CHAPTER 1
INTRODUCTION TO FOAM PRODUCTION
Foam can be defined as a soft light rubber, full of small holes, no matter how tiny they could be, that has a wide variety of application. Foam has become a very important material required for a vast production of so many other materials needed for the satisfaction of human want. These materials include; vehicle seat, mattresses and cushion to name but a few. Owing to the vast use and need for foams, there is now an increase in its production across the globe. Foam production can be said to be the process of manufacturing foam blocks by putting together some chemicals like polyol, Toluene Diisocynate and others in the right proportion with the right catalyst, which can be used in the manufacturing of some finished goods like mattresses, pillow, cushion and other foam materials.
1
There are various types of foam, which includes:
Polyurethane foam; Used for fill, packing, shipping, mattress topper, dog beds, costumes. Thick pieces will develop "sink" areas after a short time. Polyurethane foam is really not a high quality of foam, and will often not return to its original form. Most times, one cannot guarantee the foam will maintain its original shape during shipping.
High density foam; Sold primarily for mattresses, average sofa and chair cushions, baywindows, boats, camping pads, etc...
Evlon foam; Also known as Lux foam. A "good" foam, typically used for upper scale furniture seating and mattresses. It is very buoyant.
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There are various types of foam, which includes:
Polyurethane foam; Used for fill, packing, shipping, mattress topper, dog beds, costumes. Thick pieces will develop "sink" areas after a short time. Polyurethane foam is really not a high quality of foam, and will often not return to its original form. Most times, one cannot guarantee the foam will maintain its original shape during shipping.
High density foam; Sold primarily for mattresses, average sofa and chair cushions, baywindows, boats, camping pads, etc...
Evlon foam; Also known as Lux foam. A "good" foam, typically used for upper scale furniture seating and mattresses. It is very buoyant.
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High resilience foam; Used in most types of expensive furniture including yachting and boating. Makes for an excellent mattress, very buoyant and resilient.
Latex rubber foam; This is a non-allergenic, first type of foam on market, longest lasting. Used in top of the line products including mattresses, cushions etc... (Better than High Resilience)
Supreme foam; Used primarily for computer and camera cases, packing and shipping, acoustical dampening and sound proofing. It is charcoal grey/black in color.
Rebond foam; Used as carpet padding, weight equipment, outdoor furnishing and other covered padding. Widely used in the
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hospital. Has very high resiliency and stands up to high impact / usage.
Memory foam; Also known as NASA foam, miracle foam, wonder foam or viscolastic foam. Developed for space shuttle seating and used for mattresses and seating. Very dense, conforms to shape - most unique foam on the market today.
Closed cell Foam; Non-water absorbent, non-biodegradable, floats, great tensile strength, impervious to petroleum. Used in exercise mats, high impact aerobic equipment, mechanic's box lining (.25" to .50" thick). Good thermal insulator (hot tub covers).
Dry fast foam; Very good for outdoor uses, very resilient and buoyant, open cell structure. Used filtering, or padding that is subject to high amounts of liquid .
4
In all the foam types mentioned above, one thing is common and that is, that they all emanate from the polyurethanes. The difference in each and every one of them, is dependent on the nature of some other chemical elements added to it in other to give it the desirable quality.
Owning to their common relationship to polyurethanes, most companies have polyurethane foam as the basics for their production. Therefore, we will be going into the production process of a polyurethane foam.
5
CHAPTER 2
THEORY OF POLYURETHANE FOAM PRODUCTION Polyurethanes are linear polymers that have a molecular backbone containing carbamate groups (-NHCO2). These groups, called urethane, are produced through a chemical reaction between a diisocyanate and a polyol. First developed in late 1930s, polyurethanes are some of the most versatile polymers. They are used in vast foam production, building insulation, surface coatings, adhesives, solid plastics, and athletic apparel.
Polyurethanes, also known as polycarbamates, belong to a larger class
of
compounds
called
polymers.
Polymers
are
macromolecules made up of smaller, repeating units known as monomers. Generally, they consist of a primary long-chain backbone molecule with attached side groups. Polyurethanes are characterized by carbamate groups (-NHCO backbone.
