Production Of High Quality Foam
Production Of High Quality Foam
2.0 THE ORIGIN OF FOAM
The initiation of foam came as a result of the strong desire developed by man with respect to his environment. As began to gather data of natural phenomicua, he conceived the knowledge of foam production. (Domingnes 1982). As a result, many forms and kinds of foams are in existence. The examples are cellular plastic forms which is the oldest. The cellular plastics are available in two types; closed all and open cell. In the closed cell each cell is completely closed while in the open cell, the cells are interconnected as in a sponge. To place an order for the Complete Project Material, pay N5,000 to Then text the name of the Project topic, email address and your names to 08060565721.
Account Name – Chudi-Oji Chukwuka
Account No – 0044157183
To place an order for the Complete Project Material, pay N5,000 to
Then text the name of the Project topic, email address and your names to 08060565721.These foams was formed by adding blowing or foaming agents to the resin and then heating to cause the additives to foam or by gaseous bye-product of the polymerisation reaction. Many times low boiling liquids such as a fluorocarbon is used as the blowing agent. The polymer may be foamed prior to fabrication or during the extrusion process.
The oldest rigid cellular plastic “cellular Ebonite” produced early 1920s was done using a similar process as that for making rubber foam i.e by adding vulcanizing agent to yield an ebonite matrix (Doyle 1967).
Styrofoam being the first synthetic plastic foam is another form of foam produced in Germany many decades. It was formed through the extrusion process while the development of commercial phonetic microballons in special type of synthetic foam started in 1954 as accorded by Moharen Buct and Gudgeon in 1968).
Other forms of foam are vinyl foams and area formaldehyde. It was manufactured in Germany before the Second World War by expanding the vinyl with chemical blowing agent that gives off toxic products on decomposition. It was used for thermal insulation and further investigations resulted in the use of non toxic blowing agents which give rise to market acceptance of vinyl foams.
The common foams are polystyrene and polyurethane, but all thermoplastics can be foamed. As a result, flexible foam, semurged, foam, and rigid foams in densities ranging, from 1.6 to 960kg/m3 can be made/produced. The major uses of flexible foams of density below 100kg/m3 are for bedding, furniture and automotive applications. The rigid foams are generally used as insulation and this may be applied by foaming in place or by using cut slab materials already foamed. Heavy duty structural foams are made by using solid skins of plastics to a rigid cellular one.
As a matter of fact, we will centre this research project on “polyurethane”, a form of foam. Discussions are based on production and characterization of the polymeric reaction.
The urethane linkage – NH-CO-O- is commonly formed when an isocyanate reacts with a hydroxyl compound.
R – NCO + HO-R1 R-NH-CO-O-R- R may be an ester, ether or urea groups associated and are usually more abundant than the urethane group.
Polyurethane foam is a cellular gell-like polymer formed as a result of co-polymenzation process between polyether resin and di-isocyanate. Its production originates from Germany in the late 40s (1940s).
The reasons why we centred our research on polyurethane foam is because of its advantage over other polymeric reactions.
– It is the most versatile of all foams
– Its components are reactive
– No exudation or decomposition can occur
– Can be manufactured to any degree of hardness
– It is the easiest to produce
– It has good solvent resistance
– Can be manufactured at low temperatures as 300f and up to 100%
– It can be mixed and poured by hand, by with component proportioning equipment or by plant manufacturing large slab and then cut or sliced into better/good tensile strength and tear strength.
– Better compression and recovery properties
– It also has more favourable processing condilior
– It resists fire.
2.1 STRUCTURE OF POLYURETHANE
All urethane polymers have one feature in common. They contain urethane linkages formed by the reaction of an isocyanate with a compound containing hydroxyl groups. To form a polymer, poly functional types must be used. The urethane polymer however, is a complex structure which may contain in addition, area groups derived from the reaction of an isocyanates with water or an amine. Allophanates and burrets also be present.
2.2 PROPERTIES OF POLYURETHANE FOAM
Flexible polyurethane foams have an open-cell structure and their densities vary 16-48kg/m3. Its major outlet is in upholstery. The chemical properties of flexible urethane foams are based on light weight and light strength to weight ratio.
