xviii Woodhead Publishing Series in Textiles 158 Braiding technology for textiles Y.Kvosev 159 Principles of colour appearance and measurement A.K.R.Choudhury
xviii Woodhead Publishing Series in Textiles 158 Braiding technology for textiles Y. Kyosev 159 Principles of colour appearance and measurement A. K. R. Choudhury
1 Introduction to composite nonwovens D.DAS,Indian Institute of Technology Delhi,India D0:10.1533/9780857097750.1 Abstract:This chapter gives an introduction to composite nonwovens. It begins with the definitions of composites and nonwovens and continues to discuss how these definitions are used to define composite nonwovens.It then classifies composite nonwovens according to the materials used or manufacturing processes employed for the creation of composite nonwovens. Each class of composite nonwoven is described and discussed with numerous practical examples.The chapter then proceeds to discuss the scope,markets and applications of composite nonwovens.The final section highlights the challenges and promises of composite nonwovens. Key words:composite,nonwoven,definition,classification,scope,market, application. 1.1 Introduction The term 'composite nonwoven'has an interesting etymology.Impressionis- tically,it appears to mean a category of nonwoven materials which is prepared by a combination of different nonwoven preforms or different nonwoven fabrics. In the past,the members of the nonwoven industry used the terms 'composite nonwoven'and 'nonwoven composite'sometimes synonymously and sometimes differently.Those who preferred to use them differently would mean composite nonwoven as a material combining nonwoven preforms or nonwoven fabrics with at least one other material such as yarn,cloth,knit,braid and film,and nonwoven composite as a material consisting of a resinous matrix reinforced by an embedded nonwoven fabric (Das et al.,2012).Though composite nonwovens prepared by various combinations of materials and processes are well established, the definition of composite nonwovens has been a topic of debate in the nonwoven and allied industries.In the following sections,the definitions of the term 'composite'and 'nonwoven'are given and how they are used to define the term composite nonwovens'is discussed. 1.1.1 Definitions of composite The term 'composite'comes from the Latin word compositus,which means 'put together'indicating something made by putting together different parts or materials.Nevertheless,the definition of the term 'composite'has been continued to be confusing to the members of the nonwoven and allied industries. 1 2014 Woodhead Publishing Limited
1 © 2014 Woodhead Publishing Limited 1 Introduction to composite nonwovens D. DAS, Indian Institute of Technology Delhi, India DOI: 10.1533/9780857097750.1 Abstract: This chapter gives an introduction to composite nonwovens. It begins with the defi nitions of composites and nonwovens and continues to discuss how these defi nitions are used to defi ne composite nonwovens. It then classifi es composite nonwovens according to the materials used or manufacturing processes employed for the creation of composite nonwovens. Each class of composite nonwoven is described and discussed with numerous practical examples. The chapter then proceeds to discuss the scope, markets and applications of composite nonwovens. The fi nal section highlights the challenges and promises of composite nonwovens. Key words: composite, nonwoven, defi nition, classifi cation, scope, market, application. 1.1Introduction The term ‘composite nonwoven’ has an interesting etymology. Impressionistically, it appears to mean a category of nonwoven materials which is prepared by a combination of different nonwoven preforms or different nonwoven fabrics. In the past, the members of the nonwoven industry used the terms ‘composite nonwoven’ and ‘nonwoven composite’ sometimes synonymously and sometimes differently. Those who preferred to use them differently would mean composite nonwoven as a material combining nonwoven preforms or nonwoven fabrics with at least one other material such as yarn, cloth, knit, braid and fi lm, and nonwoven composite as a material consisting of a resinous matrix reinforced by an embedded nonwoven fabric (Das et al. , 2012). Though composite nonwovens prepared by various combinations of materials and processes are well established, the defi nition of composite nonwovens has been a topic of debate in the nonwoven and allied industries. In the following sections, the defi nitions of the term ‘composite’ and ‘nonwoven’ are given and how they are used to defi ne the term ‘composite nonwovens’ is discussed. 1.1.1Defi nitions of composite The term ‘composite’ comes from the Latin word compositus , which means ‘put together’ indicating something made by putting together different parts or materials. Nevertheless, the defi nition of the term ‘composite’ has been continued to be confusing to the members of the nonwoven and allied industries