6
2
) in their molecular
Synthetic polymers, like polyurethane, are produced by reacting monomers in a reaction vessel. In order to produce polyurethane, a step—also known as condensation—reaction is performed. In this type of chemical reaction, the monomers that are present contain reacting end groups. Specifically, a diisocyanate (OCN-RNCO) is reacted with a diol (HO-R-OH). The first step of this reaction results in the chemical linking of the two molecules leaving a reactive alcohol (OH) on one side and a reactive isocyanate (NCO) on the other. These groups react further with other monomers to form a larger, longer molecule. This is a rapid process which yields high molecular weight materials even at room
temperature.
Polyurethanes
that
have
important
commercial uses typically contain other functional groups in the molecule including esters, ethers, amides, or urea groups.
BRIEF HISTORY OF POLYURETHANE
Polyurethane chemistry was first studied by the German chemist, Friedrich Bayer in 1937. He produced early prototypes by reacting
7
toluene diisocyanate reacted with dihydric alcohols. From this work one of the first crystalline polyurethane fibers, Perlon U, was developed. The development of elastic polyurethanes began as a program to find a replacement for rubber during the days of World War II. In 1940, the first polyurethane elastomers were produced. These compounds gave millable gums that could be used as an adequate alternative to rubber. When scientists found that polyurethanes could be made into fine threads, they were combined with nylon to make more lightweight, stretchable garments.
In 1953, the first commercial production of a flexible polyurethane foam was begun in the United States. This material was useful for foam insulation. In 1956, more flexible, less expensive foams were introduced. During the late 1950s, moldable polyurethanes were produced. Over the years, improved polyurethane polymers have been developed including Spandex fibers, polyurethane coatings, and thermoplastic elastomers.
8
THE CHEMISTRY OF POLYURETHANE
Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters , and
phenolics. A urethane linkage is produced by reacting an
isocyanate group, -N=C=O with a hydroxyl (alcohol) group, -OH. Generalised polyurethane reaction
Polyurethanes are produced by the polyaddition reaction of a polyisocyanate with a polyalcohol (polyol) in the presence of a catalyst and other additives. In this case, a polyisocyanate is a molecule with two or more isocyanate functional groups, R(N=C=O)n ≥ 2 and a polyol is a molecule with two or more hydroxyl functional groups, R'-(OH)n ≥ 2. The reaction product is a polymer containing the urethane linkage, -RNHCOOR'-. Isocyanates will react with any molecule that contains an active hydrogen. Importantly, isocyanates react with water to form a urea linkage and carbon dioxide gas; they also react with polyetheramines to
9
form polyureas. Commercially, polyurethanes are produced by reacting a liquid isocyanate with a liquid blend of polyols, catalyst, and other additives. These two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'. This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'Aside' and 'B-side' are reversed. Resin blend additives may include chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers.
The first essential component of a polyurethane polymer is the isocyanate. Molecules that contain two isocyanate groups are called diisocyanates. These molecules are also referred to as monomers or monomer units, since they themselves are used to produce polymeric isocyanates that contain three or more isocyanate functional groups. Isocyanates can be classed as aromatic, such as diphenylmethane diisocyanate (MDI) or toluene
10
diisocyanate
(TDI);
or
aliphatic, such
as
hexamethylene
diisocyanate (HDI) or isophorone diisocyanate (IPDI). An example of a polymeric isocyanate is polymeric diphenylmethane diisocyanate, which is a blend of molecules with two-, three-, and four- or more isocyanate groups, with an average functionality of 2.7. Isocyanates can be further modified by partially reacting them with a polyol to form a prepolymer. A quasi-prepolymer is formed when the stoichiometric ratio of isocyanate to hydroxyl groups is greater than 2:1. A true prepolymer is formed when the stoichiometric ratio is equal to 2:1. Important characteristics of isocyanates are their molecular backbone, % NCO content, functionality, and viscosity.
The second essential component of a polyurethane polymer is the polyol. Molecules that contain two hydroxyl groups are called diols, those with three hydroxyl groups are called triols, et cetera. In practice, polyols are distinguished from short chain or lowmolecular weight glycol chain extenders and cross linkers such as ethylene glycol (EG), 1,4-butanediol (BDO), diethylene glycol
11
(DEG), glycerine, and trimethylolpropane (TMP). Polyols are polymers in their own right. They are formed by base-catalyzed addition of propylene oxide (PO), ethylene oxide (EO) onto a hydroxyl or amine containing initiator, or by polyesterification of a di-acid, such as adipic acid, with glycols, such as ethylene glycol or dipropylene glycol (DPG). Polyols extended with PO or EO are polyether polyols. Polyols formed by polyesterification are polyester polyols. The choice of initiator, extender, and molecular weight of the polyol greatly affect its physical state, and the physical properties of the polyurethane polymer. Important characteristics of polyols are their molecular backbone, initiator, molecular weight, % primary hydroxyl groups, functionality, and viscosity.