1. They have a uniform cell structure
2. Have smooth texture
3. Have high resistance coupled with excellent resistance to tear, Abrasion, creep and flexural stresses.
4. It is very stiff, & resistant to solvent
5. Resistance to hydrolysis
6. Has little compression set
7. Can withstand temperatures up to 423k for long periods of time without the strength being seriously impaired.
2.3 CLASSIFICATION OF POLYURETHANE
Polyurethane foam can be classified into:
i. Flexible foams
ii. Rigid foams
iii. Semi-rigid and
iv. Integral foam
But according to Trappe G. (1968), polyurethane foams are classified into (1) flexible polyurethane and (2) Rigid polyurethane foams.
2.4 FLEXIBLE POLYURETHANE FOAM
Flexible polyurethane foams are of two types – low density and high density flexible polyurethane foams. The range of density is between 10-80kg/m3 low density flexible polyurethane foams covers over 50% of the total world foam production. It is mainly used in the making of furniture, bedding, and vehicles industries because of their high tensile properties while high density flexible polyurethane are – self skimming foam, semi rigid foams and nicro-cellular elastomers. In foam production, a code range of polyrols (polymeric hydroxyl) (compounds e.g. hydroxyl – terminated polyether, H – (-or)n – OH, or polyesters H – (-OCORCOOR-)n – OH, or a hydroxyl – bearing oil such as castor oil are very much available for the production of polyurethane foam.
2.5 RIGID POLYURETHANE FOAM
This consists of closed cells and their density is nominally about 32kg/m3. It is the second to flexible foams. It ranges from 6kg/m3 to about 10kg/m3 tending from height material to almost a plastic. The cell structure present tendsx to give rigidity to the foam resulting to its high strength to weight ratio. Its stiffness and strength increases with the square of the foam density but decreases with increase in temperature. It is also classified as high and low density foams. It is resistance to impact, low density rigid polyurethane foams has a high strength ratio to weight and extremely adhesive during mixing time and curing. Rigid foams adhere very well to a wide range of surfaces including metals, glass and wood. They are resistant to oil. They are used extensively in thermal insulation e.g. in appliances like freezers, refrigerators, portable insulated chests etc and also in building as insulation panels. They are also used in the marine flotation industry because of their high stiffness per unit weight, buoyancy factor and closed cell structure. Other uses are for chair, settee couch and bed shells and reproduction paneling and beams.
2.6 THE BASIC CHEMISTRY OF FOAM PRODUCTION
The chemistry of polyurethane started with the organic chemistry of the isocyamates as prepared by Wurts in 1848.
In 1884, Hentschel, developed the most convenient method of preparing isocyanate; that of phogenation of primary amines.
Until 1930s, no real commercial application was found. The present line of investigation of the polyurethane began in1937, for it was then that Dr. Otho Bayer decided to experiment with the products of di-isocyanates as a means of producing fibres or superior to nylon which would not be covered by the Dupont patent on nylon.
Reactions 2-5 inclusive results in the formulation of cross links causing first an increase in viscosity of the reaction mixture and eventually the formulation of gelled polymer.
Reaction/causes the mixture to foam due to the formulation of carbon dioxide. The amine formed in this reaction takes part in reaction 2 and contributes to the formulation of the polymer.
Reactions (3) and (5) increases the number of cross link in the polymer and therefore influences the final physical prosperities of the foam.
During the reaction of water and isocyanate, carbonic acid is produced and later to breakdown inters amine and carbon dioxide.
Further reaction of isocyanate with anime yields area.
In the practical polyurethane chemistry, the reaction of di-isocyanate with amine is very important, diamines are used as chain extending and curing agent during the manufacturing process of polyurethane. These activities of the reaction mixture leads to chain cross-linking but under suitable condition secondary reaction of isocyanate with the acutee hydrogen atom of the urethane and urea linkage to give Allophonates and Buriet linkage (cross linkage (cross linkage reactions).
2.7 POLYURETHANE CHEMICALS AND FUNCTIONS
The chemicals and raw materials raw materials used in polyurethane production are as follows:- polyol
(toluenbe Di-isocyanate TD1)
They are classified as follows:-
Main chemicals:- Polyol (polyether) Toluene di-isocyanate (TDI)
Activators: Amine catalyst (DMEA) stannons Octoate
Foam stabilizer: Sililon oil methylene chloride
2.8 MAIN CHEMICALS
POLYOL: The most flexible slabstock foam is made from polyester, polyol supplied under theshell trade name coradol. These are essentially propylene oxide and ethylene oxide copolymers with trifunctional initiator and are known as triols. The caradol polyol for flexible slabstock production have hydroxyl values in the range of 16-36 mg KOH/g. Polyol oil is almost colourless, and odourless, high viscosity liquid. The chemical formulations are based on the amount of polyol. It does not posses any hazard to the eye as such, safety glass can afford suitable protection during handling.
