What Do We Know So Far on Hair Straightening?


Hair represents a valued aspect of human individuality. The possibility of having an easy to handle hairstyle and changing it from time to time promoted an increasing search for chemical hair transformations, including hair straightening. Hair straightening is the process used to convert curly into straight hair. The desire for straight hair used to be associated with the standards of the “universal beauty.” Currently, the preference for this style is more for the ease of handling and the simpler daily care routine [1]. Straightening may be physical or chemical processes and temporary or permanent, regarding its duration.






We performed a literature search in the scientific database MEDLINE through PubMed until July 15, 2020, using the terms “straightening” AND “hair” (125 results), “straightening” AND “alopecia” (22 results), and “straightening” AND “human hair” (103 results). We limited the search to articles available in English and considered those mentioning alternatives to straighten the hair. After excluding duplicate titles, we had a total of 33 relevant articles.






Anatomically, the hair shaft has 3 layers: cuticle, cortex, and medulla [2, 3]. The outermost part is the cuticle, which is composed of keratin and consists of layers of scales overlapping 1 and other, just like tiles on a roof. The cuticle protects the underlying cortex and acts as a barrier [3-5]. The normal, undamaged cuticle has 6–8 layers according to the ethnicity, a smooth surface, allowing reflection of light and limiting friction between shafts [5]. The outer surface of the cuticle’s scale cells is coated by a thin membrane, the epicuticle, and each cuticle cell consists of 3 layers of protein: the A-layer, a resistant layer with high cystine content; the exocuticle, also rich in cystine; and the endocuticle, low in cystine content. The cortex accounts for most of the hair shaft and is responsible for the hair. The cortex is comprised of microfibrils, long filaments oriented parallel to the axis of the fiber. Each microfibril consists of keratin intermediate filaments, also known as microfibrils, and the matrix, constituted by keratin-associated proteins [4]. It is the thickest layer located around the medulla, which is the innermost part of the hair, has melanin granules which composition is related to the shades of hair color. It is also responsible for hair volume, the great tensile strength, and mechanical resistance of the shaft, as it contains the most part of keratin [3-5].






The primary component of the hair fiber is keratin. The remaining constituents are represented by other proteins, water, lipids, pigments, and trace elements. Because of its specific conformation and chemical bonds, keratin is responsible for hair stiffness, strength, and insolubility. Among the amino acids that make up keratin, cystine is one of the most important. Each cystine unit contains 2 cysteine amino acids from different portions of the peptide chains that are connected by 2 sulfur atoms, forming a strong bond named disulfide bridge [3-5]. Another important structural component of the hair shaft is the 18-methyl eicosanoic (18-MEA) acid. It forms a hydrophobic layer that retards water from wetting and penetrating and changing the hair shaft physical’s properties. Removal of the fatty acid layer decreases the brightness of the hair, making it more susceptible to static electricity and frizzing induced by humidity [4].






The spiral shape of the hair is determined by the asymmetric protein expression in the hair follicles [2]. As it is not possible yet to modify the shape of the follicle, the only way to change hair appearance is by modifying its physicochemical properties [6].






This method was developed in the late 19th century and became popular in the early 20th century by Madame C.J. Walker, who combined hot comb with pressing oil. It is a temporary straightening since it changes only weak hydrogen bonds, in a process named keratin hydrolysis. The initial technique was the application of a petrolatum ointment base in the hair, followed by straightening it using a heated metal combing device. Over time, the technique was improved. However, with the introduction of new methods, the hot comb went out of use [1, 5, 7, 8].






Physicochemical techniques combining mechanical and thermal straightening, as hairdryer and flat iron, are temporary solutions that last until the next washing. The hair needs to be wet, so hydrogen bridges break and there is the transitional opening of the helical structure of the shaft, relaxing it. The combined use of the dryer and the flat iron dehydrates the hair, keeping it straight [1].






High temperatures, between 235 and 250°C in the dry hair and 155–160°C in the wet hair, may denature hair shaft proteins [1, 9]. Usually, hairdryers are more harmful to the hair shaft than naturally drying it [9]. However, a study showed that the use of the dryer with continuous movement, at a minimum distance of 15 cm from the hair, could be less damaging than natural drying [10].






