Preparation And Property Study Of Polystyrene/Diatomite/Chlorinated Paraffin Composite Flame Retardant Materials

Polystyrene (PS) is a thermoplastic polymer with a series ofexcellent properties such as water resistance, high lighttransmittance, chemical stability, easy processing as well as lowcost. It has been widely used in audio/video media, interiordecoration, ship building and transportation vehicle building,telecommunication devices and construction industry.However, because PS is composed of carbon and hydrogen,it has a fatal disadvantage--flammability. Its combustion processis accompanied by a large amount of toxic gases. At the sametime, dripping phenomenon can be observed obviously, whichmight lead to secondary fire scene easily. Therefore, the flameretardant modification of PS is mandatory for most applications.To depress the flammability of polystyrene, halogen-basedflame retardants are mostly used in the industry. But many halogen-based flame retardants release the carcinogensubstances”dioxin” and carbon tetrachloride in case of fire,which could affect the heath of human being and animalsseriously. Therefore, European Union issued the RoHS-Act toconstrain the use of hazardous chemicals includingpolybrominated diphenyl ethers(PBDE) and polybrominatedbiphenyls(PBB). Consequently, nontoxic environment-friendlyinorganic flame retardants have drawn more concern of theindustry and research institutions. Long-year study reveals thatinorganic flame retardants have relatively low efficiency. Toachieve the heavily combustible class, the addition ratio exceedsoften over40%. Moreover, the compatibility of inorganic flameretardants with polymers is very poor and their addition in highpercentage reduces often the mechanical properties of thepolymers significantly.How to solve the problems related to halogen-based flameretardants and inorganic flame retardants? Firstly, halogen-basedflame retardants with less impact to the environment should bechosen and the additive quantity should be minimized.Regarding inorganic flame retardants, the most important issueis the improvement of their compatibility with polymers. In this thesis, chlorinated paraffin (cp-70) and diatomite were chosen toprepare a new composite flame retardant which was thenapplied to polystyrene. On one hand, the addition of diatomite inrelatively high quantity could reduce the quantity ofhalogen-based flame retardant; on the other hand, theencapsulation of diatomite with chlorinated paraffin improvesthe compatibility of diatomite with polystyrene and therefore,reduces the negative influence on the mechanical properties ofthe composite materials.Diatomite contains mainly SiO2and the content is over80wt%. Because the thermal conductivity of SiO2is very low(0.06W/m·K), it can block heat transfer effectively andfunctions as a flame retardant in the condensed phase.Chlorinated paraffin (cp-70) belongs to halogen-based flameretardants with low environment impact and is still widely usedeven in the EU. It does not release the toxic substances”dioxin”and carbon tetrachloride in case of fire. It is highly efficient,low-cost and readily available. Cp-70decomposes at a relativelylow temperature and forms non-combustible gas HCl before thedecomposition of PS takes place. It works mainly in gas phase.In this thesis a variety of analytical methods was used to study the prepared composite flame retardants. Several typicalmeasurements for flame retardants such as UL-94, LOI,thermogravimetry as well as scanning electron microscopy werecarried out on the flame retardant PS. Dispersion test,shock/tensile strength test and scanning electron microscopy(FESEM) were applied to evaluate the mechanical properties ofthe composite materials. The lifting mechanism of flameretardancy and mechanical properties were discussed.The important results are as follows:1. The prepared flame retardants have smooth particle sizedistribution, stable form and is water resistant.2. The limiting oxygen index of CP15is27.6and UL94testresults in class V-0, heavily combustible. CP15canself-extinguish very quickly after ignition. At the same time, itssmoke production and the thermal decomposition rate are thelowest among the prepared materials.3. The dispersion of the composite flame retardant in polymer isimproved significantly compared to that of diatomite.4. The addition of diatomite or cp-70in PS separately candramatically reduce the tensile strength of PS (the tensilestrengths of PS/CP and PS/Dia are20%and66%lower than that of PS respectively), whereas the addition of diatomite or cp-70has no significant impact on shock strength of PS. On the otherhand, the tensile strength/shock strength of CP-15are2%lower/14%higher in comparison with the corresponding valuesof PS. Conclusively, the new composite flame retardant of thiswork does not have significant influence on the mechanicalproperties of composite PS materials.