Preparation Of Thermally Conductive Polymer-based Composites With Anti-pathogen Functionality And Its Application In The Field Of Medical Equipment

Polymer materials are widely applied as the housing of medically electronic devices attribute to their advantages of lightweight,inexpensive,insulation,excellent processability.In recent years,the medically electronic devices of modernization had gradually developed in the direction of small,lightweight,thinner.Many electronic components are installed in a compact space.However,most medically electronic devices must keep continuously working for hours or even longer,while the plastic housing like a‘thermal insulation layer’due to its poor thermal conductivity,leading to the continuous heat accumulation in the plastic housing,this problem will cause devices malfunctioning or even permanent damage.Besides,the hospital must keep adequate cleanliness,preventing bacterial adhesion and growth on the equipment surface.Nevertheless,most plastic housings provide an ideal substrate for bacteria breeding,and these bacteria can be transferred to susceptible patients directly from the medically electronic devices or by the hands of the doctor,healthcare workers,and visitors.Besides,the 2019 coronavirus（COVID-19）outbreak has severely affected people’s health and lifestyle.Wearing surgical masks can prevent the virus from the outside to enter our respiratory tract and lungs,reducing the risk of infection.However,most people face difficulty in adapting to wear surgical masks for a long time because they will feel an uncomfortable sweltering sense.To relieve this uncomfortable feeling,people will often touch or take off the face masks;this behavior will increase the risk of infection.Additionally,improving the service life of surgical masks is another significant concern.The worldwide usage of surgical masks is more than 129 billion pieces every month;the used surgical masks will produce a considerable amount of plastic waste.Most countries adopt incineration to treat these plastic wastes,but the resulting toxic gases and high carbon emissions will seriously damage the environment.The easy growth of bacteria is one of the main causes of limiting the service life of surgical masks.Surgical masks have insufficient antibacterial activity;they are easy to become a breeding ground for bacteria and might even bring an additional infection risk for users.As a result,to ensure a clean respiratory environment,people must replace masks frequently,thus creating an enormous environmental burden.（1）Quaternary ammonium compounds（QACs）with a broad-spectrum antibacterial activity were grafted onto the surface hydroxylated hexagonal boron nitride（h-BN）nanoparticles by covalent bonding.The QACs@h-BN nanoparticles were filled into the linear low-density polyethylene（LLDPE）via the melt blending method to prepare the QACs@h-BN/LLDPE nanoplatelet composites with thermal conductivity and antibacterial activity.Morphology analyses（SEM）revealed that the introduction of organic chains onto h-BN also improved the degree of interface combination with LLDPE significantly,which promoted more efficient heat transfer.The thermal conductivity of the 25 vol%QACs@h-BN/LLDPE nanoplatelet composites could reach 1.115 W/m K;this value distinctly exceeded that of the unmodified h-BN/LLDPE nanoplatelet composites（0.926 W/m K）.The EMA results showed that the interface thermal resistance of QACs@h-BN/LLDPE nanoplatelet composites was 1.904×10^-7 m²K/W,which much lower than the unmodified h-BN/LLDPE nanocomposite(3.927×10^-7 m²K/W),confirming the introduction of QACs enhance the adherence between LLDPE and h-BN.The results of the antibacterial test indicated that the unmodified h-BN/LLDPE nanocomposite has almost no antibacterial activity against E.coli and S.aureus,but the QACs@h-BN/LLDPE nanoplatelet composites showed an antibacterial rate of 99%against both E.coli and S.aureus.Besides,the introduction of QACs chains can also improve the tensile strength of the composite.The tensile strength of the QACs@h-BN/LLDPE nanoplatelet composite can reach 13.6 MPa at a 20 vol%loading,whereas that of the h-BN/LLDPE nanoplatelet composite reaches 11.9 MPa.（2）Liquid metal（LQA）,as a new type of liquid filler,has many advantages that solid fillers can hardly possess.The contact angle of LQA on the cured epoxy resin substrate was 92.1°,while the contact angle was only 56.3°on the uncured epoxy resin liquid,displaying excellent wettability.When LQA was filled into liquid epoxy resin,it will be uniformly dispersed in the epoxy resin in the form of micron droplets:a certain gap was maintained between every LQA droplet to form an independent structure,but this independent structure is difficult to construct a continuous network,which is not conducive to heat transfer.However,after introducing the ceramic fillers of thermal conductivity（Al₂O₃、Si₃N₄and h-BN）,LQA and ceramic fillers will form an independent phase structure:ceramic fillers were gathered in the gaps between LQA microspheres.This mutually independent phase structure constructed a continuous network in the epoxy resin,which