Hydroxides are potent alkalis, widely used for straightening very curly hairs [11]. The primary substances of this group and their characteristics are described in Table 1. Sodium hydroxide, also known as lye, is indicated for straightening extremely curly hair. No-lye relaxers, such as guanidine hydroxide, are indicated for straightening wavy to curly hair and for sensitive scalp. Although milder for the scalp, it leaves calcium mineral residues on the hair shaft, making it drier, brittle, and dull [4, 11-14].






STRAIGHTENING MY HAIR is typically a two-day affair. I wash all the product out the night before and load my hair with hydrating protectants. I let it air-dry, then I braid it before bed so that the next day, the curls are looser and easier to work through. Then, and only then, can I go in with a flat iron.






WIRED's Gear members have an array of curl types, needs, and hair-styling tricks, and we've all tried a lot of hair straighteners in our lifetimes. Some flat irons have left us with crispy ends and cramped hands, while others, like the ones listed here, gave us sleek hair. There's a dizzying number of options around, but hopefully our favorite titanium hair straightener can help narrow down your search.






Updated December 2021: We've added more of our favorite tourmaline hair straightener, including the Bio Ionic 3-in-1 tool, the L'ange iron that blows cool air, and two honorable mentions. 






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Modern technologies have come up with ceramic hair straightener that are user-friendly. You no longer have to visit a salon if you want straight hair. However, using a hair straightener may not be easy for someone who has not used it before. Though flat irons are simple to use, one needs to be aware of the associated factors to ensure safety. If you are a beginner, here is a simple guide on how to use hair straightener at home.






Before you straighten hair at home, you need to prep your hair. Pollution, grease, various styling products, and dirt make your hair frizzy and unmanageable (1). Therefore, you need to wash your hair before straightening it.






Use a hydrating and nourishing shampoo to make your hair soft. Before you apply the flat iron on hair, make sure your hair is dry. Do not use a hair straightener on wet hair.






Choosing the right type of hair straightener is as important as preparing your hair for the straightening method. The market is flooded with plenty of straightening brands, and the abundance of options may end up confusing you. Here Checkout these Hair Straighteners as few options you can consider. Using a bad iron may end up damaging the hair severely.






Among many types of straighteners, flat irons are the best ones. They may be a little expensive compared to other types but are the best in terms of safety. When you are shopping for one, try to pick a straightener that comes with ceramic coating. This type of product is gentle for hair and provides hair with extra shine and health.






Personal image, as it relates to external beauty, has attracted much attention from the cosmetic industry, and capillary aesthetics is a leader in consumption in this area. There is a great diversity of products targeting both the treatment and beautification of hair. Among them, hair straighteners stand out with a high demand by costumers aiming at beauty, social acceptance and ease of daily hair maintenance. However, this kind of treatment affects the chemical structure of keratin and of the hair fibre, bringing up some safety concerns. Moreover, the development of hair is a dynamic and cyclic process, where the duration of growth cycles depends not only on where hair grows, but also on issues such as the individual's age, dietary habits and hormonal factors. Thus, although hair fibres are composed of dead epidermal cells, when they emerge from the scalp, there is a huge variation in natural wave and the response to hair cosmetics. Although it is possible to give the hair a cosmetically favourable appearance through the use of cosmetic products, for good results in any hair treatment, it is essential to understand the mechanisms of the process. Important information, such as the composition and structure of the hair fibres, and the composition of products and techniques available for hair straightening, must be taken into account so that the straightening process can be designed appropriately, avoiding undesirable side effects for hair fibre and for health. This review aims to address the morphology, chemical composition and molecular structure of hair fibres, as well as the products and techniques used for chemical hair relaxing, their potential risk to hair fibre and to health and the legal aspects of their use.






