Utilization of Maize Husk as Filler for Production of Polyurethane Foam.

FOAM

Foam is a composite structure made up of two or more components, which are analyzed on the basis of structure of various components, concentration, types and degree of dispersion.

It consists of a mass of gas bubbles dispersed in a solid or liquid (glassy matrix) (Jeffcat, 2006).

Foam is either a thermoplastic (Soft and bendable when heated) which is made by expanding the plastic to a sponge like structure during processing or thermosetting. This is by adding chemicals such as polyol, toluene diisocyanate, silicone oil, which decompose with the liberation of gas at a critical point in the fabrication. This expansion may also be done by dissolving a gas in the plastic under condition that will allow the gas to come of solution, later with the formation of bubbles.

The properties of foam depends on the particle size of the filler which may be reinforcing or non-reinforcing or the sizes of the cells or bubbles in the foam (Benning, 1969).

The degree of dispersion of the filler in the solid filled composite and the cell structure of the foam determines the mechanical properties. By this, foam having small uniform cells have improved mechanical properties in comparison with a diversity of the cell structure (Williams, 1995).

Types of Foam

The two major types of foam are thermoplastic foam and thermosetting foam. These classifications are based on the cure and its cross-linking. Examples of each are shown in the table below.

Table 1: Types of Thermosetting and Thermoplastic Foams.

Thermoplastic Foams Thermosetting Foams
Polystyrene

Polyethylene

Polyvinylchloride (PVC)

Polycarbonate

Polyester

Nylon

Polyurethane

Polyiisocyanurate

Phenolics

Urea formaldehyde

Epoxy

Silicon

 

Polyurethane Foams

Polyurethane foam is formed by the reaction of the polyiisocyanate with polyol and other minor ingredient such as stannous octoate e.t.c. The synthesis of polyurethane foam involves gas evolution proceeding with chain lengthening and cross-linking. The gas is usually carbon dioxide Because of the distinguished chemical and physical properties such as hardness, cell structure and raw materials, its vast application includes fibres, adhesives, coating, moulding, elastomers and then foams (Driver, 1979).

Classification of Polyurethane Foams

Foams are classified into flexible foam based on their degree of cross-linking and mechanical properties. Each class greatly determines its area of application (Randall, 2002).

 

  1. Flexible Foam: This is formed from the reaction of triol with Diphenylmethane 4,4 diisocyanate (MDI). They resilient with Toluene diisocyante (TDI). They resilient with open cell structure low degree of cross-linking, low density and tend to collapse above certain loading. They find use in rug underlay, car seat, fabric foam laminate, in cushioning and clothing etc.
  2. Rigid Foams: This is obtained when MDI reacts with Polyol of functionality greater than three. They posses higher density, poor resilience, closed cells, low heat transmission rate and high degree of cross-linking.

They are used for electrical insulation, pipe, roofing automotive spare parts and some domestic ware (Adeleke, 2001).

Basic Chemistry of Polyurethane Foam Formation

The basic chemistry of polyurethane foam formation is divided into two (Jeffs, 1993).

  1. Blowing Reaction: this is the reaction between Isocyanate and water, which

Produces carbon dioxide and biuret.

  1. R – N = O + H2O R – NH2 + CO 2

Isocyanate    Water     Amine     Carbon dioxide

  1. The amine obtained from reaction (1) will react with Isocyanate to produce substituted urea (Jeffs, 1993).
  2. R – NH2 + R –N= C = O      R-HN –C –NH –R

Amine      Isocyanate           Substituted Urea

iii.   The substituted urea are themselves active hydrogen compounds and futher reaction can take place with any remaining Isocyanate to give the biuret (Jeffs,1993).

 

CO –NH –R

R –NH –CO –NH –R + R –N =C =O       R –N –CO –NH –R

 

Substituted Urea

Polymerization Reaction: This is the reaction between Isocyanate and Polyol, which primarily reacts to produce urethane linkage that is later turned to an Allophanate during the curing stage. The formation of the urethane takes place during the expansion of the foam.

Reaction

 

O
  1. R –OH + R –N =C =O R –NH –C –O –R

Polyol      Isocyanate

 

Urethane Linkage

  1. R –NH –C –O –R + R –N =C =C R –NH –C –N –C –O –R

Urethane Linkage     Isocyanate

Allophanate

Objectives of the Project:

  • To produce foam from Maize Husk
  • To test the quality of the product and compare with the existing products in the market.
  • To check-mate fire outbreak in the foam industries.

CHAPTER TWO

LITERATURE REVIEW

Concept of Rigid Polyurethane Foam

Polyurethane foams has one of the lowest thermal conductivity rating of any insulant that allows efficient retention of heat or alternatively maintenance of a refrigerated or frozen environment (Jeffcat, 2006). They are branched or cross-linked polymer formed when the functionality of the hydroxyl or Isocyanate is increased to two or more. They are tougher and have close cell structure. Like flexible foams, they can be made in a range of densities from less than 10kg/m3 about 1,100kg/m3 almost solid polyurethane depending on the usage. The major proportion of rigid polyurethane production consists of light weight foams for thermal insulation with density from about 28 to 50kg/m3. Hence they were classified as low density polyurethane foam or high-density polyurethane foam (Bruins, 1969).

Properties of Rigid Polyurethane Foam

  • High strength of weight ratio
  • Low water absorption
  • Resistant to compression
  • Light weight
  • Low thermal conductivity
  • Low resiliency
  • Ability to form strong adhesive bond with many materials (fillers).

 

Basic Application

The low thermal conductivity and efficient insulation of rigid polyurethane foam enable it to be used in a wide variety of area such as (John, 1990);

  • For insulating household refrigerators
  • In solar technology
  • For rail road cars
  • In pipe lagging
  • For interior liners of vehicle

 

Chemical Components and Functions

Basically, there are five essential components of rigid polyurethane foam formation namely, Polyol, Surfactant, Isocyanate, Blowing agent and Catalyst. Occasionally, some others like color and fire retardant may be added to achieve some desirable characteristics (Peet, 1979).

Polyols

Polyols are compounds containing at least two hydroxyl group but three or more hydroxyl groups for rigid foams.

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Acct. Name - Uwadia Eyemeka
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