PU reaction mechanism catalyzed by a tertiary amine
12
carbon dioxide gas formed by reacting water and isocyanate
The polymerization reaction is catalyzed by tertiary amines, such as dimethylcyclohexylamine, and organometallic compounds, such as dibutyltin dilaurate or bismuth octanoate. Furthermore, catalysts can be chosen based on whether they favor the urethane (gel) reaction, such as 1,4-diazabicyclo[2.2.2]octane (also called DABCO or TEDA), or the urea (blow) reaction, such as bis-(2-
13
dimethylaminoethyl)ether, or specifically drive the isocyanate trimerization reaction, such as potassium octoate.
One of the most desirable attributes of polyurethanes is their ability to be turned into foam. Blowing agents such as water, certain
halocarbons
such
as
HFC-245fa
(1,1,1,3,3-
pentafluoropropane) and HFC-134a (1,1,1,2-tetrafluoroethane), and hydrocarbons such as n-pentane, can be incorporated into the poly side or added as an auxiliary stream. Water reacts with the isocyanate to create carbon dioxide gas, which fills and expands cells created during the mixing process. The reaction is a three step process. A water molecule reacts with an isocyanate group to form a carbamic acid. Carbamic acids are unstable, and decompose forming carbon dioxide and an amine. The amine reacts with more isocyanate to give a substituted urea. Water has a very low molecular weight, so even though the weight percent of water may be small, the molar proportion of water may be high and considerable amounts of urea produced. The urea is not very soluble in the reaction mixture and tends to form separate "hard
14
segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact
on
the
properties
of
the
polyurethane
foam.[11]
Halocarbons and hydrocarbons are chosen such that they have boiling points at or near room temperature. Since the polymerization reaction is exothermic, these blowing agents volatilize into a gas during the reaction process. They fill and expand the cellular polymer matrix, creating a foam. It is important to know that the blowing gas does not create the cells of a foam. Rather, foam cells are a result of blowing gas diffusing into bubbles that are nucleated or stirred into the system at the time of mixing. In fact, high-density microcellular foams can be formed without the addition of blowing agents by mechanically frothing or nucleating the polyol component prior to use.
Surfactants are used to modify the characteristics of the polymer during the foaming process. They are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and surface defects. Rigid foam surfactants are
15
designed to produce very fine cells and a very high closed cell content. Flexible foam surfactants are designed to stabilize the reaction mass while at the same time maximizing open cell content to prevent the foam from shrinking. The need for surfactant can be affected by choice of isocyanate, polyol, component compatibility, system reactivity, process conditions and equipment, tooling, part shape, and shot weight.
Though the properties of the polyurethane are determined mainly by the choice of polyol, the diisocyanate exerts some influence, and must be suited to the application. The cure rate is influenced by the functional group reactivity and the number of functional isocyanate groups. The mechanical properties are influenced by the functionality and the molecular shape. The choice of diisocyanate also affects the stability of the polyurethane upon exposure
to
light.
Polyurethanes
made
with
aromatic
diisocyanates yellow with exposure to light, whereas those made with aliphatic diisocyanates are stable.
16
Softer, elastic, and more flexible polyurethanes result when linear difunctional polyethylene glycol segments, commonly called polyether polyols, are used to create the urethane links. This strategy is used to make spandex elastomeric fibers and soft rubber parts, as well as foam rubber. More rigid products result if polyfunctional polyols are used, as these create a threedimensional cross-linked structure which, again, can be in the form of a low-density foam.
An even more rigid foam can be made with the use of specialty trimerization catalysts which create cyclic structures within the foam matrix, giving a harder, more thermally stable structure, designated as polyisocyanurate foams. Such properties are desired in rigid foam products used in the construction sector.
Careful control of viscoelastic properties — by modifying the catalysts and polyols used —can lead to memory foam, which is much softer at skin temperature than at room temperature.
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There are then two main foam variants: one in which most of the foam bubbles (cells) remain closed, and the gas(es) remains trapped, the other being systems which have mostly open cells, resulting after a critical stage in the foam-making process (if cells did not form, or became open too soon, foam would not be created). This is a vitally important process: if the flexible foams have closed cells, their softness is severely compromised, they become pneumatic in feel, rather than soft; so, generally speaking, flexible foams are required to be open-celled.