Attempts at beautification, mainly in women, especially involve the skin and its annexes 1. Personal image, as it relates to external beauty, has been the target of investment in the beauty industry, and in this context, the branch of capillary aesthetics has attracted much attention from the cosmetic industry because it is considered a leader in consumption in this area 2. As hair is one of the few physical features that can be easily modified to create a totally different style, be it in length, colour, or shape 3, there is a great diversity of products targeted for both the treatment and the beautification of hair; among them, hair relaxers and straighteners stand out. Generally, the term ‘relaxer’ refers to products intended for the treatment of kinky hair, while ‘straightener’ refers to products used for the treatment of curly hair – in this work, the term ‘straightener’ is used when referring to both products. The reasons for the use of hair dryer include beauty, social acceptance and ease of daily hair maintenance 1. However, these cosmetics affect only the hair shaft. As the newly developing hair will not be affected by these alterations, the new emerging hair will grow with its natural, original shape, and therefore, hair straightening needs to be repeated every 4–6 weeks 3. Thus, the emphasis in this cosmetic treatment should be only on new growth, as repeated treatments can lead to hair breakage 3, and scalp and hair disorders 4, among others 1, 4-6. Moreover, although the hair fibres are composed of dead epidermal cells, when they emerge from the scalp, there is huge variation in natural wave and the response to hair cosmetics 5. Consequently, for obtaining good results, it is essential to understand the mechanism of the process and other important information such as the composition of natural hair fibres, the composition of products and techniques available for hair straightening. Thus, this review aims to address a comprehensive summary of the morphology, chemical composition and molecular structure of hair fibres, as well as the products and techniques used for chemical hair straightening, their potential risk to hair fibre and to health and legal aspects of their use.



What is a Seamless Steel Pipe?


Seamless steel pipes are perforated from whole round steel, and steel pipes without welds on the surface are called seamless steel pipes. According to the production method, seamless steel pipes can be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and top pipes. According to the cross-sectional shape, seamless steel pipes are divided into two types: round and special-shaped. Special-shaped pipes include square, oval, triangular, hexagonal, melon seed, star, and finned pipes. The maximum diameter is 900mm and the minimum diameter is 4mm. According to different purposes, there are thick-walled seamless steel pipes and thin-walled seamless steel pipes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemical industry, boiler pipes, bearing pipes, and high-precision structural steel pipes for automobiles, tractors, and aviation.






API seamless pipe have a hollow section and are used in large quantities as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, steel pipe is lighter in flexural and torsional strength and is an economical section steel. Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. Steel pipes are used to make ring parts, which can improve material utilization, simplify manufacturing procedures, and save materials and processing. Working hours.






A seamless steel pipe is a circular pipe having a hollow section and no seams around it. The ASTM seamless pipe is made of carbon steel, alloy steel, stainless steel ingot or solid tube blank, and then is made by hot rolling, cold rolling or cold drawing. Seamless pipes are considered superior to welded pipes as they are built using monolithic steel billets, with intrinsic mechanical strength, without seam welds.






What is a seamless steel pipe?


A seamless steel pipe is a circular pipe having a hollow section and no seams around it. The seamless steel pipe is made of carbon steel, alloy steel, stainless steel ingot or solid tube blank, and then is made by hot rolling, cold rolling or cold drawing. Seamless pipes are considered superior to welded pipes as they are built using monolithic steel billets, with intrinsic mechanical strength, without seam welds.






Characteristics of seamless steel pipe


Seamless steel pipe for the use of engineering and construction is very widely, it is a hollow steel strip no seams, it is mainly used to transport liquids pipelines, different look and general steel,one of those heavy type steel, it has a strong resistance to corrosion, resistant to general corrosion.


Will not rust, this performance makes seamless steel tubes extend the life, the most important is that it is very clean and no toxins.


Compared with other plastic seamless steel pipe having strong mechanical resistance, impact regardless of how high a temperature is not interested in the use of seamless steel pipe, it is mounted and the other pipe is the same, can replace other piped water and other liquids. 






Since the industrial applications have become complex and evolved a lot, the piping products are also changing to stay in the race. Although there are many pipe processing techniques, the industry's most influential controversy between electrical resistance welded and spiral steel pipe. 






As they are produced, some seamless pipe types harden, so heat treatment after production is not needed. Others need thermal therapy. Consult the seamless pipe form specification you are considering to learn if heat treatment would be needed.







As alternatives today, ERW and seamless steel piping remain primarily due to historical beliefs.






