet-web immediately before it enters the wet press. The foam is mechanically broken at the press nip, and the starch is dispersed through the sheet. By controlling foam density, bubble size, and starch concentration, a wide variety of results can be achieved (27). As in the spraying system, very high retentions are possible, and low-cost unmodified starch may be used.

In another system, a thin curtain of liquid is applied to the wet-web (28) for high retention of chemicals, including starches. This system is claimed to be suitable for addition of starch to multi-ply paperboard where it increases ply bond strength.

In the beginning was the hollowed-out tree trunk, one of the first capillary tube to be crafted by human hand. With a vast array of models in the plant world to inspire him, Homo sapiens had a much easier job inventing the tube than the wheel for which, by contrast, nature had no example to offer. Bamboo and reed are just two examples of plants with hollow stalks. Nature already knew the value of the tubular form, which combines high stability with the capacity to Transport essential substances for growth, such as water and nutrients, out of the earth.

In technical terms, a tube or pipe is a cylindrical, hard hollow body which usually has a round cross-section but can also be oval, square, rectangular or more complex in profile. It is used on the one hand to convey liquid, gas and solid matter and, on the other, as a construction element. Whatever its purpose, the term covers all sizes and diameters, from the smallest needle pipes right up to wind tunnels. No other profile shape with the same material cross-section has such a high flexural strength, which is what makes the tube so important as a load-bearing element in building.

Tubes for transporting purposes

In the past, people always tried to settle close to water. As the size of the settlements grew, it became increasingly difficult to get the water from the source - the spring, pond, river or lake - to the different dwellings. At first, people used open conduits - initially simple trenches, later stone canals. When the springs and sources were exhausted, aqueducts were used to carry water from the mountains into the towns. Some 300 years A.D., the Romans transported water from the Campagna into their capital and some of their impressive waterways can still be marvelled at in modern-day Europe.

Later, the open canals were covered over and used as closed conduits - and thus the pipeline was born. People were also quick to realize the benefits of closed pipes against open canals for removing waste water. Early pipe materials included wood and stoneware (fired clay), but also easy-to-work metals such as bronze, copper and lead. The first closed pipelines were made around 4,000 years ago of fired clay. The oldest metal pipelines date back to 200 years B.C., first made of bronze and later lead. Lead pipes were cast and chiefly used to Transport water. Copper pipes meanwhile were made from chased copper plate which was rolled and subsequently soldered together.

The advent of an economical method of producing large quantities of cast iron in the 14th century laid the foundation for the manufacture of iron pipes. Gunsmiths and cannon-makers were amongst the first to produce iron pipes. Cast iron pipes were used as early as the 15th century to carry water - some dating back to the 16th century are still in use today. Cast iron pipes also accompanied the development of a public gas supply network, for which compression-proof pipes were a matter of safety and therefore absolutely essential.

As more economical steelmaking methods were developed, an opportunity opened up for this material to be used for pipes. The first were forge-welded out of hoop steel, a method already known to gunsmiths in the Middle Ages. Around 1880, the invention of crossrolling by the Mannesmann brothers also made it possible to produce seamless pipes and tubes. With their thicker walls, seamless pipes offered greater stability at a relatively low weight. Oil-prospectors used such pipes to reach deeper reservoirs and by doing so were able to satisfy the growing demand for mineral oil which accompanied the early days of motorisation. The fact that mineral oil could be transported economically over long distances through a pipeline pushed up the demand for steel pipes even further. Soon, pipelines came to be the biggest market in this area, with demand reaching several million tonnes of welded and seamless pipes every year.

The crucial importance of how a pipe is made for the economic efficiency and environment-friendliness of industrial plant can be illustrated with the contemporary example of seamless boiler pipes with inner ribs. For years the power industry has been aiming to reduce fuel consumption and thereby cut CO2 emissions by stepping up efficiency. This can be done by working with higher operating pressures and temperatures. Consequently, plans have been made to set up new power plant in the first decades of the next century, which will run with pressure levels of up to 350 bar (today's maximum is 300 bar), at operating temperatures of around 700 "C (as opposed to 600 'C) and with efficiency increased from fts current 40% to 50%. Operating parameters of this kind can only be used for suitabie products and materials, of which seamless boiler pipes with inner ribs are one example. On account of their internal geometry, these pipes substantially improve the heat transfer between heating and the vapour phase on the inside of the pipe.

