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EFFECTS OF SOME MINERAL FILLERS AND COMPATIBILIZER ON THE FLAME, MECHANICAL AND SORPTION PROPERTIES OF POLYPROPYLENE
ABSTRACT
The effects of some mineral fillers and compatibilizer on flammability, mechanical and sorption characteristics of polypropylene filled with Dolomite and Calcium diphosphate mineral have been investigated at filler contents of 0 – 20 weight%. The effect of maleic anhydride grafted polypropylene used as compatibilzer was also investigated in the range 1.5 -5.0 wt %. The compatibilized and uncompatibilized blends of polypropylene/ dolomite (PP/Dol), polypropylene/calciumdiphosphate (PP/Caphos) and polypropylene/dolomite/calciumdiphosphate (PP/Dol/Caphos) composites, and were prepared using an injection-moulding machine. The results show that PP/Dol composite gave significantly improved flame properties at 20wt% dolomite composition.the modeled curve equation for the ignition time is given as: f(x) = 9.44x2-34.88x+189.6 .Also, the results obtained indicated that calciumdiphosphate gave a flame retardant property to polypropylene to a less significant level compared to dolomite. The addition of a compatibilizer to the composite compositions reduced the ignition times of the PP/dol and PP/Caphos composites thus showing that the compatibilizer has a negative effect on the flame retardant properties of both Dolomite and Calciumdiphosphate.Also, the composites showed improved mechanical properties. The tensile strength at yield showed rapid increase at 0 – 10 wt% compositions and droped at amounts greater than 10wt% for the uncompatibilized compositions. The modeled equation for the uncompatibilised PP/dol is given as TS = -0.0007467x3+0.01029x2+0.09095x+5.046 A trend reversal was observed with the addition of compatibilizer. This appeared to increase the tensile strength above 30% for 1.5wt% but insignificant with increased wt% of compatibilizer. Both dol and Caphos reduced the elongation at break of the uncompatibilized PP but flexural strength and hardness were increased. The addition of compatibilizer witnessed improved hardness property above 30% and the combined use of both fillers improved hardness of above 50% at dol/caphos 20wt%, this trend was observed also for the compatibilized PP/dol/caphos composite,the modeled equation is given as f(x) = 0.00398x30.006114x2+0.8438x+7.967.The molar percentage solvent uptake (% Qt) had an increasing trend with the temperature. Solvent uptake increased with temperature in the order 70> 50> 30oC and the diffusion co-efficient had the order PP/Caphos > PP/Dol > PP/Dol/Caphos. Higher values of diffusion coefficient were observed with Xylene than in toluene at all temperatures considered and it increased with increase in temperature. Sorption co-efficient (S) of the uncompatibilzed composites were higher than the compatibilized composites.
Keywords: Polypropylene, composites, calcium diphosphate, dolomite, sorption
TABLE OF CONTENTS
Certification i
Dedication ii
Acknowledgements iii
Abstract v
Table of Contents vii
List of Tables xv
List of Figures xvii
CHAPTER ONE: INTRODUCTION 1
1.1 Background of the study 1
1.2 Statement of research problem 5
1.3 Objectives of the study 7
1.4 Justification for the study 8
1.5 Scope of the study 9
CHAPTER TWO: LITERATURE REVIEW 10
2.1 Composite materials 10
2.1.1 Classification of Composites 12
2.1.2 Polymer Matrix Composites 13