enabled the continuous diffusion of heat.When the filling content of LQA was 40 vol%,the thermal conductivity of Epoxy/LQA composites was 1.62 W/m K.While when 40 vol%LQA and 10 vol%ceramic filler were filled into epoxy resin simultaneously,the thermal conductivity of Epoxy/LQA/ceramic composites improved significantly;the thermal conductivity of the three Epoxy/LQA/ceramic composites were 2.24 W/m K（Epoxy/LQA/Al₂O₃）,2.31 W/m K（Epoxy/LQA/Si₃N₄）,and 2.46 W/m K（Epoxy/LQA/h-BN）,respectively.It is worth noting that the thermal conductivity of the three epoxy/LQA/ceramic composites also exceeded the sum of the thermal conductivities of the two-component composites.More importantly,the independent structures endowed the composites with excellent electrical safety.The electrical resistivity of the Epoxy/LQA composites was 8.53×10⁷Ωcm,while the electrical resistivities of the three Epoxy/LQA/ceramic composites were 3.11×10¹¹Ωcm（Epoxy/LQA/Al₂O₃）,2.41×10¹¹Ωcm（Epoxy/LQA/Si₃N₄）,4.45×10¹¹Ωcm（Epoxy/LQA/h-BN）,far beyond the standard resistance required for electrical insulation（>10⁹Ωcm）.In addition,owing to LQA has a great antibacterial activity,the antibacterial rates of epoxy resin/LQA/ceramic composites can reach 66.2%and 67.9%against E.coli and S.aureus,respectively.（3）The polypropylene（PP）ultrafine fiber nonwoven was prepared by the melt-blown method.Then,the antibacterial functionalized h-BN（QAC/h-BN）nanoparticles were loaded into the PP ultrafine fiber nonwoven to prepare a new type of mask with excellent antibacterial activity and comfort.The PM_2.5 removal efficiency of homemade PP ultrafine fiber nonwovens has a small improvement than that of commercial PP nonwoven.PP ultrafine fiber nonwovens were 94.2%;commercial PP nonwoven were 92.1%.When the introduction of QAC/h-BN nanoparticles the removal efficiency of QAC/h-BN/PP nanocomposite fiber membranes can reach99.1%.Moreover,the PM 2.5 removal efficiency of QAC/h-BN/PP-4 nanocomposite fibrous membranes still achieved 98.1%after five recycle usage.The thermal conductivity of homemade PP ultrafine fiber nonwovens and commercial PP nonwovens were 0.13 and 0.12 W/m K,respectively,but that of the QAC/h-BN/PP nanocomposite fibrous membranes reached 0.88 W/m K,an enhancement of 706.5%than commercial PP nonwovens.The surface temperature of commercial PP surgical masks was 29.7,30.8,and 31.8℃when the wearing time was 10,30,and 60 min.In contrast,QAC/h-BN/PP nanofiber composite masks can reach 32.9,33.4,and 33.6℃at the same tested time,exhibiting stronger heat dissipation than commercial PP surgical masks.Besides,the antibacterial rates of QAC/h-BN/PP nanocomposite fibrous membranes were 99.3%for E.coli and 96.1%for S.aureus,exhibiting excellent antibacterial activity.And,after five times of repeated use,the antibacterial rates of QAC/h-BN/PP can remain at 96.2%and 96.0%against the above two bacteria.（4）The carbon nanofibers（CNFs）were loaded into the homemade carbon fiber（CF）membranes to obtain CNFs/CF nanofiber membranes,and then the hydrophobic long chain of silane（FAS）was grafted onto the surface of nanofiber membranes to prepare the hydrophobic F-CNFs/CF nanofiber membranes.Finally,the F-CNFs/CF nanofiber membranes were employed as the core layer;the hydrophilic nonwovens and the hydrophobic nonwovens are the inner and outer layers,three layers were combined to obtain F-CNFs/CF nanofiber composite masks.The filtration efficiency of commercial PP nonwovens for PM_2.5 was 94.7%,while the filtration efficiency of the prepared CF membranes was only 74.1%.However,when CNFs were loaded on the CF membranes,the F-CNFs/CF nanofiber membranes shown a significant increase in the filtration efficiency,which can reach 98.2%at the highest.The thermal conductivities of commercial PP nonwovens were 0.12 and 0.20 W/m K in the vertical plane and parallel plane.The thermal conductivities of CF membranes were slightly higher than that of commercial PP nonwovens,which are 0.13 and 0.52 W/m K in the vertical plane and parallel plane.Whereas,when the filling content of CNFs was 0.20g,the thermal conductivities of F-CNFs/CF nanofiber membranes were 0.62 and 5.23W/m K in the vertical plane and parallel plane,an enhancement of 380 and 2523%than commercial PP nonwovens.The surface temperature of commercial PP surgical masks was 24.2,26.4,and 27.3℃when the wearing time was 5,10,and 15 min.In contrast,F-CNFs/CF can reach 29.7,30.8,and 31.8℃at the same tested time,exhibiting stronger heat dissipation than commercial PP surgical masks.The electrical conductivity of the F-CNFs/CF-4 nanofiber membranes can reach 35.01 Scm^-1,and they can be connected to a portable power bank to convert electrical energy into heat energy,so that the F-CNFs/CF-4 nanocomposite fiber masks can generate heat.When the power-on time was 1 min,the surface temperature of the masks can reach 69.2℃,which can effectively kill the SARS-Co V-2 in and on the surface of the mask.The antibacterial test results showed that when the power-on time was 30 minutes,the antibacterial rate of the F-CNFs/CF-4 nanocomposite mask can reach 97.9 and 98.6%against E.coli and S.aureus,respectively.