The opposite is the case with most rigid foams. Here, retention of the cell gas is desired since this gas (especially the fluorocarbons referred to above) gives the foams their key characteristic: high thermal insulation performance.
A third foam variant, called microcellular foam, yields the tough elastomeric materials typically experienced in the coverings of car steering wheels and other interior automotive components.
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RAW MATERIALS FOR POLYURETHANE FOAM PRODUCTION
In polyurethane foam production, various raw materials are required and this includes:
A compound with an isocyanate group.
A compound with an alcohol group.(polyol)
Additives o
Surfactants
o
Blowing agents
o
Flame retardant
o
Light retarders
o
Fillers.
Brief explanation of the major ones.
Isocyanates
Isocyanates with two or more functional groups are required for the formation of polyurethane polymers. Volume wise, aromatic isocyanates account for the vast majority of global diisocyanate production. Aliphatic and cycloaliphatic isocyanates are also
19
important building blocks for polyurethane materials, but in much smaller volumes. There are a number of reasons for this. First, the aromatically linked isocyanate group is much more reactive than the aliphatic one. Second, aromatic isocyanates are more economical to use. Aliphatic isocyanates are used only if special properties are required for the final product. For example, light stable coatings and elastomers can only be obtained with aliphatic isocyanates. Even within the same class of isocyanates, there is a significant difference in reactivity of the functional groups based on steric hindrance. In the case of 2,4-toluene diisocyanate, the isocyanate group in the para position to the methyl group is much more reactive than the isocyanate group in the ortho position.
The two most important aromatic isocyanates are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). TDI consists of a mixture of the 2,4- and 2,6-diisocyanatotoluene isomers.
Polyols
20
The other reacting species required to produce polyurethanes are compounds that contain multiple alcohol groups (OH), called polyols. Materials often used for this purpose are polyether polyols, which are polymers formed from cyclic ethers. They are typically produced through an alkylene oxide polymerization process. They are high molecular weight polymers that have a wide range of viscosity. Various polyether polyols that are used include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These materials are generally utilized when the desired polyurethane is going to be used to make flexible foams or thermoset elastomers.
Polyester polyols may also be used as a reacting species in the production of polyurethanes. They can be obtained as a byproduct of terephthalic acid production. They are typically based on saturated aromatic carboxylic acids and diols. Branched polyester polyols are used for polyurethane foams and coatings. Polyester polyols were the most used reacting species for the production of
21
polyurethanes. However, polyether polyols became significantly less expense and have supplanted polyester polyols.
Catalysts
Polyurethane catalysts can be classified into two broad categories, amine compounds and organometallic complexes. They can be further classified as to their specificity, balance, and relative power or efficiency.
Organometallic compounds based on mercury, lead, tin (dibutyltin dilaurate), bismuth (bismuth octanoate), and zinc are used as polyurethane catalysts.
Surfactants
Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In
22
foams, they are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and sub-surface voids. In non-foam applications they are used as air release and anti-foaming agents, as wetting agents, and are used to eliminate surface defects such as pin holes, orange peel, and sink marks.
SIGNIFICANCE OF VARIOUS CHEMICALS, ELEMENTS AND COMPOUNDS USED IN FOAM PRODUCTION.
Just as we said before, the following are the elements/chemicals and their significance; 1. TOULENE DIISOCYNATE (TDI); This is a major chemical used in foam production. It is a very toxic chemical and the most basic required for production. 2. POLYPROPYLENE GLYCOL (POLYOL); This is a major chemical needed also to dilute the toluene diisocyanate.
23
3. METHLY CHLORIDE; This is a colorless compound which is very cold to the touch. It acts as a blowing agent during production and also used in flushing the mixer head after production. it is also used in cleaning the trough after production.
4. SILICONE; This is used for stabilization and smoothening of the foam. 5. AMINE; This is used for curing. Curing is the ability of foam to dry easily. 6. COLORANT; This adds color to the foam. It could be blue or pink depending on what is needed. 7. Tin;
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This is acting as a binding agent in foam production. 8. WATER; This also aid in reducing the temperature of the process. It also helps in diluting the mixed chemicals.
FOAM PRODUCTION PROCESS.
