OLEFIN FIBERS


Olefin fibers, also called polyolefin fibers, are defined as manufactured fibers in which the fiber-forming substance is a synthetic  polymer of at least 85 wt% ethylene, propylene, or other olefin units (1). Several olefin polymers are capable of forming fibers, but only polypropylene [9003-07-0] (PP) and, to a much lesser extent, polyethylene [9002-88-4] (PE) are of practical importance. Olefin polymers are hydrophobic and resistant to most solvents. These properties impart resistance to staining but cause the polymers to be essentially undyeable in an unmodified form.

The first commercial application of olefin fibers was for automobile seat covers in the late 1940s. These fibers, made from low density polyethylene (LDPE) by melt extrusion, were not very successful. They lacked dimensional stability, abrasion resistance, resilience, and light stability. The success of olefin fibers began when high density polyethylene (HDPE) was introduced in the late 1950s. Yarns made from this highly crystalline, linear polyethylene have higher tenacity than yarns made from the less crystalline. Markets were developed for HDPE fiber in marine rope where water resistance and buoyancy are important. However, the fibers also possess a low melting point, lack resilience, and have poor light stability. These traits caused the polyethylene fibers to have limited applications.

Isotactic polypropylene, based on the stereospecific polymerization catalysts discovered by Ziegler and Natta,was introduced commercially in the United States in 1957. Commercial polypropylene fibers followed in 1961. The first market of significance, contract carpet, was based on a three-ply, crimper-textured yarn. It competed favorably against wool and rayon–wool blends because of its lighter  weight, longer wear, and lower cost. In the mid-1960s, the discovery of improved light stabilizers led to the development of outdoor carpeting based on polypropylene.

In 1967, woven carpet backing based on a film warp and fine-filament fill was produced. In the early 1970s, a bulked-continuous-filament (BCF) yarn was introduced for woven, texturized upholstery. In the mid-1970s, further improvement in light stabilization of polypropylene led to a staple product for automotive interiors and nonwoven velours for floor and wall carpet tiles. In the early 1980s, polypropylene was introduced as a fine-filament staple for thermal bonded nonwovens.

The growth of polyolefin fibers continues. Advances in olefin polymerization provide a wide range of polymer properties to the fiber producer. Inroads into new markets are being made through improvements in stabilization, and new and improved methods of extrusion and production, including multicomponent extrusion and spunbonded and meltblown nonwovens.

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Olefin Fibers

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Production of Poly Ethylene Terephthalate


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PET is a polymer that possesses great importance in the contemporary world of plastics. Being a thermoplastic i.e. recyclable polymer made it the number one choice for numerous applications which satisfies the world need for a greener and more ecological alternative to commonly used plastics such as polyethylene and others.

Nowadays, Two PET grades dominate the global market fiber-grade PET and bottle-grade PET. They differ mainly in the end product properties such as optical appearance and production technologies where these properties can be controlled by molecular weight, intrinsic viscosity, and additives specific to each process or application. Other uses include film production and specialty nylons [17].

The scope of this report will focus on bottle-grade PET because of its high demand especially in the Egyptian market. The report discusses the historical development of PET, its importance, properties and material handling considerations.

Ever since its discovery in the beginning of 20th century several companies were interested n providing production technologies to supply the increasing need for large amounts of PET. Technologies and their current licensors are discussed in detail with their flow sheets, chemistry and specific properties.

The report splits the PET production processes into two main parts; monomer preparation and polymerization. Each of the technologies uses different raw materials, solvents, catalysts and reaction conditions with their advantages and disadvantages. After the detailed market study which has put into account both global and local markets’ considerations, a thorough evaluation study is constructed in the report to evaluate each technology according to standard evaluation techniques displayed in the evaluation section.

The carefully studied numbers and statistics in the market section led us to suggest a suitable capacity for the PET production plant based on many factors listed in the same place. The summation of the work done in this project is shown in the recommendation part where a justified process is selected to produce PET and TPA in Egypt. Further desired information about the report as a whole and any given part is attached to this report in the form of an appendix where much more detailed data can be found.

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PET-Production-Technical-Report

Essential Requirements of Fiber Forming Polymers


Both natural and man-made fibres are mainly composed of the compounds belonging to high polymers or macromolecules. Macromolecular structure is necessary for the production of materials of high mechanical strength and high melting point. The natural fibres are found to consist chain molecules of linear molecular type. Further, the chain molecules are oriented into the parallel bundles in the process of growth. Based on these investigations, it is assumed that polymers must satisfy the minimum requirements, if it is to serve as a fibre. These requirements are as mentioned follows:

· Flexibility

The polymer must be linear flexible macromolecule with a high degree of symmetry the effect of cross sectional diameter should be less than 15Å. The polymer should not contain any bulky side groups or chains.