2.8.2 TOLUENE DI-ISOCYANATE (TDI)
This is the most common isycyanate for flexible slabstock foam. It is also called TDI isocyanate is a clear & almost odourless, low viscous liquid with a characteristics pungent smell. TDI is a toxic compound and it vapour is irritating to the mucus membrane.
TDI and polyrol reaction will give a rubber like mixture. There is an occurrence of foaming reaction when water is added, heat is released (exothermic rxn). The amount of TDI/water must be kept strictly according to the prescribed formulation by a chemical company.
Commercial grades of TDI and mixtures of the 2,4 and 2,6 isoners are controlled proportions. Two grades are supplied under the shell trade name caradate. Caradate 80: 80 parts of 2,4 isomer and 20 pad of 2,6 isomer are used for general purpose foams.
2.8.3 BLOWING AGENTS
The primary blowing agents which causes the foam to expand is carbon dioxide. Co2 is generated by the reaction between water and Isocymate.
A secondary blowing agent may be used in combination with water to produce soft forms at all densities. These secondary blowing agents are low body liquids, either inchlorofluoromethare also called F11 available as shell TCFM11 or dichloromethane also called methylene dichloride boiling point of 400c is used in slabstock production, its study has been subjected to toxicity methylene chloride could furnish more volumes of vapour per unit weight, has lower molecular weight higher porosity causes more of it to remain undesolved
Amine is the most commonly used catalyst in foam production e.g dimethyl ethabol amine (DMEA) and organo-tin catalyst e.g. Stannon Octoate.
The amines used as catalysts are moderately toxic on ingestion and are powerful skin and eye lintants. Prolonged or repeated contacts can cause an allergic reaction. Most of the amine have an unpleasant smell such that contact or getting them into the mouth is normally avoided but care must be taken to avoid skin contact or breathing the vapour and to prevent accidental ingestion.
A combination of DMEA and Stannon Octoate catalysts tends to promote the reaction and establish a proper balance between the simultaneous reaction mostly polymerization reaction (polyrol & isocyanate).
The desired product is a balance between gas formation and polymer formation so as to allow the foam rise, polymer, extends and cross-links at such a rate that the optimum cell structure and density are achieved. The balance is very important for production of foam without collapse as may be caused by insufficient polymer strength at the end of the gas evaluation. There is an effect on the polymer formation which vanes with industrial amine caused by the tertiary amine e.g. primerly water isocyanate catalyst. There is always an increase in amine level in order accentuate gas evolution resulting in increasing polymer formation rate sufficiently to offset the increase.
The amine can extend a synergistic action on the nectallorganic catalyst so that changing the amine level may change the effectiveness of the catalyst, influcucing the balance.
The amine/tin ratio in the catalyst system has a significant effect on the cell geometry of a polyurethane foam and it is believed to be the cause of many differences found among the mechanical properties of foam that are based on the same raw materials.
2.8.5 TIN CATALYST
These can cause dermatitis and imitator of the eye. There is also some hazard if they are ingested but they are relatively not volatile and vapour hazards are slight at normal temperatures, skin contact should be avoided and food factory hygiene maintained in the handling area.
This catalyst is an organo-tin catalyst. It is a viscous liquid, light yellow to brown, it has an unpleasant heavy smell/odour, it is harmless. Stannous Octoate is a cross linking agent and has a powerful influence on the cohesion and hardening of the foam.
2.9 FOAM STABLIZERS
Silicon oil is a surfactant, it is essential to the control of the foaming process. It has two function:-
i. To assist the mixing of the components to form a homogeneous liquid.
ii. To stabilize the bubbles in the foam during the expansion so preventing collapse before the liquid phase polymenzes.
Silicon is a light – odoured moderately viscous liquid with a characteristic smell which must be added in order to stabilize the foam after fully rise unit. It sets from the initial gelatinous ones to solid foam and also added to attained a desirable cell uniformity.