Pipes made of nonferrous metals and plastics Thanks to its good corrosion resistance, copper can be used to make pipes for the chemical industry, refrigeration technology and shipbuilding. Alongside their application for installation purposes, the usually seamless copper pipes are also used in capacitors and heat exchangers. For corrosive materials, low temperatures or stringent demands on the purity of the material carried by the pipe, Aluminium and Aluminium alloys are used in pipe construction. Meanwhile, thanks to its high resistance to many aggressive materials, titanium is well- suited to use in chemical engineering.

Plastics belong to the group of newer pipe materials. With the development of methods for producing plastics on an industrial scale in the 1930s, it also became possible to manufacture plastic pipes economically. By the middle of the 30s, plastics were already being used in Germany to make pressure pipelines. Among the chief advantages of plastics are their high corrosion resistance and a substantial chemical resistance to aggressive media. Moreover, the smooth surfaces mean that plastic pipes are not prone to incrustation, which can have a very detrimental effect on their conveying capacity. Pipes supplying drinking water are mostly made of polyethylene (PE) or polyvinyl chloride (PVC). Like ABS (acrylonftrile-butadiene-styrene copolymer) plastics, these two materials are also used for gas pipelines. Thermoplastic materials - alongside PE and PVC these include PP (polypropylene) and PVDF (polyvinylidenefluoride) - can also be used for industrial pipelines. Beyond these, PB (polybutene) and PE-X (cross- linked polyethylene) are also widespread in pipe-making. Plastic pipes find application in areas such as heating technology, shipbuilding, underwater pipelines (the crossing below a river floor from one bank to the other), irrigating and drainage plant, and well-building.

The right choice of material has a crucial bearing on the economic efficiency and safety of a pipe system. Materials therefore have to be selected according to the demands of each specific application. In steel boiler construction, for example, pipes must be made of steel with high temperature stability plus heat and scaling resistance, while special corrosion resistance is all-important in the chemical and foodstuffs industries. Meanwhile, the mineral-oil processing industry requires heat- proof or press-water-resistant steels for its pipes, gas liquefaction and separation, on the other hand, need materials which have special strength at low temperatures. This broad and highly diversified range of requirements has put a fantastic array of materials to use in pipe- making. Alongside the iron and steel, nonferrous metals and plastics mentioned above, these also take in concrete, clay, porcelain, glass and ceramics.

In addition to liquids and gases, solid matter, broken down, as dust or mixed with water in slurry form, is also pumped through pipelines. Gravel, sand or even iron ore can be conveyed in this manner. Pneumatic transportation of grain, dust and chips through pipes is also a widespread practice. Pneumatic tube conveyors, which similarly work with air, are another important mode of transporting solid matter.

Pipes may be several meters in diameter and pipelines many kilometers in length. At the other end of the scale are conduits with tiny, barely perceptible dimensions. One example of their use is as cannulas in medicine - a collective term referring to instruments with a variety of applications, including infusions, injections and transfusions. Their outer diameter ranges from over 5 millimeters to as little as 0.20 millimeters. Cannulas are made of high-quality grades of stainless steel, brass, silver or nickel silver (an alloy of copper, nickel and zinc, sometimes admixed with traces of lead, iron or tin), but also plastics such as polyethylene, polypropylene or Teflon. Often, different materials are combined with one another to produce the individual components. These tiny tubes must have extremely pronounced elastic properties. They may bend but under no circumstances snap. Their surfaces are often nickel[-plated and always highly polished, sometimes even on the inside. The best-known cannulas are hypodermic needles which, in their most common form as sterile disposable syringes, guarantee aseptic use without costly preparation for reutilisation.

Tubes for construction

No matter where we look in our cities today, we can be sure to see tubular steel constructions. They have become an indispensable element of modern building technology. Once again, we took the idea from nature: in tube-shaped straws, bamboo shoots, quills and bones, Mother Nature demonstrated the successful marriage of beauty and function. Yet these excellent static properties remained unexploited until the advent of welding technology made it possible to connect virtually all dimensions of pipes perfectly and with the necessary interaction of forces for use as construction elements.