· Molecular Mass

The polymer mass must have a comparatively high molecular mass. The average length of its molecular chain should be in order of 1000 Å or more.

· Configuration

The molecule must have the capacity to adopt an extended an extended configuration and state of mutual alignment.

· Crystallinity

A polymer should have at least a high degree of intermolecular cohesive power. This indicates that the molecular chains should have sufficient number of sites of attraction

· Orientation

A high degree of orientation of the molecules in the polymer is a pre-requisite for producing good tensile strength.

Polymerisation


The term polymerisation defines the process of macromolecules formation through repetition of basic units: it of course applies only to synthesis fibres. In general, polymerisation reactions are activated and controlled during the process by various parameters, as temperature, pressure, catalysers, reaction stabilizers.

The number of repetitive units is termed degree of polymerisation and is a parameter of great significance for fibre properties setting. As the length of the single molecules is not constant, but varies according to a statistical model, the degree of polymerisation or the correspondent molecular weight has to be considered as an average value.

Depending on the various fibre typologies, the degrees of polymerisation may range from some hundred units in the case of polymers obtained through condensation (PA, PES) to some thousand units in the case of polymers resulting from poly-addition (PAN, PP). Under a production and application point of view, the degree of polymerisation is controlled by measuring following parameters:

Relative viscosity ηrel= solution viscosity/solvent viscosity = flow time t1/flow time t2

Intrinsic viscosity ηintr= ηrel /c →0 (concentration vanishing)

Melt flow index MFI = speed rate of the melted polymer at pre-established conditions

Relative viscosity is a parameter which is mostly used to identify nylon, while intrinsic viscosity (obtainable from the relative viscosity also by means of formulas) is used for polyester and the melt flow index for polypropylene. There are basically two mechanisms of chemical reaction available for the synthesis of linear polymers:

Poly-condensation: with this operation two molecules of same type or of different types are joined together to form macromolecules by removing simple secondary products as water, hydrochloric acid, alcohol.

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Fig:- Polycondensation

The prerequisite for reactions of this type is the presence in the molecule (monomer) of two terminal reactive groups with functional properties. The molecules composed of 2,3,4…n monomers are named dimers, trimers, tetramers (oligomers)…polymers.

Some of the mostly used monomers are:

Aliphatic di-acids HOOC-R-COOH (used for nylon 6.6)

Aliphatic di-amines NH2-R-NH2 (used for nylon 6.6)

Aliphatic amino acids H2N-R-COOH (used for nylon 6)

Aromatic di-acids HOOC-Ar-COOH (used for polyester)

Diols (bi-functional alcohols) HO-R-OH (used for polyester)

Thus formed polymeric chains contain, besides carbon atoms, also various atoms (etero-atoms) resulting from the condensation reaction of the functional groups (e.g. nitrogen for polyamides, oxygen for polyester).

b) Poly-addition: this operation joins together several molecules and redistributes the valence links existing in the monomers, however without removing secondary products.

Many unsaturated compounds which are characterized by the presence of a double link between two adjacent carbon atoms as ethylene and its derivatives, polymerise according to this reaction; within this category fall e.g. acrylic and polyolefin fibres.

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FIG: Poly-addition

Among the most used polymers there are ethylene derived molecules with one or more

substitutes of hydrogen atoms.

For example:CH2=CHX

Where X=H,CH3,Cl,CN,OH and other groups.

The chains which are thus formed originate from simple openings of double ethylene links and are therefore characterized by links only among carbon atoms.

Difference between addition and condensation polymerisation processes

Through poly-addition not only secondary substances are removed: reactions follow a chain

process, are quicker, highly exothermic and usually require lower temperatures.

Molecular weights (degree of polymerisation) are higher and it is more likely to have chains

with cross or branched links.

Polymerisation, once it is completed, does not leave behind polymers of intermediate length

(oligomers), but only non-reacted products (monomers).

Poly-condensation, on the contrary, is a process in several stages which leaves behind, among

reaction products, also polymers with low molecular weight (oligomers).

Polymerisation techniques

From a processing point of view, the polymerisation can be carried out by mass treatment, solution or dispersion (suspension, emulsion). From the engineering point of view, the process can be:

• discontinuous, where reagents are entirely pre-loaded into the reactor and, as soon as the polymerisation is completed, the products are completely unloaded. The “batch” technique is used in particular for the production of small lots or of specialty items.

• continuous, where reagents are introduced from one end and reaction products come out from the other (this process is used especially for large productions). The reaction can also take place within a stationary phase (as typical for poly-additions) or at subsequent stages (as in poly-condensations).