2.2 Effect of compatibilizers in composite manufacture 14
2.3 Burning process of flames 16
2.3.1 Phases of fire 17
2.3.1.1 Incipient Phase 17
2.3.1.2 Free- Burning Phase 17
2.3.1.3 Smouldering Phase 18
2.4 Flame Retardants 21
2.4.1 Classes of flame retardants 22
2.4.1.1 Halogen containing Retardants 22
2.4.1.2 Phosphorus containing based Retardants 23
2.4.1.3 Nitrogen containing based Retardants 23
2.4.1.4 Chlorine based Retardants 24
2.4.1.5 Inorganic based Retardants 24
2.4.2 Mechanism of flame retardants 24
2.4.3 Applications of flame retardants 26
2.4.3.1 Electronics and Electrical Devices 26
2.4.3.2 Building and Construction Materials 26
2.4.3.3 Furnishings 27
2.4.3.4 Transportation (Airplanes, Trains, Automobiles) 27
2.5 Actions of flame retardants 28
2.5.1 Health aspects of flame retardants 30
2.5.2 Types of fillers for flame retardance 31
2.5.2.1 Inorganic flame retardant fillers 31
2.5.2.1.1 Carbonates 32
2.5.2.1.2 Phosphorus-based flame retardants 35
2.5. 2.2 Organic flame retardant fillers 37
2.5.2.3 Nano-fillers-flame retardants 39
2.5.3 Principles of flame retardancy: 43
2.6 Polymer diffusion and sorption characteristics 44
2.6.1 Diffusion laws 45
2.7 Dolomite 52
2.7.1 History of dolomite 53
2.7.1.1 Formation 54
2.7.2 Composition of dolomite powder 54
2.7.2.1 Physical characteristics of dolomite powder 55
2.7.3 Application of dolomite powder 56
2.8 Calcium Phosphate 57
2.8.1 The applications of calcium phosphate 57
2.8.2 Studies on calcium phosphate 58
2.8.3 Types of calcium phosphates 60
2.8.3.1 Calcium diphosphate 61
2.9 Polypropylene 62
2.9.1 Applications of polypropylene 63
CHAPTER THREE: MATERIALS AND METHODS 65
3.1 Materials 66
3.2 Methods 66
3.2.1 Composites Preparation 67
3.2.2 Injection Moulding Process 68
3.3 Test Procedures 71
3.3.1 Flame Tests 71
3.3.1.1 Ignition Test 71
3.3.1.2 Flame Propagation Test 71
3.3.2 Mechanical Property Test 72
3.3.3 Determination of Sorption Characteristics 76
3.3.4 Matlab Modeling 77
CHAPTER FOUR: RESULTS AND DISCUSSION 80
4.1 Flammability tests 80
4.1.1 Ignition Time 80
4.1.2 Extent of Ignition Time (IT) with varying 85
filler compositions
4.1.3 Matlab Modeling of Ignition Time (IT) for 87 the Uncompatibilized Composites
4.1.3.1 Modelling of Polypropylene-Dolomite 89
UncompatibilizedComposite
4.1.3.2 Modelling of Polypropylene-Calcium 89 diphosphate Uncompatibilized Composite
4.1.3.3 Linear model Poly3 for PP/DOL/CAPHOS: 91
4.1.4 Modeling of Ignition Time (IT) for Composites at
constant 1.5 wt % Compatibilizer 93
4.1.4.1 Modeling of Ignition Time (IT) for Polypropylene
-Dolomite Composites at constant 1.5 93
wt % Compatibilizer
4.1.4.2 Modeling of Ignition Time (IT) for Polypropylene
- CAPHOS Composites at constant 1.5 95
wt % Compatibilizer
4.1.4.3 Modeling of Ignition Time (IT) for Polypropylene – Dol- CAPHOS Composites at constant 1.5 97
wt % Compatibilizer
4.1.5 Modeling of Ignition Time for varied Compatibiliser
and Constant Filler content 102
4.1.5.1 Modeling of Ignition Time (IT) for Polypropylene
- Dol Composites at constant Filler content 102
4.1.5.2 Modelling of PP/CAPHOS Composites at varied compatibilizer and constant Filler content 104
4.1.5.3 Modelling of PP/ DOL/CAPHOS Composites at varied compatibilizer and constant Filler content 107
4.1.5.4 Modeling of Ignition Time (IT) for Composites at varied compatibilizer ( wt % ) and constant 111
5(wt %) Fillers compared with the
uncompatibilized composites.
