Preparation and properties of pore-filling membranes based on sulfonated copolyimides and porous polyimide matrix

The porous polyimide films were prepared by a wet phase inversion process. The influence of coagulating non-solvent on morphology, pore size and porosity of porous films was investigated. A series of pore-filling sulfonated polyimide (PFSPI) membranes, which derived from a homogenous spongy-like porous polyimide film as matrix filled with sulfonated copolyimides, were prepared and characterized. These PFSPI membranes exhibited excellent thermal stability with desulfonation temperature of 283–330 °C and good oxidative stability in Fenton's agent due to the protective effect of porous polyimide matrix on the sulfonic acid groups. The swelling of PFSPI membranes could be effectively suppressed by the porous matrix, which leads to the excellent dimensional stability and good water stability of membranes. The PFSPI membranes exhibited high proton conductivity at elevated temperature. All the PFSPI membranes displayed better permselectivity as compared with Nafion 115, which is attributed to their much lower methanol permeability.     

Synthesis and characterization of sulfonated polyimides bearing sulfonated aromatic pendant group for DMFC applications

A novel side-chain-type sulfonated aromatic diamine, 5-[1,1-bis(4-aminophenyl)-2,2,2- trifluoroethyl]-2-(4-sulfophenoxy)benzenesulfonic acid (BABSA) was synthesized and characterized. Two series of sulfonated polymides (SPI-N and SPI-B) were prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) or 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA), sulfonated diamine BABSA and various non-sulfonated aromatic diamines. The resulting sulfonated polyimide (SPI) membranes exhibited good dimensional stability with isotropic swelling of 7-22% and high thermal stability with desulfonation temperature of 283-330 °C. These membranes also displayed excellent oxidation stability and good water stability. The SPI membranes exhibited better permselectivity than Nafion 115 membrane due to their much lower methanol permeability. The ratios of proton conductivity to methanol permeability (Ф) for the SPI membranes were almost two to three times of that for Nafion 115. The SPI-N membranes exhibited excellent conducting performance with the proton conductivity higher than Nafion 115 as the temperature over 40 °C, which attributed to their good hydrophobic/hydrophilic microphase separation structure.     

The Enhanced Performance of Polyethylene Composite Separators by the Modification of Lithium Salt@SiO2 Nanoparticles

Improving the dimensional thermal stability and electrochemical performance of polyethylene (PE) membrane is critical to enhance the safety performance of lithium-ion battery. In this paper, PE membranes are modified by lithium bis(trifuoromethanesulfonyl)imide (LiTFSI) solution and then coated with nano-SiO₂/polyvinyl alcohol solution to obtain composite membranes (PE@LnSiO₂, where n represents the concentration of LiTFSI solution). The obtained PE@L4SiO₂ (LiTFSI solution concentration is 4%) composite membrane possesses a thermal shrinkage rate of only 17% at 150 °C, which is far superior to that of the PE separator. The ionic conductivity of the composite membrane is 16.9 × 10⁻⁴ S cm⁻¹ at room temperature (RT), and the battery impedance decreases to 154 Ω, which is remarkably better than that of the PE membrane (188 Ω). The battery delivers a reversible discharge capacity of 164 mAh g⁻¹ at 0.2 C under RT after 250 cycles, and the coulomb efficiency remains above 99%. The battery also has a high discharge capacity of 132 mAh g⁻¹ at 2 C, which indicates that it has excellent rate performance. Therefore, this research successfully explores a simple method to effectively improve the dimensional thermal stability of PE separator, as well as the electrochemical and safety performance of lithium battery.     

Sulfophenylated Poly (Ether Ether Ketone Ketone) Nanofiber Composite Separator with Excellent Electrochemical Performance and Dimensional Thermal Stability for Lithium-Ion Battery via Electrospinning

In this investigation, the sulfophenylated poly (ether ether ketone ketone) (SPEEKK) separators for lithium-ion batteries (LIBs) are prepared via electrospinning. The electrospun sulfophenylated poly (ether ether ketone ketone) membranes (es-SP) are then modified with lithium bis(trifuoro-methanesulfonyl)imide (LiTFSI) by immersing in the LiTFSI/ethanol solution to obtain the modified es-SP composite separators (es-SP-Li). SPEEKK displays excellent dimensional thermal stability, and thus the thermal shrinkage of es-SP-Li-20 (20% of LiTFSI in ethanol) composite separators is only 2% after 0.5 h at 200 °C. The strong polarity of sulfonic acid groups on SPEEKK and LiTFSI enhances the electrolyte wettability and uptake, and thus afford more Li source, so as to promote the conductivity of lithium ions in the composite separators, which in turn exhibit positive impacts on the rate and cycling stability performance of LIBs. The Li//LiFePO₄ cells assembled with es-SP-Li-20 separator demonstrate excellent electrochemical stability over 170 cycles at 0.2 C with a reversible discharge capacity of 153 mAh g⁻¹, and a promising rate capacity at 2 C. In short, the as-prepared es-SP-Li composite separators with excellent comprehensive property emerge as a promising application in LIBs.     