Water is however needed for the production of foam. Water is very essential in polyurethane foam manufacturing. The carbon dioxide which is used as a gas in the formation is got from the reaction between toluene di-isocyanate and water. Water also causes formation of primary amines which on further reactions with isocyanate forms urea linkages in the urethane polymer.
The reaction equation is given as below R – N = c = O = H2O RNH2 + Co2.
The mixing of the foam manufacturing ingredients is very important. As the basic chemistry required, mixing helps to create a homogenous phase.
Good mixing lowers the surface tension of the polyol. The tangential mixing creates any bubbles within the mixture and this ensures the sufficient initiating point for formulation.
2.12 CHARACTERISTICS FEATURES OF METHYLENE CHLORIDE (HAZARDOUS EFFECTS)
i. The vapour created irritates the eye.
ii. It affects the respiratory system.
iii. It causes headache and nausa.
iv. High concentrated methylene chloride cause cyanosis and unconsciousness.
v. It is poisionous when taken by mouth.
vi. Its solution with di-nitrogen pentaoxide is explosive likewise mixing it with lithium, sodium, N204 and HN03.
2.13 SOME POSSIBLE FAULTS, CAUSES AND THEIR REMEDIES
As the general trends are kept in mind, there are a lot of possible faults that liable erupt, it could be as a result of error an formulation, mechanical faults, mixing conditions either over mixing or under mixing. These faults can be rectified while the production is going on (machine is running) or when the pertinent facts is considered before deciding how to remedy/cancel the fault.
The possible faults are as follows:-
i. Mechanical Disturbances
This cause jerky paper movement, creases in the paper, causes uneven conveyor change in the conveyor channel. All of the above may lead to random splitting and the splitting however is confided to the shoulder and sides of the block.
As a result of our mixing, the cells of the reactants becomes very fine. The cell walls are so thin that the cell coalesses and runs together leading to split. This faults is recognized by areas of very fine cell structure surrounding the split. It is cured by reducing the degree of mixing either by reducing the stirrer speed or lower the machine pressure or by increasing the head pressure on a high pressure machine.
It may cells remains closed, as the foam coals and the internal gas pressure falls below atmospheric pressure, the foam shrinks.
If polymenzation occurs too late, the struts will be weak at the time and the cell walls burst bubbles that forms the cell foam have not burst and the foam still contains closed cells: resulting in poor resilience and a “dead” face. The unbroken walls in the closed cells reflect the light and can be seen on the cut face of the foam.
Blocking containing a low proportion of closed cell can be rendered often more open by crushing. It proportion of closed cell is high, its foam may shrink on cooling to give distorted blocks.
Causes Of Closed Cells And Its Effects
Excess silicon:- This over stabilizes the bubbles and prevent the walls from developing weak spot at which they normally burst.
Too high material temperature:- This increases the temperature as the polymenzation rate increases more than the rate of blow to ensure that balance formular at a lower temperature gives tight foam.
Excess tin catalyst:- Makes the polymenzation to fast compared to the blow reactions causes the cell wall to be too strong at the full rise time and are not burst open.
Little nucleating air or low stirrer:- This causes coarse cell structure. If the cells are large their walls becomes thick and less easily blown open.
Splits: This is as a result of formulation chemical and mechanical errors. When cell walls burst, the struts can break and since struts are shared by all the immediate surrounding cells, the result is a series struts breaking to form a split. In diagnosing the cause for split, the frequency of occurrence should be noted. If the split is continuous via the block, it is caused by formulation error but it is random (split) its occurrence is from mechanical fault. The extend of splitting could be increased by expanding gases forcing the spilt further apart and ever breaking more struts.
The later the polymenzation, the larger the spilt dye to late polymenzation usually occurs at the top edges (shoulders0 of a block where the foam is weakest, coldest (and therefore slowest to polymerize in the centre of the block where the exother is highest gas pressure.
Some Formulation Errors That Cause Split Are:
1. Too Little tin Catalyst: This occurs at regular intervals along the edges
of the block.
2. Too Little Silicon:- Leads to bubble instability at full rise, the
bubbles burst and run together to give spilt.