Whichever polymerisation method is applied, the reaction products (polymers) can appear as follows:

• in form of a solution to be conveyed to the spinning department;

• in form of a melted polymer to be conveyed directly to the spinning department or to be transformed into grains (chips) for subsequent use ;

• in form of a suspension, from which the polymer is separated and conveyed to the spinning department;

Along with the chemical reactants (monomers and possible catalysts) during the polymerisation stage or anyway in a stage preceding spinning, other additives can be added in order to provide the fibre with certain properties: a product of particular importance is a white dulling agent (titanium dioxide in grains), which is added in small quantities in order to give the fibres a “dull” appearance, which distinguishes them from the untreated fibres which, owing to their brighter and “synthetic” appearance, are named “bright”. Under this point of view, the fibre is termed on the basis of the added quantity of titanium dioxide (dullness degree) as follows:

• bright fibre: a fibre without or with minimal quantities of titanium dioxide;

• semi-bright fibre: a slightly delustred fibre

• semi-dull fibre: usually terms delustred fibres with 0,25-0.5% titanium dioxide contents

• dull fibre: fibre with 0,5-1% titanium dioxide

• superdull fibre: fibre with 1-3% titanium dioxide

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Textile Fibers


Fibers -units of matter characterized by flexibility, fineness and high ratio of length to thickness. Other necessary attribute for textiles are adequate strength and resistance to conditions encountered during wears, as well as absence of undesirable colour, and finally the property of dye ability.

In generally, the steps in the manufacture of fabrics from raw material to finished goods are as follows:
· Fibre, which is either spun (or twisted) into yarn or else directly compressed into fabric.
· Yarn, which is woven, knitted, or otherwise made into fabric.
· Fabric, which by various dyeing and finishing processed becomes consumers goods.

  • Classification of textile fibers 

According to the nature and origin different textile fibers can be classified as follows:

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Natural fibers include those produced by plants, animals, and geological processes. They are biodegradable over time. They can be classified according to their origin:

  • Vegetable fibers are generally based on arrangements of cellulose, often with lignin: examples include cotton, hemp, jute, flax, ramie, and sisal.
  • Animal fibers consist largely of particular proteins. Instances are spider silk, sinew, catgut, wool and hair such as cashmere, mohair and angora, fur such as sheepskin, rabbit, mink, fox, beaver, etc.
  • Mineral fibers comprise asbestos. Asbestos is the only naturally occurring long mineral fiber. Short, fiber-like minerals include wollastinite, attapulgite and halloysite
  • Manmade fibers
Manmade fibers include those produced by reacting chemicals. They are non biodegradable. They can be classified according to their origin there are two sorts of man-made fibers: Organic and Inorganic.(a). Organic fibersSyntheticor man-made fibers generally come from synthetic materials such as petrochemicals.

  1.  Polymer fibers

Polymer fibers are a subset of man-made fibers, which are based on synthetic chemicals (often from petrochemical sources) rather than arising from natural materials by a purely physical process. Such fibers are made from:
o polyamide nylon,

o PET or PBT polyester

o phenol-formaldehyde (PF)

o polyvinyl alcohol fiber (PVOH)

o polyvinyl chloride fiber (PVC)

o polyolefins (PP and PE)

o acrylic polymers, pure polyacrylonitrile PAN fibers are used to make carbon fiber by roasting them in a low oxygen environment. Traditional acrylic fiber is used more often as a synthetic replacement for wool. Carbon fibers and PF fibers are noted as two resin-based fibers that are not thermoplastic, most others can be melted.

o Aromatic polyamids (aramids) such as Twaron, Kevlar and Nomex thermally degrade at high temperatures and do not melt. These fibers have strong bonding between polymer chains

o polyethylene (PE), eventually with extremely long chains / HMPE (e.g. Dyneema or Spectra).

o Elastomers can even be used, e.g. spandex although urethane fibers are starting to replace spandex technology.

o polyurethane fiber

o Co-extruded fibers have two distinct polymers forming the fiber, usually as a core-sheath or side-by-side. Coated fibers exist such
as nickel-coated to provide static elimination, silver-coated to provide anti-bacterial properties and aluminum-coated to provide RF deflection for radar chaff. Radar chaff is actually a spool of continuous glass tow that has been aluminum coated. An aircraft-mounted high speed cutter chops it up as it spews from a moving aircraft to confuse radar signals.
2. Regunrated fibers

Regunrated fibers are the fibers produced from natural cellulose, including rayon, modal, and the more recently developed Lyocell. Cellulose-based fibers are of two types, regenerated or pure cellulose such as from the cupro-ammonium process and modified or derivitized cellulose such as the cellulose acetates.

(b). Inorganic fibers

  • Mineral fibers

o Glass fiber, made from specific glass, and optical fiber, made from purified natural quartz, are also man-made fibers that come from natural raw materials.

o Metallic fibers can be drawn from ductile metals such as copper, gold or silver and extruded or deposited from more brittle ones, such as nickel, aluminum or iron.

o Carbon fibers are often based on carbonised polymers, but the end product is pure carbon.

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