Electrospun flexible calcium zirconate fiber membrane with excellent thermal stability and alkali resistance

Ceramic fibrous membranes have promising application in gas solid filtration and in areas requiring high thermal insulation, as well as catalyst supports, owing to their high porosity and low thermal conductivity. However, achieving flexible ceramic fibrous membranes that are stable at high temperatures remains a challenge. In the present work, a CaZrO₃ fibrous membrane with excellent stability at 1200 °C and good flexibility at 1100 °C was achieved using a combination of sol-gel and electrospinning methods. The thermal decomposition process and microstructure evolution of CaZrO₃ precursor fibers at high temperatures were discussed. The single orthorhombic phase of CaZrO₃ fibers was stable up to 1400 °C. Furthermore, the CaZrO₃ fibrous membrane exhibited excellent alkaline resistance. The excellent thermal stability and flexibility of the CaZrO₃ fibrous membrane make it a promising candidate for high-temperature applications.     

Preparation and characterization of poly(vinylidene fluoride)-13X zeolite mixed matrix membranes for lithium ion batteries' separator with enhanced performance

13X zeolite was hydrothermally synthesized and poly(vinylidene fluoride) (PVDF)/13X zeolite particles mixed matrix membranes were prepared using phase inversion method as the lithium-ion battery separator. Hydrophilic and porous 13X zeolite loading impacts on the critical separator properties of morphology, wettability, electrolyte uptake, and high temperatures dimensional stability were investigated using scanning electron microscopy, contact angle, and thermal shrinkage analysis. Electrolyte uptake of the 13X zeolite particles loaded PVDF separators increased and also the incorporation facilitated the lithium ions migration (ion conductivity) due to the Lewis acidity of their structure. The 8 wt% 13X zeolite loaded separator (S2) revealed higher porosity (~+20%), electrolyte uptake (+80%), ion conductivity (+80%), and thermal shrinkage (~−47% at 165°C). C-rate capability and cycle performance of a cell battery assembled using the S2 separator considerably improved compared with those of the assembled by the neat PVDF and commercial polypropylene separators.     

Hydroxyl terminated PEEK-toughened epoxy–amino novolac phthalonitrile blends – Synthesis,cure studies and adhesive properties

Self cure promoting, amine-containing novolac–phthalonitrile (APN) resins of varying compositions were synthesized and characterized. APN possessing amine functionalities reduced the cure initiation temperature from 310 °C (typical of pure phthalonitrile systems) to 180 °C. It showed excellent thermal stability up to 420 °C and high char residue of 77–79 %. Co-reaction of APN with diglicydyl ether of bisphenol A (DGEBA) led to a decrement in their thermal stability though improved their adhesive properties. Evidences were obtained for epoxy–amine, epoxy–phthalonitrile and amine–phthalonitrile reactions. The latter reactions led to formation of oxazoline, triazine and phthalocyanine groups in the network. These were rationalized by density functional theory studies on model compounds. The extents of epoxy–amine and epoxy–phthaonitrile reactions were quantified. Introduction of hydroxyl terminated poly ether ether ketone (PEEK) reduced the brittleness of the blends and improved their lap shear strength. Toughening of epoxy–amino novolac phthalonitrile networks occurred through phase separation of PEEK segments in cured matrix.     