3. Too Much Amine Catalyst: Same as that of little tin catalyst. The
safe working ranges recommendable are cream time of 7-14 seconds, full rise time of 8-120 seconds. Atimes split could result from adding colours to or by changing the colour in previously satisfactory information. The colour/pigments may act as nucleating agent or a paste which affects the foam stability. In any of the cases, a change may upset the balance of the running condition and cause splits.
4. Too Low TDI Index: When formulating a soft foam or foam of density less than 20g, using 10-15 php of TCFmil blowing agent and a low index e.g. 103-104. For better processing, increase the indentation by adjusting H20/TCFmil balance.
SPLITS AND CLOSED FOAM
This is a combination caused by an incorrect balance of the Stannous Octoate and silicon oil surfactants levels. It is either the silicon oil is too low while Stannon Octoate is too low or the Stannon is too high while the silicon is too low.
Sink back is simply partial collapse immediate by after full rise. It is as a result of two low level silicon oil. The degree of sink back varies between <19% and total collapse sink back of <2% especially in low density foam is not regarded a serious problem. Most atimes low level Stannon Octoates causes sink back.
SCORCHING IN SLANTOCK FOAM
The term “scorch” is used to explain the pale yellow – brown colour found atimes at the centre of large block of polyurethane foams.
The causatic factor is thermal decomposition occurring in the hottest part of the block. Large blocks are prone to scorching particularly and most especially those made from high water/low TCFM 11 formulations.
2.14 CHARACTERISTICS OF FIBRE FOAMS
DENSITY:- This is a measure of mass to the volume of the foam.
Density = Volume
But volume = Length x Width x Height
:. Density = Mass (weight)
L x W x H
Its unit = kg/M3 or g/cm3
NB: The higher the foam density, the higher the quality
The strength of any foam (fibre) depends on density. The higher the density of foam, the higher the strength. An empirical relationship between strength and density is given by:
S = KD
Where S –
S = strength
K = constant of propositionality
D = density raised to the power index of 2.
This quoted data is as a result of standard test on compression, shear, and tensile strength.
Hardness of any foam depends on density. Hardness is the resistance of foam to indentation. Foam hardness is measured using a machine called hidentor. Foam hardness is expressed in Newton “N”.
DURABILITY AND AGEING
As the desire of any man is to go for a durable and long lasting product. Foam fibre of the desired quality has a wide range of durability value of 15 years. But labouratory test indicates that fibre foams contacted/contamination with petroleum products shows poor resistance.
Therefore fibre foams immersion in such liquids over a period of years is discouraged. Most especially at liquid pressure of higher centimeters of mercury than normal. In essence durability and ageing increases in years with proper handling.
HEIGHT AND VOLUME
In foam production, the volume of the block is a measure of the height and the corresponding lengths and width of the continuous slab stock. It is calculated as follows:
Volume = Length x Width x Height
It is the time required for the foam to increase in size i.e. to rise it is approximately 3 seconds. Time taken for the reaction to start and rises to its peak.
This is the time after rising stopped to the time when the conversion takes place and after which, the foam is cut to size is taken to the laboratory to check its density and as such, test for quality as it depends on the density of the foam.
2.15 PHYSICAL PROPERTIES OF FOAM POLYURETHANE
When compared with respect to most wear properties than conventional later or PVC foams, its prosperities are superior. The physical properties are as follows:-
i. Polyurethane foams have good solvent resistance
ii. Poor conduction of heat and electricity
iii. It has high absorptivity
iv. Good thermal insulation
v. Urethane foams have good resistance to transit and handling damage.
2.16 THERMAL PROPERTIES OF POLYURETHANE FOAMS
Most of the thermal properties are the important physical properties as well. The heat transfer is predominantly dependent of conduction that gaseous phase and as well exceptionally low figure for urethane foam is due to its presence in the cells of the methylene gas. The transfer of heat by radiation is directly dependent of the cell diameter and does not depend on cell size.
The general equation of heat conduction in fibre foams are as given below.
= f = g + s + r + c
f = Thermal conductivity
g = Thermal conductivity of the cell gas
s = Thermal conductivity of the solid phase
r = Thermal conductivity associated with radiation across the
c = Thermal conductivity due to convention within the cell.
Hints, for cell diameter below 10mm and constant s at the normal foam density, c = 0. g and s are very import variables and determines the performance of the foam as an insullant.