Generally, since a weld seam was used, the welded pipe was deemed inherently weaker. This supposed design weakness was absent from the seamless pipe and was deemed safer. Although it is true that welded pipe has a seam that makes it technically weaker, manufacturing processes and quality assurance regimes have all advanced to the degree that when its tolerances are not exceeded, welded pipe can work as expected. While the obvious benefit is apparent, a criticism of seamless piping is that, compared to the more reliable thickness of steel sheets intended for welding, the rolling and stretching process creates an inconsistent wall thickness.






These perceptions are still expressed by the industry standards that regulate the production and specification of ERW and seamless steel pipes. For example, for many high-pressure, high-temperature applications in the oil & gas, power generation and pharmaceutical industries, seamless piping is needed. Welded piping (which is typically cheaper to manufacture and is more commonly available) is defined in all industries as long as the parameters noted in the relevant specification do not exceed the temperature, pressure and other service variables.






There's no difference in efficiency between ERW and pile pipe in structural applications. Although the two can be interchangeably defined, since cheaper welded pipe works just as well, it does not make sense to specify for seamless.






Healthy welded and seamless steel pipe buying procedure


As piping products are listed for a project, an important note to be made is that the specification books (such as those supplied by ASTM, ASME, ANSI and API, among others) that engineers use to direct the specifications they write only list pipe grades exclusive of referencing whether they are generated through ERW or seamless pipe production. By both ways, not all grades can be made.






For example, if an engineer defines welded pipes with a wide outside diameter and wall thickness without understanding that it would be difficult to produce them, a potential mix-up could occur. Until a purchase order is placed, this mistake would possibly go unnoticed, at which point an industrial pipe supplier would tell the customer that the order could not be fulfilled as written. See us at International Pipe Suppliers for the supply.






The development of numerical simulations is potentially useful in predicting the most suitable manufacturing processes and ultimately improving product quality. Seamless pipes are manufactured by a rotary piercing process in which round billets (workpiece) are fed between two rolls and pierced by a stationary plug. During this process, the material undergoes severe deformation which renders it impractical to be modelled and analysed with conventional finite element methods. In this paper, three-dimensional numerical simulations of the piercing process are performed with an arbitrary Lagrangian–Eulerian (ALE) formulation in LS-DYNA software. Details about the material model as well as the elements’ formulations are elaborated here, and mesh sensitivity analysis was performed. The results of the numerical simulations are in good agreement with experimental data found in the literature and the validity of the analysis method is confirmed. The effects of varying workpiece velocity, process temperature, and wall thickness on the maximum stress levels of the product material/pipes are investigated by performing simulations of sixty scenarios. Three-dimensional surface plots are generated which can be utilized to predict the maximum stress value at any given combination of the three parameters.






Metal pipes are categorized into welded pipes and seamless pipes. Welded pipes are commonly manufactured by bending and welding metal sheets, while seamless pipes are produced using the rotary piercing process. It is well recognized that seamless pipe provides more benefits than welded pipe, such as (1) increased pressure ratings; (2) uniformity of geometry, material properties, and matter; and (3) structural strength and fatigue capacities under load. Offshore industry especially requires over 30–40 years of design life and robust design of the piping system, pipeline, and riser structures are requested by adopting reliable materials, manufacturing processes, installation, and operation. Many benefits of seamless pipe, i.e., uniformity of shape and fatigue and strength capacity, allow for higher safety during the operation period of offshore pipeline [1,2,3] and riser structures [4,5,6] from repeated environmental loadings [7,8].


In the rotary piercing process, a heated round billet is fed into a plug by the action of two skewed rolls which rotate in the same direction. The rolls are tilted and placed on opposite sides of the workpiece, providing both rotation and translation to the workpiece. As mentioned by Komori [9], the rolls can be barrel-shaped or cone-shaped. Since the invention of the piercing process over a century ago, numerous empirical and analytical studies have been conducted and one of the good reviews have been conducted by Komori and Mizuno [10]. Experimental studies on cone-shaped-type rotary piercing using lead and wax were performed and a comparison was drawn between two-roll and three-roll cone systems. It was shown that the three-roll cone systems are superior to that of two-roll systems by Khudeyer et al. [11]. The effects of varying the feed angle on the shear strain were studied experimentally using hot steel. Hayashi and Yamakawa [12] found that with larger cross angles, the decrease in the circumferential shear strain is more significant. Moon et al. [13] and Sutcliffe and Rayner [14] conducted experimental work on the rolling process using modelling clay (Plasticine) due to the similarities of its stress–strain behaviour with that of metals and because of its malleability and low cost.


