Design and Synthesis of Polysiloxane Based Side Chain Liquid Crystal Polymer for Improving the Processability and Toughness of Magnesium Hydrate/Linear Low-Density Polyethylene Composites

Abstract

In this study, a polysiloxane grafted by thermotropic liquid crystal polymer (PSCTLCP) is designed and synthesized to effectively improve the processability and toughness of magnesium hydroxide (MH)/linear low-density polyethylene (LLDPE) composites. The obtained PSCTLCP is a nematic liquid crystal polymer; the liquid crystal phase exists in a temperature range of 170 to 275 • C, and its initial thermal decomposition temperature is as high as 279.6 • C, which matches the processing temperature of MH/LLDPE composites. With the increase of PSCTLCP loading, the balance melt torque of MH/LLDPE/PSCTLCP composites is gradually decreased by 42% at 5 wt % PSCTLCP loading. Moreover, the power law index of MH/LLDPE/PSCTLCP composite melt is smaller than 1, but gradually increased with PSCTLCP, the flowing activation energy of PSCTLCP-1.0 is lower than that of MH/LLDPE at the same shear rate, indicating that the sensitivity of apparent melt viscosity of the composites to shear rate and to temperature is decreased with the increase of PSCTLCP, and the processing window is broadened by the addition of PSCTLCP. Besides, the elongation at break of MH/LLDPE/PSCTLCP composites increases from 6.85% of the baseline MH/LLDPE to 17.66% at 3 wt % PSCTLCP loading. All the results indicate that PSCTLCP can significantly improve the processability and toughness of MH/LLDPE composites.Polymers 2020, 12, 911 2 of 15 low molecular weight PDMS (silicone oil) is a good lubricant for plastics [11,12]. A small amount of polysiloxane with long chain alkyl side group obviously increased the melt flow rate and reduced the processing difficulty of thermoplastic composites [13]. Moreover, it was found that the toughness of plastics composites was enhanced with the increase of PDMS loading [14]. However, PDMS is a typical liquid polymer and cannot be conveniently used in industrial production, compared with powdered processing aids.Thermotropic liquid crystal polymer (TLCP) possesses the excellent mechanical properties and lubrication for thermoplastic polymer melts [15,16]. During the melting process, the rigid TLCP macromolecules are easily oriented and arranged along the flow direction under the action of shear or tensile force, and ultimately improve the processability of thermoplastic composites [17][18][19][20].However, for TLCP, the prerequisite for improving the processability of thermoplastic composites is that the liquid crystal phase transition temperature range is consistent with the processing temperature of thermoplastics [21]. Unfortunately, at present, the melting temperature of most main chain thermotropic liquid crystal polymers is quite high and is just comparable to that of the engineering plastics with high processing temperature [22], but is not well matched with the polyolefins with lower processing temperature [23]. Therefore, it has attracted more and more attention to reduce the melting point of the thermotropic liquid crystal polymer and further to expand its application in polyolefin-based thermoplastic composites with low...

Syntheses, Characterization and Acidochromic Properties of Donor‐Acceptor‐Donor Compounds Based on 2‐Amino‐Pyrimidine

“…This temperature marks the transition from the anisotropic to isotropic phase of the liquid crystals, as indicated by the measured phase transition enthalpy of the AETP.The associated phase transition enthalpy (ΔH) is meas-ured to be 11.49 kJ/mol, which is indicative of the phase transition from anisotropy to isotropy of liquid crystals. [29] The temperature corresponding to the larger exothermic peak value is 164.7 °C, which is the melting temperature (Tm) of ATP. This compound can be used as a potential material in liquid crystals.…”

Grafting of thermotropic fluorinated mesogens on polysiloxane to improve the processability of linear low-density polyethylene

“…[6][7][8][9] In the melting process, TLCPs in the liquid crystal phase are easily oriented and arranged along the ow direction under the action of shear force or tension, therefore improving the processability of thermoplastic composites. [10][11][12][13][14] Nevertheless, the main drawback of most main chain TLCPs is the high melting temperature, and it greatly connes their use to engineering plastics which are tolerant of higher processing temperature. 15 In this regard, only few main chain TLCPs meet the requirement of low processing temperature system, such as polyolen based thermoplastic composites.…”

“…6–9 In the melting process, TLCPs in the liquid crystal phase are easily oriented and arranged along the flow direction under the action of shear force or tension, therefore improving the processability of thermoplastic composites. 10–14…”

Rheology and Processing of Polymers

“…To effectively improve the processability and toughness of magnesium hydroxide (MH)/linear low-density polyethylene (LLDPE) composites, a polysiloxane grafted with a thermotropic liquid crystal polymer (PSCTLCP) was designed and synthesized by Xiaoxiao Guan et al [14]. The effect of PSCTLCP loading on the processability and tensile properties of MH/LLDPE/PSCTLCP composites was studied.…”