Theoretically the radiation component of conductivity varies directly with cell diameter, the longer the diameter of the cell, the higher the conductivity.
2.17 FOAM FIBRES APPLICATION (POLYURETHANE)
Due to insisant demand for mechanical properties of packaging material, the range of cellular polymers from rigid to flexible with semi rigid inclusive are used in the field. The most important properties are mechanical prosperities, cost ease of fabrication, moisture susceptibility, heat insulation and esthetic appeal.
The primary requirement for a cushioning foam as compressive property is particularly needed.
Proper material determination for cushioning application in packaging has been done by rather empirical methods.
The necessary information people design of the protective package includes:-
– The definition of the exact capability of the cushioning material.
– Definition of shock to which the item being packaged might be subjected.
– An estimation of type and degree of disturb balances to which the entire packaging might be subjected.
2. THERMAL INSULATION
This is the largest field of application for rigid materials and the second largest application cellular polymer. The greatest importance properly determining the applicability of rigid foams as thermal insulates are thermal conductivity, ease of application, cost, moisture, absorption and transmission, permanence and mechanical properties.
The major factor contributing to the use of low density cellular polymers as insulating materials are their low thermal conductivity. The thermal conductivity of other commercial insulating material are compared with those of rigid cellular plastics.
3. DOMESTIC REFRIGERATION
The refrigeration engineers considerably freedom of styling is provided by the very low thermal conductory of polyurethane plus the ease of applications and properties of foams. This has resulted in a very board use of polyurethane in home freezers and more limited use in home refrigerators. Low moisture sensitivity and performance are also very important. This advantage has been shown to out weight cost in many cases.
4 . BUOYANCY
Cellular polymers of closed cell nature and low density together with the moisture resistance and low cost resulted in immediate acceptance of these materials for buoyancy in boats and floating structure such as docks and buoys.
As each cell in the foam is a separate floating number materials cannot be destroyed by a single puncture due to rust, deterioration or penetration as sharp objects. The susceptibility of polystyrene foams to attack by certain petroleum products which are likely to come in contact boats led to the development of foam from copolymers of styrene and acrylonitile which are resistance to these materials.
The combination of structural strength and floatation has stimulated the design of pleasure boats using a foamed in place of polystyrene.
2.18 FACTORS THAT CAUSES DEFECT DURING PROCESS
A few of the notable defects in foam production are as follows:-
1. Under cutting:- This usually occur when there is delay in pouring.
The liquid reactant then flow under the already using foam mass.
2. Smoking:- This is caused by excessive TDI vapour coming from the surface of the foam, smoking occurs. The occurrence of smoking is due to excess TDI in the formulation.
3. Collapse:- The foam collapse is as a situation whereby foam rise and fall after sometime. It is usually caused by the level of silicone being low. Catalyst quality and level can equally cause collapse. Excess mixing five, as well as contaminates in the foam system gives rise to collapse.
4. Boiling:- This occurs when bubbles appear and burst on the surface. It is a result of the catalyst quality and level being too high level of the silicon surfactant used.
5. Voids:- It is as a result of small voids being randomly throughout the foam. It is caused by high mixing speed or increase in tin catalyst.
6. Deaf foam:- Takes place when foam posses closed cells and low residency. It is caused by too low silicon level or tin catalyst.
7. Crazy balls:- Crazy balls occurs when small bubbles are moving rapidly under the surface of the foam. It may be creased by splashing due to high mixing speed or the use of low pressure equipment splashing should generally be avoided.
8. Spilt:- Spilt is a result of many reasons. The split in foam is accounted for as notably among them are some chemical and mechanical errors. This occurs when the foam breaks on top or from beneath. Some of the formulation errors burst running together to give splits.
3.0 FOAM FORMULATIONS
Foam formation is the process by which various chemical proportions are determined for foam production.
As a result of chemistry of foaming process, being definitive and not empirical, thorough understanding of the stages of reactions determines the parameters below.
i. Proportions of required chemicals
ii. Reactions temperature
iii. Heat generation and absorption
iv. Extent of cross-linking
v. Approximate physical properties of manufactured foam e.g. Density and hardness.
The chemicals that are created in the foaming process are:
Toluene di isocyanate (TDI)
Auxiliary blowing agent
3.1 THE ROLE OF CHEMICALS IN FOAMING REACTION
Polyol – This chemical foams the backbone of the polymer chain.