Finite element analysis (FEA) of metal forming processes was further performed to gather the necessary information to design and control these processes properly. In addition, the number of experimental trials can be minimized through the exploitation of FEA, which would significantly reduce the product development lead time. Moreover, with the decrease of experimental work, the overall development cost of the product would be reduced. Nowadays, the advancement of powerful computer technology enables the numerical simulations to consider various physical phenomena during metal processing which include deformation, heat transfer, phase transformation, and ductile fracture [15,16,17].


A two-dimensional rigid-plastic finite element simulation of rotary piercing was performed by Mori et al. [18]. However, the accuracy of the results was low since generalized plane strain was assumed from the simulation. Three-dimensional rigid-plastic finite element analysis was performed by Komori [9]. The number of the elements was limited, and the mesh was relatively coarse because large amounts of computational time were required. Berazategui et al. [19] used the pseudo-concentrations technique to conduct three-dimensional rigid-viscoplastic finite element simulations and a new algorithm was proposed to describe the contact boundary conditions between the tools and the blank. The algorithm was validated with industrial tests of the barrel-type rotary piercing process. However, the numerical analysis of the process was found to be complicated and the computational cost was rather large. Thus, an alternative simplified method was highly required [10]. Shim et al. [20] used a rigid-thermo-viscoplastic finite element method and conducted simulations with AFDEX 3D software to predict the final shape in better detail. Intelligent re-meshing and tetrahedral elements were used which resulted in increased computational cost. The same method was then used to conduct numerical studies on the Mannesmann effect in the piercing process, as well as to compare between the Diescher’s guiding disk and Stiefel’s guiding shoe [21,22].


Lee et al. [23] presented a novel method for adaptive tetrahedral element generation for precision simulation of moving boundary problems such as bulk metal forming. The effects of using tetrahedral solid elements were investigated in a three-dimensional simulation of the forging process with an AFDEX 3D forging simulator. The predictions of both tetrahedral and standard hexahedral elements were in good agreement with experimental data provided that the remeshing technique is employed by Lee et al. [24]. Pater and Kazanacki [25] used Simufact Forming software to analyze the effects of the plug diameter, plug advance, and feed angle on the piercing process. The influence of different plug shapes was further investigated by Skripalenko et al. [26]. ProCAST and QForm commercial software were used for the numerical simulation of piercing aluminium alloy. Jung et al. [27] conducted 3D numerical simulations on the elongation rolling process to study how the rolling speed (rpm) and distance of guide shoes influenced the outer diameter and thickness of the pipe. MSC-SuperForm software was used and an automatic re-meshing method of hexagonal elements was implemented. Xiong et al. [28] used the reproducing kernel particle method for the steady and non-steady analysis of bulk-forming processes and validated the numerical predictions with experimental measurements. Topa and Shah [29] performed 3D numerical simulations for a forging process with a complex tool geometry using the smooth particle hydrodynamics (SPH) method. The results were in fair agreement with experimental data, but the method had a poor visual representation of the final geometry. Hah and Youn [30] presented an effective Eulerian approach for bulk metal forming based on representing boundaries as non-uniform rational B-spline (NURBS) and the effectiveness of the proposed approach was demonstrated by comparing with other numerical methods. However, this approach had the drawback of a blurred boundary condition imposition.






The tools are assumed to be rigid parts as their deformation is insignificant and out of the scope in the current study. They are modelled with shell elements to minimize computational cost. Material model 24 (Piecewise Linear Plasticity) was used to model the Plasticine material behaviour. In this model, the stress–strain curve of the material can be imported to the keyword file to define the relationship between stress and strain. Multiple curves at different strain rates can be used to take into consideration the strain rates’ effects via the stress yield scaling method. Large deformation will cause an increase in the temperature and thermal softening. However, due to the high velocity of the process, it was assumed that changes to temperature were minimal and there was insufficient time for heat transfer to occur between the workpiece and the tools. Thus, the process is simplified to an isothermal system.