For a foam block to be manufactured, there are some major steps or processes which must be undergone and they include:
1. Pumping of chemicals 2. Cooling of pumped chemicals 3. Injection and mixing of chemicals in the foam plant machine 4. Production and conveying 5. Cutting
1. Pumping of chemicals
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In the production of foam, there are three major chemicals used which are;
Polypropylene glycol(polyol)
Toluene Diisocynate(TDI)
Methyl chloride
Toluene Diisocynate is a very toxic chemical which can choke one to death while polypropylene is a chemical used to dilute toluene Diisocynate and it is not toxic. There are other elements and compounds which may serve as catalysts or that may add other qualities to foam and these chemical, elements and compounds include;
Zinc
Silicone
Colorants
Tin
Amine
Water
26
These various elements, compounds and chemicals have various useful effects on a foam block, but the various functions would be discussed later. Pumping of chemical is a process of filling the various chemical
tanks in the chemical room. This is done by passing the chemicals through separate pipes with the aid of a pump attached to each tank. Here, the major chemicals are concerned i.e. TDI, polyol and methyl chloride. The other elements and compounds are not kept in the chemical room rather, they are kept very close to the foam plant machine in a smaller container. 2. Cooling of chemical
The pumped chemicals are kept or stored in their various tanks in a chemical room which is more or less like a cool room. This is because a cooling machine has being attached to the room. This is very important, owing to the fact that a fire outbreak could occur, if the chemicals are heated up, most especially the Toluene
27
Diisocynate. To each of the tanks, is a pump attached to enhance injection and pumping of the chemicals. 3. Injection and mixing of the chemical in the foam plant machine
Injection is the process of transferring the amount of or percentage of feed or chemical needed for production from the chemical room to the foam plant machine. This injection is done by the means of a pipe which has a pump attached to it. After the injection, all the chemicals, elements and compounds needed for the production meet at a part of the foam plant machine known as the mixer head, where they all mix together. 4. Production and conveying
The production process is a continuous process. Hence, the chemicals enter the system which is more or less like a conveyor. There in the conveyor, the chemicals start rising while the conveyor conveys them. There is a rising distance and that is the distance at which a particular foam must have set. Here, the rising
28
point was between 95cm-98cm. This is continuous until the whole production has been done. 5. Cutting
At one part of the conveyor, few centimeters away from the rising point is an automated cutting machine which can also be manually operated .the cutter or blade cuts the long foam block in blocks of equal sizes to enhance carriage. As soon as cutting has been done, everything about production has finished. Finally, the work place is cleared and the mixer head is flushed with methyl chloride and the trough through which the chemicals go into the conveyor is cleaned efficiently with CH 3CL also, in order to remove any particle that must have glued to it in the course of the production. Then, the production room is left till the next day In order to allow all the toxic gases escape before the final arrangement.
29
The foam blocks are sent to the conversion unit in order to be converted to pillow, mattresses, cushion and so on. The diagrammatic representation of a foam production process flow diagram is as shown below.
polyol
Mixer head conveyor Output(foam)
TDI
MeCl H0
silicon
tin
colour amine zinc
pump
An industry that is also into rebond foam production, continues after the production of polyurethane by putting the foam block which have been cut into a foam bond machine. A foam bond machine contains an automated foam grinder, known as a crumb machine, which grinds foam blocks into smaller pieces and mixes them up with a gum like liquid as to enable them
30
bond with each other. Then the machine has a large compressing flat surface which compresses the foam pieces which are now in a container that has the desired shape. When the flat surface compresses the foam, they are bonded together into the desirable shape. Then you have the rebond foam widely known in this par t of the country as orthopedic foam. In an ideal foam production firm, there are three major units and they are: 1. The production unit 2. The conversion unit 3. The marketing unit Production unit
This is the unit in which the actual production of the foam block takes place. All the production machineries like the omega mass computerizing machine, bonded machine, grinders, pumps and chemical storage tanks are located.
31
The conversion unit
This is the next important unit after the production unit. Here the foam blocks produced are converted into mattresses, pillow and cushion. This unit comprises of an automated cutter and sewing machines. Here, the bare foam blocks are given beautiful and attractive coverings.
The marketing unit
This unit is also known as the sales unit. This unit is where finished goods are sold and marketed. The first to unit can be combined in one to give two major units. Foam production is quite amazing because of the way liquid chemicals rise into foam blocks.