TDI – It is an acidic chemical that creates the coq gas by reacting with water and the curing process. At this stage, cross-linking occurs and the degree of cross-linking determines the hardness of the foam to be produced.
Silicon Oil – This chemical is introduced to effect foam
stabilization i.e. to stabilize the foam when full rise position is reached and to keep the foam cells open.
Stannous Octoate:- It influences the degree of cross linking which
is directly related to foam cohesion and hardness. (Cunny stage)
Amine:- It is used to start up and maintain the reaction between TDI and
H2O. It is used to compensate for high or low chemical temperatures within certain limits.
Auxiliary Blow Agent:- This brings about an increased blowing effect during foaming. It produces lighter foam densities without increase in water level. It also cools the foam mixture.
3.2 DETERMINATION OF CHEMICALS CONSUMPTION RATES:-
The following procedures are taken in developing a practical foam formulation:-
i The foam density is decided.
ii Approximate required water level is predicted.
iii The amt of TDI is calculated.
iv Calculation of the amount of auxiliary blowing agent required.
v Assuming values for silicone, Stannon Octoates, amine and colourant by the use of graph.
vi Adjusting chemical proportions in case of introducing fillers and fire retardants.
The details of individual chemical ratio for formulation are as stated below.
Considering the density of foam as the basis for formulation, Density of foams
Produced in Nigeria rangers from 12-40kg/m3.
3.2 (1) WATER
The amount of water required for various densities are as follows:-
2.0 parts by weight (pbw) of water gives the density of 40kg/m3.
It is summarized in the table below:-
Parts by weight of water Density kg/m3
2.0 PBW 40 kg/m3
2.5 35 kg/m3
3.0 30 kg/m3
3.5 27 kg/m3
4.0 24 kg/m3
4.5 22 kg/m3
5.0 20 kg/m3
5.2 18 kg/m3
When water is used for blowing, maximum water level should be 4.5 p.b.w but
In the presence of Auxiliary blowing agent. The water level should be 5.2 p.b.w
3.2.2 TOLUENE DI-ISOCYANATE (TDI)
The consumption of TDI is in three different stages during the foaming process.
– Reaction between TDI and water.
– Curing of polyether.
– Hardening of the foam.
a) The amount required to react with water = (Parts of water) x 9.67.
b) The mount required to cure the polyether = (Hydroxyl Number of polyol) x 0.152.
The overall equation for calculating the total amount of TDI in formulation is as written below:-
Total Amt of TDI Index (atb)
Index (Parts H2o x 9.67) + (Hydroxyl)
100 (No. x 0.152)
The total amount of TDI is in p.b.w
:. The index and the hydroxyl number is always supplied by the manufacturers of TDI and Polyol
3.2.3 BLOWING AGENT
The blowing relationship between water and MC is
1 p.b.w water = 7p.b.w MC
This means that 7kg of Mc will have the same blowing effect as 1kg of water.
The equation is given by
Blow Index = p.b.w. H2O + p.b.w. MC
In practice, constant blow index gives constant density e.g
– 5p.b.w. water without MC
– 4.5p.b.w water with 3.5 p.b.w. MC
– 4.15 p.b.w. water with 5.95 p.b.w. MC
The amount to use in production varies with the density of the foam. It depends on silicone type, weak medium or strong. For foam of density 25kg/m3, the amount of silicone should be 0.88 p.b.w
The amount of amine required depends on the type and source as intensity of activity may vary.
The required quantity varies from 0.12 – 0.30 parts by weight.
The amount to be used depends on the intensity of the location wanted. The most popularly used amine in Nigeria id Dimethyl (DMEA) or DABCO.
3.2.6 STANNONS OCTOATE
As a result of the sensitivity of the foaming process to the amount of stannous octoate used, the tolerant limits are very narrow as a deviation of just 10% may cause a major foam deformity.
The normal amount of Stannous Octoate required are:
0.23 – 0.27 p.b.w. for densities above 25kg/m3
0.27 – 0.33 p.b.w. for densities below 25 kg/m3
Due to charges in polyol nature and temperature usually calls for the adjustment in the level of Stannous Octoate usage.