4.1.6 Flame Propagation Rate 119
4.1.6.1 Modeling of Flame propagation Rate (FPR) of the
Uncompatibilized Dolomite filled Polypropylene
composite 122
4.1.6.2 Modeling of Flame propagation Rate (FPR) of the Uncompatibilized DiCalcium Phosphate filled Polypropylene composite 124
4.1.6.3 Modeling of Flame propagation Rate (FPR) of the Uncompatibilized Dolomite /Dicalcium
phosphate filled Polypropylene composite 126
4.1.6.4 Modeling of Flame propagation Rate (FPR) of the Compatibilized Dolomite filled Polypropylene composite at 1.5(wt %) Compatibilization 129
4.1.6.5 Modeling of Flame propagation Rate (FPR) of the Dicalcium Phosphate-Polypropylene
Composite at 1.5(wt %) Compatibilization 131
4.1.6.6 Modeling of Flame propagation Rate (FPR) of the DOL/Dicalciumphosphate-Polypropylene
Composite at 1.5 (wt %) compatibilization 133
4.1.7 The Time Rate of Distance traveled 136
4.2 Mechanical properties of the composites 141
4.2.1 Tensile Strength at Yield 141
4.2.2 Elongation at Break 164
4.2.3 Flexural Strength 170
4.2.4 Hardness (Brinell) 183
4.2.4.1 Modeling of the Hardness Test Result (HD) for the
uncompatibilized Composites 190
4.3 The sorption studies 207
4.3.1 The molar percentage uptake (% Qt) 207
4.3.2 Transport mechanism 235
4.3.2.1 Mechanism of transport of Xylene through
compatibilized composite 236
4.3.2.2 Transport mechanism of Toulene through
compatibilized composites 238
4.3.2.3 Transport Mechanism of Xylene through
uncompatibilized composites 239
4.3.2.4 Transport mechanism of toluene through
uncompatibilized composites 240
4.3.2.5 Modelling of the calculated values of n and k for polypropylene/filler composites with a and without MAPP 249
4.3.3 The Diffusion co-efficient (D) 313
4.3.4 Sorption Coefficient (S) 317
4.3.5 Permeability Coefficient (P). 321
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS 325
5.1 Conclusion 325
5.2 Recommendations 327
5.3 Contributions to knowledge 328
References 329 Appendices 347
CHAPTER ONE INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Polymers enjoy enhanced commercial usage, due to a combination of a number of properties viz: cheapness, light weight, low density, and ability to be moulded into any shape as well as their design flexibility. Other properties that drive the wide use of polymers are electrical insulating properties, an almost unlimited colourability, transparency, thermal insulation, chemical resistance and water resistance.
It is the combination of the above properties that has contributed in no small measure in driving the growth of the polymer industry in the latter half of the 20th century to a phenomenal point and this shows no signs of abating. If the advantages of synthetic polymers over competing materials such as metals and ceramics are considered, it is reasonable to predict that polymers will take an even greater share of the total materials market in the future. This is because the applications of polymers are in all areas of modern economic life such as housing, transport, agriculture, automobile, medicine etc.
However, polymers, especially plastics, have some limitations which include: flammability, low strength, low modulus of elasticity compared to competing materials such as metals and ceramics. Also, some polymers degrade innocuously in real life use. In addition, most are non-biodegradable and because of environmental concerns, these limitations are a very big concern to the Industry. Flammability of polymers has become a big concern for obvious reasons. These limitations can be overcome by blending different polymers together to produce one with the combination of the properties of both, which the individual polymers alone do not have. Another means of improving the properties of polymers is by incorporating some additives such as antioxidants, plasticizers, UV stabilizers, flame retardants etc. Organic fillers such as wood flour, agricultural wastes as well as inorganic ones, such as talc, clay, mica, etc. are incorporated into the polymer matrix for diverse reasons which may include reinforcement, colouration, improvement of oxidation properties or flame properties, Some additives may serve a dual purpose giving rise to a composite that improves not just the overall property but could add other values such as the improvement of flame properties.
Most thermoplastics are flammable; burning easily when heated to a high enough temperature. Plastics being mostly hydrocarbons, combust through a process that begins as heat in the pre-ignition phase and progresses to fire, which breaks down their long-chain structure into volatile hydrocarbons, hydrogen, and hydroxyl-free radicals. These elements formed during decomposition are high in energy and react with oxygen, releasing heat and causing fire to spread.
