Study Properties Of Polyxymethene-matrix Nanocomposites Prepared By Melt Blending

With the advancement of nano technology, it has been has been attracting increasing attention for theapplication of nano particles replacing micron in modification polymer by the virtue of unique properties ofnano-particles. Although nano particles exist in matrix as the dispersed phase, the interaction ofnano-particles with polymer matrix directly affects the overall modification effects. In this paper, aminogroup and methyl group functionalized nano-silica （coded as RNS and DNS） and unmodified and modifiedtitanium dioxide nano-tubes（coded as TNTs-U and TNTs-M） and unmodified and modified titaniumdioxide nano-fiber（coded as TNF-U and TNF-M） were separately used as nanofillers to preparepolyoxymethylene（POM）-matrix nanocomposites by melt blending. The mechanical properties ofas-prepared POM-matrix nanocomposites and their thermal decomposition behaviors were measured, aswell as the dispersion of different functional nano-silica and titanium dioxide nano-tubes in POM-matrixnanocomposites. Moreover, the crystallization behaviors of POM/different functional nano-silica and theflame retardation of POM/titanium dioxide nano-tubes nanocomposites and POM/titanium dioxidenano-fiber nanocomposites were studied. The results showed that the surface functional groups and themorphology of nano-fillers had significant effects on the properties of POM-matrix nanocomposite.In this dissertation, the main contents and research results are as follows:1、The TEM images of POM nanocompoites showed that DNS dispersed well in POM matrix at thecontent of1.0wt%because of the methyl on DNS surface, and at that content the aggregates of RNSdispersed in the POM matrix unevenly with reason of more active amino groups on RNS surface. Due tolarge specific surface and large number of hydroxyl groups exposed, TNTs-U were prone to agglomeratewith the condensation between hydroxyl groups in the processing and the severely agglomerate of TNTs-Udispersed in the POM matrix at the content of0.5wt%. In comparison with TNTs-U, the aggregates ofTNTs-M got improvement at the content of0.5wt%, because some hydroxyl groups of TNTs-M wereconsumed through chemical bond with coupling agent, living less hydroxyl groups on the surface ofTNTs-M than TNTs-U.2、The results of mechanical properties test of POM nanocompoaites showed that both DNS and RNS reinforced the strength of POM, but DNS and RNS could toughen POM only at low content, when thedosage of DNS at0.5wt%and RNS at0.3wt%, the toughness of POM nanocomposites was improved by15%and16%, respectively. However, the impact toughness of POM/nano-silica nanocomposites tended todecline with the nano-filler further increasing, and the decrease of toughness of POM/RNS nanocompositeswas more serious than that of POM/DNS nanocompoaites at same filler content because of the moreserious aggregation of RNS in POM matrix than DNS. The addition of TNTs-U made the decrease of themechanical properties of POM/TNTs-U nanocomposites because of severely aggregates of TNTs-U. WhileTNTs-M could brought a slight improvement in tensile strength and Young’s mouduls at low content, butdecreased toughness of POM/TNTs-M nanocomposites. The improvement of TNF-M in the mechanicalproperties of POM was higher than that of TNF-U, especially in impact toughness. When the dosage ofTNF-U was at0.3wt%and TNF-M at0.1wt%, the toughness of POM nanocomposites was improved by11%and23%, respectively.3、XRD、PLM and DSC were adopted to analyzed the crystallization of POM/nano-silica composites.The results showed that the introduction of DNS and RNS did not change the crystal form of POM matrix.Besides, both of POM/DNS nanocomposites and POM/RNS nanocomposites had higher crystallizationonset temperature and smaller grain size than neat POM, which was due to the heterogeneous nucleationeffect of DNS and RNS. While, with the existence of DNS and RNS in POM nanocomposites thecrystallization half-time t_1/2increased and the kinetic constant Ztdropped with the reason of DNS and RNSprolonging the process for POM molecular chains to move towards proper crystal nuclei. For POM/DNSnanocomposites, due to the well dispersion of DNS in POM matrix the crystallization onset temperatureand t_1/2had little change with the amount of DNS, while the aggregates of RNS appeared at high RNScontent in POM/RNS nanocomposites, the interaction would be decreased with the appearance of RNSaggregates and the crystallization onset temperature and t_1/2increased firstly and then decreased with theRNS increasing.4、The thermal stabilities of POM nanoconposites with different nanofillers were evaluated by TG. Ithad been found that the incorporating RNS increased the thermal stability of POM-RNS nanocomposites,leading to an increase of initial decomposition temperature by about27℃; but the introduction of DNS hadlittle effects on the thermal decomposition behavior of POM. The reason lied in that RNS containing surface amino group could absorb formaldehyde and formic acid generated via thermal decomposition ofPOM but that DNS with surface methyl group cannot absorb formaldehyde and formic acid. Moreover,both the incorporating TNTs-M and TNTs-U could increased the thermal stabilities of POMnanocomposites, through the absorption of formaldehyde with the large specific surface area and absorptioncapactity of TNTs, which lowered the rate of decomposition of POM. While at high content of TNTs, thedehydration condensation between hydroxyl groups would be happen when suffering shear force and heatduring the processing and water could accelerated the initial decomposition of POM at lower temperature.With account of more hydroxyl groups on the surface of TNTs-U, the dehydration condensation betweenhydroxyl groups of TNTs-U were more serious and decreased thermal stabilities of POM/TNTs-Unanocomposites more badly, and the existence of TNTs-U at1.0wt%and TNTs-M at2.0wt%decreased theinitial decomposition temperature. Because the fiber has non the ability of absorption of formaldehyde, theimprovement of thermal stability of POM was little with the addition of TNF. While at the high content ofTNF, the dehydration condensation between hydroxyl groups would be happen and the stabilities of POMwere lower.5、According to the results of study of the flame retardant property of POM with the oxygen indexapparatus, the addition of TNTs and TNF made little influence on the oxygen index of POMnanocompoaites, but it was notable that the existence of TNTs decreased the performance of melting anddropping and prompted the formation of carbon, which was due to the capability of oxygen adsorption ofTNTs with the help of large specific surface area. By compared with TNTs, the effect of TNF on carbonformation was weaker.