As an extremely lightweight building element, steel tube combines high strength with low weight. Steel tubes are used as deck supports in shipbuilding, supports in steel superstructures and binders in building construction. They are used as tubular and lattice masts for overhead and overland transmission lines, for trains and trams, and for lighting. Bridges, railings, observation towers, diving platforms, television towers and roof constructions in halls or sports stadiums are all further examples. Steel tube is also a popular" building element for constructions in temporary use, such as halls, sheds, bridges, spectator stands, podiums and other structures for public events, supporting structures and scaffolding, from the small-scale for house renovation right up to building scaffolds.

In plant engineering, steel tube is used to make ladders, shelves, work tables and subframes for machinery and plant. Steel tube also found its way as a construction element into precision components for machinery and equipment. Shafts and rolls or cylinders in hydraulics and pneumatics are just two examples. Beyond these applications, a great volume of steel tube is used in the cycle industry, camping equipment manufacture, the furniture industry, vehicle and car making and the domestic appliances industry.

Be it on water, over land or in the air, the various modes of Transport would be lost without pipes & tubes. Pipes and tubular construction elements are to be found in ships, planes, trains and motor vehicles. A great variety of pipes and tubular profiles are used in car making, both in connection with the motor and with the chassis and bodywork sections. Most recent developments put them to a far more varied range of uses than before, from air suction pipes and exhaust systems through chassis components right up to side-impact tubes in doors and other safety features. One German car makers new lightweight concept takes as its basic subassembly a three-dimensional frame made up of complex Aluminium extruded sections joined together with the aid of pressure-diecast intersections.

Pipes in everyday use

We come into contact with pipes and tubes on a daily basis. It starts in the morning when we go to clean our teeth and squeeze the toothpaste from this tube, which is nothing other than a tube-shaped flexible container. We write notes with a pen, comprising one or more tubes with a smaller tube - the cartridge or refill - inside it. This is the modern equivalent of the quill, a pointed and split tube used in ancient times as a writing instrument and still used today for Arabic script.

We are surrounded everywhere we go and on a virtually constant basis by seamless pipe ＆ tube, whether at home, on the move or at work. They take the form of lamp stands and furniture elements in chairs or shelves, curtain rails, telescopic aerials on portable and car radios, and rods on umbrellas or sunshades. And when we water the plants or hang out the washing, tubes are our constant companion - on the watering can or the clothes-horse. Pipes Transport electricity, water and gas directly into our homes. Tubes protect visitors to the Duesseldorf Trade Fair Center from the rigours of the Rhineland weather. Pipe constructions are responsible for a pleasant indoor temperature and prevent the hall roofs from falling on our heads. Civil engineers and architects choose special section tube constructions for windows and doors in preference to other solutions. Tubes even have a role to play in our leisure time, providing us with bicycles, training apparatus and sports equipment.

Musical pipes

Musical instrument-making would be unthinkable without welded pipe ＆ tube. The tuba illustrates the connection particularly well: the name of this brass instrument is nothing other than the Latin word for tube. Other brass and pipe instruments also take the tube form. The reed used in a variety of wind instruments such as the clarinet, saxophone, bassoon or oboe is a flexible piece of cane which is fixed into the mouthpiece of the instrument or acts as a mouthpiece itself. Organ pipes also rely on the tube shape to create their sound. They are made of lead and tin, zinc or copper and are still crafted today according to a centuries-old Tradition.

CD stands in the shape of organ pipes make for an original link between two musical words. These CD stands are just under two meters in length, accommodate up to 50 CDs and, if required, can be supplied with interior lighting. Normally out of sight but critically important for good sound quality are the bass-reflex pipes found in loudspeakers. With the proper dimensions in length and diameter, these pipes help to reproduce low-pitched tones without any distortion as a result of unwanted flow noise.

Through squre pipe ＆ tube flows the lifeblood of progress and without them our lives would not be nearly as comfortable. They make everyday life easier, safer, more attractive, more varied and more interesting. More to the point, though, they have become indispensable for our existence, shaping the development of our lives to lasting effect in the past and undoubtedly continuing to do so in the future.