Fire is significantly the cause of property damage and death in the big cities in Nigeria, United States, and the world at large. It had been reported that about 4500 deaths and 29,000 injuries resulting from over 3 million fires each year in the U.S (Jash & Wilkie, 2010). This led to the loss of billions of dollars and properties. The losses were sequel to the presence of clothes, wall coverings, and household items in the residential buildings. Hence, safety consequences call for fire resistant and safety polymer products and their resistance performances. Fire safety standards for electrical appliances, textiles, upholstery and many other materials and products help to minimize those losses. To meet the fire safety standards, products made of synthetic materials (plastics) are modified with flame retardants: chemicals that inhibit the ignition and spread of flames. Plastics containing flame retardants are found in homes and office buildings, cars and mass transit vehicles, furnishing, fibers, household appliances, and many other areas and applications. Examples of the diverse plastic products that require flame retardants include construction fabrics, banner films, ceiling insulation, roofing and siding, carpet backing, automotive fabrics, components in trains and planes, tent materials, stadium seating, mattress covers, television and computer housings, electric wiring, power cable etc. This makes it imperative that Polymer products to be used in such environments must be designed to protect life and property in case of fire accidents.
Several methods have been developed to enhance the flame resistance of polymeric consumer goods, to provide protective coatings against fire and to improve the escape time during the occurrence of fire (Wu, et al, 2006). Several anti-fire additives have been developed and employed but not many offer additional roles other than fire prevention or retardancy.
However this present study investigated the effects of Dolomite CaMg(CO3)2 and Calcium diphosphate fillers on the flammability, mechanical and sorption properties of polypropylene. This is paramount because, the absorption behavior of polymers when they come in contact with organic solvents is another concern. Polymers swell if they interact with the solvents at all, and the degree of this interaction is determined by the degree of cross linking. The degree of the swelling can be measured or related to the thermodynamic properties of the system (Labana, 1986). Considerable interest has been focused on the absorption and diffusion of organic solvent because their ability to permeate at different rate enhances the separation of component of their liquid mixture through polymeric membrane (Akporhonor et al. 2007, Hofmann, 1962; Frollini et al., 2003; Morton, 1987).
The density of chain entanglement and chain ends, cross link density, compatibility of both polymer and liquid type and amount of filler in addition to viscosity of the penetrant liquid and the functionality of the cross-links are determinants of the molecular transport of organic solvents (Patterman, 1986). Previous studies revealed that the transport of solvents through polymers is affected by polymer structure, cross linking density, mode of cross linking, presence of fillers, penetrant size and temperature (Ski & Baker, 1970). Thus, an understanding of the membrane transport properties, sorption, diffusion coefficient and penetration rate with respect to aromatic solvents like toluene and xylene is necessary in order to commercialize the use of the substrate under investigation.
1.2 STATEMENT OF RESEARCH PROBLEM
Polymers are exposed to fire via accidents e.g. carelessness, electrical sparks etc. These fire accidents can cause loss of lives and damage of properties as explained earlier in the introduction. Fire retardants are used to inhibit fire and suppress smoke but the traditional fire retardants like polychlorinated bisphenyls (PCBs), Polybrominated diphenyl ether (PBDE), Penta brominated diphenylether (penta BDE) and Octa BDE create other problems via dangerous fumes evolved at high temperatures. They are toxic and hazardous by just being exposed to them, inhaling etc even without contact with flames of fire or being combusted. Some toxicological hazard of flame retardants range from Neurotoxicity- some organophosphorus compounds are neurotoxic, carcinogenicity –tris (2,3-di-bromo-I – propyI) phosphate are already banned because they are shown to be carcinogenic, sensitization of the skin (and the respiratory organs) can occur at low concentrations and is because of the probable contact with impregnated textiles of importance.
These traditional retardants are environmentally unfriendly: Polychlorinated bisphenyls (PCBs) were found to be severely toxic to people and the environment, and the chemicals were banned in 1997. Next came Polybrominated diphenyl ether (PBDE) and was over the years found to accumulate in organic tissues and in the environment even in human breast milk (New thinking on Flame Retardants, 2008) and they are hormones disruptors, with links to thyroid and other health problems. Also, Penta brominated diphenylether (penta BDE) and Octa BDE have been banned by the European Union and withdrawn from production by the only U.S manufacturer. Another is Deca BDE, (U.S. Environmental
Protection Agency, 2010).
Substitutes (CFRS and BRFs) for the restricted flame retardants have emerged but turn out to be linked to health problems (Bryan Walsh, 2010). Many of these substitutes are persistent and bio accumulative and are found not only in environmental samples and house dust (Harrad et al, 2010) but also in people (Frederiksen et al, 2009) and wild life, even those located far from the original source (De Wit et al, 2006); Montie et al, 2010). TBBA – Tetrabromobisphenol A is found in eggs of predatory birds and in human milk and umbilical cord serum and it appears to have endocrive disrupting properties (Legler, 2008). This therefore necessitates that activities be geared towards developing less dangerous fire additives.