Inorganic ceramic fiber separator for electrochemical and safety performance improvement of lithium-ion batteries

A separator based on ceramic fibers with excellent properties, utilized for powerful laminated lithium ion batteries, was prepared by low-cost production process. Physical and chemical characteristics of the separator and the electrochemical as well as the safety performance of lithium ion batteries were extensively investigated, and compared to commercialized polyethylene (PE) and ceramic-coating PE (C-PE) separators. The results demonstrated that inorganic ceramic fiber (CF) membrane exhibited higher porosity (85%), higher electrolyte uptake (381%) and higher ionic conductivity (1.48 mS/cm). Moreover, CF separator did not display thermal shrinkage at 160 °C for 1 h, manifesting that the separator possession of high thermal stability. The lithium nickel cobalt manganese oxide LiNi_0.5Co_0.2Mn_0.3O₂/ graphite battery employing the CF membrane displayed superior rate capability, which delivered the discharge capacities of 13.206 A h (0.2 C), 12.729 A h (0.5 C), and 12.074 A h (1 C), respectively. In addition, this battery improved cycle stability, with the capacity retention of 101.4% following 100 cycles at 1 C rate. Results of safety tests presented that batteries with CF separator passed both nail penetration and extrusion tests, implying that the safety performance was remarkably improved. Additionally, CF membrane had only 20 cents in cost for 1 Ah cells, which was ten times lower than commercial PE and C-PE separators. The perfect combination of good properties and low cost made it possible for the CF separator to be a promising separator for laminated lithium-ion batteries, which are especially used in electric vehicles.     

Poly(Vinylidene fluoride-co-hexa fluoropropylene)/Poly vinyl alcohol porous membranes for the application of fuel cells

Composite polymer electrolyte membranes PVdF-HFP/PVA were prepared by phase inversion technique. The prepared membranes were soaked in DI water and 6 M sulfuric acid in order to attain the porosity and functionality. The extended porosity was determined by scanning electron microscopy (SEM). Amorphous phase was enhanced by the inclusion of acid. Amorphous state provides a free path which causes the movement of ions leading to an increase in the conductivity. The infra-red spectroscopic measurements revealed the presence of acid moieties in the composite membranes and confirmed its functionality. Thermal gravimetric analysis showed high thermal stability of the membrane. The polymer membrane prepared with extended porosity [PVdF-HFP (7 wt.%)/PVA (4.6 wt.%)] exhibited maximum protonic conductivity due to the effect of high porous nature and the entrapment of acid moieties.     

Porous ceramics based on high-thermal-stability Al2O3–ZrO2 nanofibers for thermal insulation and sound absorption applications

Al₂O₃ fibers are promising candidates for porous ceramics, but the sudden growth of grains in the fibers above 1200 °C will limit their applications for high temperature. Herein, we reported the successful fabrication of the Al₂O₃–ZrO₂ nanofibers by electrospinning and the nanofiber-based porous ceramics by a combination of gel-casting, freeze-drying and high-temperature sintering. Results show that the addition of Zr could greatly improve the thermal stability (up to 1400 °C) of the Al₂O₃-based nanofibers, owing to the inhibition of the sudden growth of the grains in the fibers at high temperature. The Al₂O₃–ZrO₂ nanofiber-based porous ceramics after sintering at 1100–1400 °C possessed a multi-level pore structure and exhibited high thermal stability, ultra-high porosity (97.79–98.04%), ultra-low density (0.075–0.091 g/cm³) and thermal conductivity (0.0474–0.0554 W/mK), and excellent sound absorption performance with the average sound absorption coefficient of 0.598–0.770. These porous ceramics are expected to be employed in the fields of high-temperature thermal insulation and sound absorption.     

Effect of film formation process on residual stress of poly(p-phenylene biphenyltetracarboximide) in thin films