n Composite Nonwoven Materials Holliday (1990)suggested a definition of composite for the nonwoven industry as a material comprising two or more different parts or elements in which each material has its own unique characteristics.These materials may include fibre, fabric,plastics,superabsorbents or other materials that effect and become a homogeneous part of,and are nonseparable from,the total structure Holliday made an attempt to differentiate composites from laminates by stating that a laminate is a material which is formed by uniting or bonding two or more distant layers that may be similar or different in composition,with heat,adhesive or pressure.These layers may include fabrics,foam,sheets,webs or films such that each layer retains a substantial portion of its original characteristics and therefore does not become homogeneous in the structure.Further,a laminate can be theoretically delaminated,i.e.the layers can be separated from one another. The North American Association of the Nonwoven Fabrics Industry (INDA) and the European Disposables and Nonwovens Association (EDANA)(2005) jointly define a composite material as a macroscopic combination of two or more distinct materials,having a recognizable interface between them.This definition of composite has not been accepted by the allied industries,however.The textile industry,which is closely associated with the nonwoven industry,follows another definition of composite.As per the Textile Institute Textile Terms and Definitions, composite is defined as a product formed by intimately combining two or more discrete physical phases,usually a solid matrix and a fibrous material (McIntyre and Daniels,1995).The textile industry therefore thinks of composites as fibre- reinforced-composites only. The man-made fibre industry,which is closely associated with the nonwoven industry,follows a similar definition of composite.As per the dictionary of man- made fibres,composites are materials with plastics as matrix and high tenacity fibres or short fibres as reinforcement;without this reinforcement,plastics would be insufficiently rigid,solid and impact resistant (Koslowski,1998).Thus the man-made fibre industry thinks about composites as fibre-reinforced and plastic- matrix composites only.The polymer industry however typically follows another definition of composite.The Encyclopaedia of Polymer Science and Technology (Mark,1970)defines composites as combinations of materials differing in composition or form on a macroscopic scale in which all of the constituents in the composites retain their identities and do not dissolve or otherwise completely merge into each other. The composite industry uses a different definition of composite.As per the ASTM (Committee D-30 on Composite Materials)standard D3878-07,a composite material is defined as a substance consisting of two or more materials, insoluble in one another,which are combined to form a useful engineering material possessing certain properties not possessed by the constituents.Further, a composite material is inherently inhomogeneous on a microscopic scale,but can often be assumed to be homogeneous on a macroscopic scale for certain engineering applications.The constituents of a composite retain their identities:
2 Composite Nonwoven Materials Holliday (1990) suggested a defi nition of composite for the nonwoven industry as a material comprising two or more different parts or elements in which each material has its own unique characteristics. These materials may include fi bre, fabric, plastics, superabsorbents or other materials that effect and become a homogeneous part of, and are nonseparable from, the total structure. Holliday made an attempt to differentiate composites from laminates by stating that a laminate is a material which is formed by uniting or bonding two or more distant layers that may be similar or different in composition, with heat, adhesive or pressure. These layers may include fabrics, foam, sheets, webs or fi lms such that each layer retains a substantial portion of its original characteristics and therefore does not become homogeneous in the structure. Further, a laminate can be theoretically delaminated, i.e. the layers can be separated from one another. The North American Association of the Nonwoven Fabrics Industry (INDA) and the European Disposables and Nonwovens Association (EDANA) (2005) jointly defi ne a composite material as a macroscopic combination of two or more distinct materials, having a recognizable interface between them. This defi nition of composite has not been accepted by the allied industries, however. The textile industry, which is closely associated with the nonwoven industry, follows another defi nition of composite. As per the Textile Institute Textile Terms and Defi nitions, composite is defi ned as a product formed by intimately combining two or more discrete physical phases, usually a solid matrix and a fi brous material (McIntyre and Daniels, 1995). The textile industry therefore thinks of composites as fi brereinforced-composites only. The man- made fi bre industry, which is closely associated with the nonwoven industry, follows a similar defi nition of composite. As per the dictionary of manmade fi bres, composites are materials with plastics as matrix and high tenacity fi bres or short fi bres as reinforcement; without this reinforcement, plastics would be insuffi ciently rigid, solid and impact resistant (Koslowski, 1998). Thus the man- made fi bre industry thinks about composites as fi bre- reinforced and plasticmatrix composites only. The polymer industry however typically follows another defi nition of composite. The Encyclopaedia of Polymer Science and Technology (Mark, 1970) defi nes composites as combinations of materials differing in composition or form on a macroscopic scale in which all of the constituents in the composites retain their identities and do not dissolve or otherwise completely merge into each other. The composite industry uses a different defi nition of composite. As per the ASTM (Committee D-30 on Composite Materials) standard D3878–07, a composite material is defi ned as a substance consisting of two or more materials, insoluble in one another, which are combined to form a useful engineering material possessing certain properties not possessed by the constituents. Further, a composite material is inherently inhomogeneous on a microscopic scale, but can often be assumed to be homogeneous on a macroscopic scale for certain engineering applications. The constituents of a composite retain their identities:
Introduction to composite nonwovens 3 they do not dissolve or otherwise merge completely into each other,although they act in concert. Each industry thus follows its own definition of composites.It appears that each of these industries have different circumstances and motivations so it is no wonder that they have pushed their own criteria for defining composites. 1.1.2 Definitions of nonwoven The definition of nonwoven has had an interesting history.A chronological description of the definitions of nonwoven has been given by Batra and Pourdeyhimi(2012).It can be observed that nonwoven has been defined differently from time to time by different authors,standardization agencies and industry associations.Nevertheless,the following definitions of nonwoven are generally found acceptable worldwide.As per ISO 9092,nonwoven is defined as: a manufactured sheet,web or batt of directionally or randomly oriented fibres,bonded by friction,and/or cohesion and/or adhesion,excluding paper and products which are woven,knitted,tufted,stitch-bonded incorporating binding yarns or filaments or felted by wet-milling,whether or not additionally needled.The fibres may be of natural or man-made origin.They may be staple or continuous filaments or be formed in situ.Note that the wet-laid nonwovens are distinguished from the wet-laid papers by a clause that a material shall be regarded as a nonwoven if more than 50%by mass of its fibrous content is made up of fibres (excluding chemically digested vegetable fibres)with a length to diameter ratio greater than 300;else if more than 30%by mass of its fibrous content is made up of fibres (excluding chemically digested vegetable fibres)with a length to diameter ratio greater than 300 and its density is less than 0.40g/cm'. This definition of nonwoven by ISO 9092 has been adapted by CEN(EN 29092) and consequently by DIN,AFNOR,and all standardization offices in the EU. ASTM prefers to define nonwoven as 'a textile structure produced by bonding or interlocking of fibres,or both,accomplished by mechanical,chemical,thermal, or solvent means,and combinations thereof.Note that the term does not include paper,or fabrics which are woven,knitted,tufted,or those made by wool or other felting processes.'This definition is available in many ASTM standards including D123,D1117,D2646,D3786,D3787,D5684,D5732,D5733,D5734,D 5735,andD5736. There are currently two leading associations of nonwovens producers in the world,namely EDANA(the European Disposables and Nonwovens Association) and INDA(the North American Association of the Nonwoven Fabrics Industry). They have been the voice of the nonwoven industries in Europe and North America,respectively.Nonwovens are defined by them as well.Though EDANA has adopted the definition of nonwoven given by ISO 9092 or CEN 29092,INDA
Introduction to composite nonwovens 3 they do not dissolve or otherwise merge completely into each other, although they act in concert. Each industry thus follows its own defi nition of composites. It appears that each of these industries have different circumstances and motivations so it is no wonder that they have pushed their own criteria for defi ning composites. 1.1.2Defi nitions of nonwoven The defi nition of nonwoven has had an interesting history. A chronological description of the defi nitions of nonwoven has been given by Batra and Pourdeyhimi (2012). It can be observed that nonwoven has been defi ned differently from time to time by different authors, standardization agencies and industry associations. Nevertheless, the following defi nitions of nonwoven are generally found acceptable worldwide. As per ISO 9092, nonwoven is defi ned as: a manufactured sheet, web or batt of directionally or randomly oriented fi bres, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch- bonded incorporating binding yarns or fi laments or felted by wet- milling, whether or not additionally needled. The fi bres may be of natural or man- made origin. They may be staple or continuous fi laments or be formed in situ. Note that the wet- laid nonwovens are distinguished from the wet- laid papers by a clause that a material shall be regarded as a nonwoven if more than 50% by mass of its fi brous content is made up of fi bres (excluding chemically digested vegetable fi bres) with a length to diameter ratio greater than 300; else if more than 30% by mass of its fi brous content is made up of fi bres (excluding chemically digested vegetable fi bres) with a length to diameter ratio greater than 300 and its density is less than 0.40 g/cm 3 . This defi nition of nonwoven by ISO 9092 has been adapted by CEN (EN 29092) and consequently by DIN, AFNOR, and all standardization offi ces in the EU. ASTM prefers to defi ne nonwoven as ‘a textile structure produced by bonding or interlocking of fi bres, or both, accomplished by mechanical, chemical, thermal, or solvent means, and combinations thereof. Note that the term does not include paper, or fabrics which are woven, knitted, tufted, or those made by wool or other felting processes.’ This defi nition is available in many ASTM standards including D 123, D 1117, D 2646, D 3786, D 3787, D 5684, D 5732, D 5733, D 5734, D 5735, and D 5736. There are currently two leading associations of nonwovens producers in the world, namely EDANA (the European Disposables and Nonwovens Association) and INDA (the North American Association of the Nonwoven Fabrics Industry). They have been the voice of the nonwoven industries in Europe and North America, respectively. Nonwovens are defi ned by them as well. Though EDANA has adopted the defi nition of nonwoven given by ISO 9092 or CEN 29092, INDA