Moreover the natural or organic fillers when used as flame retardants in polymers increase the absorption of solvents by the polymer. Inorganic compounds could give further advantages like mechanical property advancement and reduce solvent absorption properties.
Hydrocarbons are basically fuels (Obidiegwu, 2012). When they burn, they exude harmful substances, gases (Charniwalla & Park;
2002). They have a wide variety of applications, including packaging, textiles (ropes, thermal underwears, carpets etc.), stationaries, plastic parts and reusable containers of various types, laboratory equipment, loud speakers, automotive components and banknotes. These uses notwithstanding, the flammability of propylene and other plastics is a great limitation. Flame retardants are meant to remedy this shortcoming.
Nevertheless, calcium phosphate and dolomite are non- toxic and will serve as cheap fillers for polypropylene. Also, they react with fire even at very low temperatures. Not only can dolomite be a flame retardant, it can also enhance other properties such as mechanical and sorption.
1.3 OBJECTIVES OF THE STUDY
The main objective of the study is to develop composites whose fillers are effective flame retardants which can provide enough escape time for victims of fire accident and also have an enhanced effect on the mechanical and sorption properties of polypropylene for its end-use. While the specific objectives are:
- to determining the flame retardant effectiveness of Calcium Diphosphate and Dolomite and any possible synergistic effect of both additives on the flammability of polypropylene. ii. to investigate the effect of Calcium Diphosphate and Dolomite additives on the mechanical properties of polypropylene.
iii. to determining the synergistic effect of calcium diphosphate and Dolomite additives as well as the influence of compatibilizer on the mechanical properties of polypropylene. iv. to determine the optimum amount of the compatibilizer suitable for the manufacture of Dolomite/Calcium Diphosphate/ polypropylene composite.
- to investigate the effects of Dolomite and Calcium Diphosphate additives as well as compatibilizer on the transport of toluene and xylene at varying temperatures.
1.4 JUSTIFICATION OF THE STUDY
Among the most common polymers used in the plastic industries today, is polypropylene. It has a wide range of applications, hence the idea of composites to improve and counter its limitations.
Calcium phosphate and Dolomite are minerals which are abundant in nature. Phosphorus based flame retardants are very effective as they volatilize into gas phase to form active radicals and act as scavengers of hydrogen (H+) and hydroxide (OH–) radicals. Phosphorous-base radicals are on average, five times more effective than bromine and 10 times more effective than chlorine radicals (Babushok et al. 2000).
On the other hand, Dolomite is a carbonate of magnesium and calcium and all carbonates release CO2 at high temperature but only magnesium and calcium carbonate release it below 10000C, with magnesium carbonate presenting the lowest release temperature of (5500C) (Sawada et al, 1979) this CO2 released does not surport burning thereby retarding flammability.
Common solvents which are in use today e.g. water, toluene, xylene, ethanol and aromatics generally are packaged with polymeric materials. It is therefore paramount to study the transport of these solvents into polymeric composites as they come in contact with the solvents via their various end-uses e.g. food packaging, drug delivering, home utensils, containers in the industries etc.
1.5 SCOPE OF THE STUDY
The scope of this research involved the preparation of compatibilized and uncompatibilized Polypropylene and Dolomite, Polypropylene and Calcium diphosphate also Polypropylene, Dolomite and Calcium diphosphate composites at various filler contents of 0%, 5%, 10%, 15% and 20% by 200g weight of the polypropylene. Maleic anhydride-grafted-polypropylene was used as the compatibilizer. It was incorporated into the composites in two different ways: Firstly, at a constant weight of 1.5% with varying weight of fillers. Secondly, the MAPP was incorporated at varying weight of 1.5%, 2.5% , 3.5%, 4.5% and 5% and a fixed 5% weight of the fillers.
The effects of these fillers and compatibilizer on the flammability, mechanical and sorption properties of Polypropylene were also analysed.
EFFECTS OF SOME MINERAL FILLERS AND COMPATIBILIZER ON THE FLAME, MECHANICAL AND SORPTION PROPERTIES OF POLYPROPYLENE