The amount of colourants depends on the desired foam colour shacks. Excessive use of colour causes chemical interference in foaming reaction.
3.2.7 FILLER AND RETARDANT
Its presence does not significantly affect any normal chemical reaction. There is a minor adjustments in the levels of activators.
3.3 SUMMARY OF THE FORMULATION
After translating the given formulations above to the actual weights of required chemicals.
Foam production could be done using several ways such as:
– Box foaming (Discontinuous foam production)
– Continuous foam production process
Whichever method one employs the desired product would be achieved but the most efficient method of foam production recommended is continuous foaming production process.
But at the cause of this project box foaming was used simply because it is a labouratory – scale cup – foaming since it as under controlled condition.
During the process/experimental process, it was performed at ambient temperature of 320c, the mixture was very viscous and as such affected pouring into the mould.
At the cause of productions, no given foam density are the same, this is as a result of variation caused by the combination of the following.
– Change in altitude level
– Differences in ambient conditions
– Variation in temperatures of various chemical streams
– Machine type
– The prevailing pressure in the mixing chambers
– Sensitivities of pumps
– Variation in mixer speeds.
As a result of very small quantity of TDI, and water to high amount of polyol used during the experiment, the mixture tends to be viscous and shows reluctancy during pouring, and the dire time of 1 minute was used.
The rising time was higher as a result of low amount of carbon dioxide gas generated during the reaction for the foaming process. High caring time was experienced as a result of very low TDI to water ratio.
Generally, the density of the samples were dependent upon the C02 gas generated during the foaming process and also on both TDI and water reaction as well as on the blowing agent, the density of the foams was observed to be decreasing linearly with increasing quantity of blowing agents used.
As a safety measure, precautions were taken with respect to equipment and chemical handlings. Protective material such as goggles, gas masks, hand gloves etc were put on during the foaming process.
Note that in other to maintain safe measures, Mc (methylene chloride) were used during the formulation of foams lower than density 20kg/m.
In other to produce a softer and more resilient foam, the density of the foam is kept constant by replacing water by Mc (methylene chloride). This principle or technique is applied in the manufacture of high-density soft foams.
The purity and quality of chemicals (raw materials were tested before the production). The temperate conditioning of chemicals were also considered though the foaming process is essentially exothermic (i.e. generates heat). A temperature range of 220c – 240c were used during the production, weighing and metering of ingredients were done making sure that no two or more chemicals from different sources were mixed not muding whether their hydroxyl number are the same as in the case of polyol.
Polyurethane foam can be produced by polymenzation reaction. It is produced as a result of the reaction between polyether resin and toluene di-isocyanate (i.e. polyol and TDI) in the presence of some catalysts such as Stannous Octoate and dimethylene chloride including water a blowing agents.
The quality of the polymer material formed depends greatly on the quality or proposition of the raw materials used (formulation). The prosperities and the characteristic features of the fibre material produced are also affected by the quality. These prosperities are density, apparent porosity, resilience, flammability hardness.
As the project topic says, high density foams ranging from 18-40kg/m3 were produced by varying the ratio of TDI, water and blowing agents to the quantity of polyol.
Based on the researchers made and the experiment performed (laborratory foam production). Continuous foaming process is best recommended to ensure safety and good health of the workers and the citizens as a result of toxicity. Poisonous nature of the chemicals used in the production e.g. TDI, polyol etc.
The use of protective wears such as eye goggles, lab coats/overalls, safety boots, gloves, nose mask etc is recommended.
Stannous Octoate is adviced to be dispensed separately into polyol and there should be a difference into polyol and there should be a difference of 96 hours of more between manufacturing time and testing period and a higher pressure metering of about 200hrs is recommended.
It is expected that at the end of this project, that a small scale foam industries by established to produce high quality/density foams that could scroll many purposes as in uphostry, etc and could be used or applied in scoreal fields of engineering and technology and also satisfy human wants as well create employment opportunities for many Nigeria.
Industrialists are advised to adhere strictly to the formulation and climatic conditions specified by the suppliers of chemicals in orders to actualize the desired end product and promote safety of the Nigerian citizens.
Production Of High Quality Foam
To place an order for the Complete Project Material, pay N5,000 to
Account Name – Chudi-Oji Chukwuka
Account No – 0044157183
Then text the name of the Project topic, email address and your names to 08060565721.