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CHAPTER 3
APPARATUS AND PROCEDURE Apparatus used in foam production
This includes the machines, chemicals and elements used in foam production. They are;
Machines include
Rebond foam machine and crumb
Compressing machine
Omega mass computerizing machine or maxfoam machine
Charts
Chemicals and elements
Polypropylene glycol(polyol)
Toluene Diisocynate(TDI)
Methyl chloride
Zinc
Silicone
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Colorants
Tin
Amine
Water
PROCEDURES IN FOAM PRODUCTION
The steps involved for a successful foam production, is as shown below.
1. Pumping of chemicals
2. Cooling of pumped chemicals
3. Injection and mixing of chemicals in the foam plant machine
4. Production and conveying
5. Cutting
The above procedures have been discussed at length in the theory part of this piece of work.
34
CHAPTER 4
ANALYSIS OF THE FOAM PLANT MACHINE The machine used in Group enterprises is called Omega Computerizing machine. It can also be said to be a continuous foam plant machine due to the fact that the process is continuous (i.e. it keeps working until the last output is gotten). In the machine, other elements meet polyol at the mixer head. The mixer head has a motor that runs between 3500rpm4000rpm.The machine has a conveyor which has side papers to avoid running off of the mixed chemicals. A cutting blade is attached say at 100cm mark of the conveyor, which cuts the blocks into equal sizes. The trough is connected to the mixer head by the means of a pipe which supplies chemicals to the trough from where the chemical are poured into the conveyor.
35
As we said before, the machine is computerized. Hence, the various percentages needed for a given production is typed into the computer while the computer monitors the operation at a given conveyor speed and the mixer speed. All these could be seen on the screen of the monitor. The table of the process is shown on the monitor as shown on fig.1 of the appendix. The feeding process of the data into the system is a very meticulous process because any slight error or mistake can lead to the production of an undesirable foam block which automatically leads to loss and wastage of raw materials. This is the reason why there is percentage error in the diagram above. This a way through which the system corrects slight errors fed in to the system.
36
CONCLUSION Chemical engineering is all about process brought about by the application of mathematics, physics and chemistry, of which foam production underwent some processes before coming to a finished product. A chemical engineer is highly interested in the inputs, reactions going on in the system, the accumulation and several other processes going on within and without the system. Hence chemical engineer is more interested in the reactants, their reactions and the products formed. Owing to the nature of the interest of a chemical engineer, then the need for him in a foam manufacturing plant can never be over emphasized. This is because foam production, is all about the general reaction between a higher isocyanate group and an alcohol group.
A chemical engineer also performs the function of quality control in order to ensure a quality polyurethane foam. In order to
37
achieve this, he monitors the product during all phases of production. These inspections begin with an evaluation of the incoming raw materials by quality control chemists. They test various chemical and physical characteristics using established methods. Some of characteristics that are tested include the pH, specific
gravity,
appearance,
and
color,
viscosity
and
odour
or
thickness.
may
also
be
Additionally, examined.
Manufacturers have found that only by strictly controlling the quality at the start of production can they ensure that a consistent finished product will be achieved.
After
production,
the
polyurethane
product
is
tested.
Polyurethane coating products are evaluated in the same way the initial raw materials are checked. Also, characteristics like dry time, film thickness, and hardness are tested. Polyurethane fibres are tested for things such as elasticity, resilience, and absorbency. Polyurethane foams are checked to ensure they have the proper density, resistance, and flexibility.
38
In conclusion, a foam process plant is purely based on various chemical engineering processes, starting from the pumping of the chemicals, to the mixing and finally the output (the foam block). Hence, from this we could see that some unit operations like pumping, cooling, distillation and so on were applied. A chemical engineer has so much to do in the production of foam blocks. Hence, the production of a foam block can be said to be a chemical process.
39
REFERENCE
Harrington, Ron, Hock, Kathy;”Flexible Polyurethane Foams”, midland. The Dow chemical company: 1991
Oertel, Gunter,” Polyurethane Handbook”, New York. Macmillan Publishing Co. Inc. 1985
Ulrich, Henri, “Chemistry and Technology Of Isocynates”, New York: John Wiley & Sons Inc.1996
Experience from SIWES 400l at group enterprises Nig. Limited. Poly foam industry
40
APPENDIX CONVEYOR SPEED……………..…………………………………4.0m/s MIXER SPEED………………………………………………………..3569rpm
CHEMICAL PPH POLYOL TDI MECL 2 WATER AMINE TIN SILICONE COLOUR 2 COLOUR 1
PBW
ACTUAL ERROR(%) USED(%)
41