4 Composite Nonwoven Materials prefers to define nonwovens in another way.According to INDA,nonwoven fabrics are broadly defined as sheet or web structures bonded together by entangling fibre or filaments (and by perforating films)mechanically,thermally or chemically.They are flat and porous sheets that are made directly from separate fibres or from molten plastic or plastic film.They are not made by weaving or knitting and do not require converting the fibres to yarn.'It is quite interesting to note that everybody has their own definition of nonwoven and there is no unique definition of nonwovens existing in the world. 1.1.3 Definitions of composite nonwoven There are also definitions available for composite nonwovens.Bikales (1976) classified nonwoven fabrics into four categories: 1 fabrics produced by chemical and mechanical finish fabrics produced by wet processes using modified papermaking techniques 3 spunbonded fabrics 4 composite fabrics produced from laminates of scrims,fibres,or foams with tissue,films,or other nonwoven fabrics. An example of the fourth category of nonwoven fabric is as follows.Continuous- filament yarns were coated with a phenolic resin and converted into a cross-laid nonwoven scrim to which layers of tissue were applied to each side and finally the composite was exposed to heat to allow the adhesive to set.Holliday (1990)cited interesting examples of composite nonwovens as a combination of carded webs and other webs or fibrous materials by means of water jet entanglement,or a combination of webs,fabrics,yarns,scrims,foam and other materials,or a combination of a highloft of fibrefill nonwoven and a meltblown nonwoven such that the meltblown fibres are blown between the fibres of the fibrefill and penetrate into the structure.It was further added that a foam laminated nonwoven for making wipes and a needle-punched felt bonded to a film and embossed cannot be considered an example of composite nonwoven,but can be considered as an example of laminated nonwoven. The definition of composite nonwoven,as given by INDA/EDANA(2005),is widely discussed by the nonwoven industries worldwide.According to it,the term composite nonwoven is used when the essential part of a composite material can be identified as a nonwoven material;if the essential part cannot be identified,the term composite nonwoven is used when the mass of the nonwoven content is greater than the mass of any other component material.Further,EDANA added that a composite nonwoven may be an unbounded nonwoven preform to which filaments or spun yarns have been incorporated. However,there is a different description available for composite structure as given by Hutten(2007).According to him,for a medium to be fit for the definition of composite structure it must be layered.In this connection,he cited a few
4 Composite Nonwoven Materials prefers to defi ne nonwovens in another way. According to INDA, ‘nonwoven fabrics are broadly defi ned as sheet or web structures bonded together by entangling fi bre or fi laments (and by perforating fi lms) mechanically, thermally or chemically. They are fl at and porous sheets that are made directly from separate fi bres or from molten plastic or plastic fi lm. They are not made by weaving or knitting and do not require converting the fi bres to yarn.’ It is quite interesting to note that everybody has their own defi nition of nonwoven and there is no unique defi nition of nonwovens existing in the world. 1.1.3Defi nitions of composite nonwoven There are also defi nitions available for composite nonwovens. Bikales (1976) classifi ed nonwoven fabrics into four categories: 1 fabrics produced by chemical and mechanical fi nish 2 fabrics produced by wet processes using modifi ed papermaking techniques 3 spunbonded fabrics 4 composite fabrics produced from laminates of scrims, fi bres, or foams with tissue, fi lms, or other nonwoven fabrics. An example of the fourth category of nonwoven fabric is as follows. Continuous- fi lament yarns were coated with a phenolic resin and converted into a cross- laid nonwoven scrim to which layers of tissue were applied to each side and fi nally the composite was exposed to heat to allow the adhesive to set. Holliday (1990) cited interesting examples of composite nonwovens as a combination of carded webs and other webs or fi brous materials by means of water jet entanglement, or a combination of webs, fabrics, yarns, scrims, foam and other materials, or a combination of a highloft of fi brefi ll nonwoven and a meltblown nonwoven such that the meltblown fi bres are blown between the fi bres of the fi brefi ll and penetrate into the structure. It was further added that a foam laminated nonwoven for making wipes and a needle- punched felt bonded to a fi lm and embossed cannot be considered an example of composite nonwoven, but can be considered as an example of laminated nonwoven. The defi nition of composite nonwoven, as given by INDA/EDANA (2005), is widely discussed by the nonwoven industries worldwide. According to it, the term composite nonwoven is used when the essential part of a composite material can be identifi ed as a nonwoven material; if the essential part cannot be identifi ed, the term composite nonwoven is used when the mass of the nonwoven content is greater than the mass of any other component material. Further, EDANA added that a composite nonwoven may be an unbounded nonwoven preform to which fi laments or spun yarns have been incorporated. However, there is a different description available for composite structure as given by Hutten (2007). According to him, for a medium to be fi t for the defi nition of composite structure it must be layered. In this connection, he cited a few