Soluble poly(p-phenylene biphenyltetracarboxamine acid) (BPDA-PDA PAA) precursor, which was synthesized from biphenyltetracarboxylic dianhydride and p-phenylene diamine in N-methyl-2-pyrrolidone (NMP), was spin-cast on silicon substrates, followed by softbake at various conditions over 80–185°C. Softbaked films were converted in nitrogen atmosphere to be the polyimide films of ca. 10 μm thickness through various imidizations over 120–400°C. Residual stress, which is generated at the polymer/substrate interface by volume shrinkage, polymer chain ordering, thermal history, and differences between properties of the polymer film and the substrate, was measured in situ during softbake and subsequent imidization processes. Polymer films imidized were further characterized in the aspect of polymer chain orientation by prism coupling and X-ray diffraction. Residual stress in the polyimide film was very sensitive to all the film formation process parameters, such as softbake temperature and time, imidization temperature, imidization step, heating rate, and film thickness, but insensitive to the cooling process. Softbaked precursor films revealed 9–42 MPa at room temperature, depending on the softbake temperature and time. That is, residual stress in the precursor film was affected by the amount of residual solvent and by partial imidization possibly occurring during softbake above the onset of imidization temperature, ca. 130°C. A lower amount of residual solvent caused higher stress in the precursor film, whereas a higher degree of imidization led to lower stress. Partially imidized precursor films were converted to polyimide films revealing relatively high stresses. After imidization, polyimide films exhibited a wide range of residual stress, 4–43 MPa at room temperature, depending on the histories of softbake and imidization. Relatively high stresses were observed in the polyimide films which were prepared from softbaked films partially imidized and by rapid imidization process with a high heating rate. The residual stress in films is an in-plane characteristic so that it is sensitive to the degree of in-plane chain orientation in addition to the thermal history term. Low stress films exhibited higher degree of in-plane chain orientation. Thus, residual stress in the film would be controlled by the alignment of polyimide chains via the film formation process with varying process parameters. Conclusively, in order to minimize residual stress and to maximize in-plane chain orientation, precursor films should be softbaked for 30 min-2 h below the onset imidization temperature, ca. 130°C, and subsequently imidized over the range of 300–400°C for 1–4 h by a two-step or multi-step process with a heating rate of ? 5.0 K min⁻¹, including a step to cover the boiling point, 202°C, of NMP. In addition, the final thickness of the imidized films should be <20 μm. © 1997 Elsevier Science Ltd.     

Investigation of nanostructures and properties of sulfonated poly(arylenethioethersulfone) copolymer as proton conducting materials by small angle neutron scattering

Sulfonated poly(arylenethioethersulfone) copolymer (SPTES-50), a promising candidate material for proton exchange membrane fuel cell (PEMFC), exhibited excellent thermal stability, high proton conductivity (135 mS/cm at 85 °C, 85% relative humidity), and electrochemical property. Small angle neutron scattering (SANS) of fully hydrated SPTES-50 membranes revealed the presence of embedded spherical nanodomains containing ionic group and water within the polymer membranes. The polydispersity of the nanoscale structure limited scattering contrast between the polymer backbone and sulfonated groups, and precluded analysis of intermediate and large scattering vectors in terms of the polymer-water interface structure. Inter-cluster correlations associated with the large extent of water absorption in the fully hydrated SPTES-50 membranes were accounted by Percus-Yevick liquid-like ordering of polydispersed hard sphere model with Schulz polydispersity approximation. Approximation of their low q upturn with an exponential decay results in a decay of −3 at 25 °C accounted for inter-cluster correlations which changed to a decay of −1.1 at 55 °C and 77 °C. This indicated a change in morphology upon increase of temperature such as to fractal morphology or an interconnected cylindrical network. The scattering patterns don't exhibit any further changes within examined range of q when the temperature increased from 55 °C to 77 °C. The number density of ionic clusters remained approximately constant (∼1.1818 × 10¹⁷ cm³), which indicated that additional water adsorbed by the polymer at the elevated temperature did not result in substantial coalescence of the clusters. Transmission electron microscopy (TEM) observation of the silver exchanged SPTES-50 membranes exhibited aggregates of Ag⁺ embedded within the dry membranes which can be approximated by isolated spheres.     

Preparation of porous-structured LiFePO4/C composite by vacuum sintering for lithium-ion battery

The LiFePO₄/C (LFP/C) composite as a cathode material for lithium-ion battery was synthesized by solid-state reaction under vacuum sintering condition (20–5 Pa). The effects of vacuum sintering temperature and time on the phase composition, morphological structure, and electrochemical performance of LFP/C composite were investigated by X-ray diffraction, scanning electron microscopy, galvanostatic charge–discharge cycling test, and electrochemical impedance spectroscopy. The synthetic LFP/C composite possessed uniform particle-size distribution with porous architecture upon sintering at 650 °C for 12 h and thus exhibited the highest discharge capacity and best cycle performance. The complete decomposition of citric acid at a suitable temperature under vacuum condition resulted in the formation of porous structure. Compared with atmospheric argon sintering, vacuum sintering method led to the formation of porous architecture, the porous sample showed excellent cycle performance with less than 2% capacity loss after 80 cycles at 0.2 C, and reached the discharge specific capacity of 87.6 mAh g⁻¹ at 10 C rate, these are better than that of atmospheric argon sintering. The LFP/C composite prepared under vacuum sintering also reduced the optimum sintering temperature by nearly 100 °C compared with that prepared under atmospheric argon sintering.     

High-Tg porous polyimide films with low dielectric constant derived from spiro-(adamantane-2,9′(2′,7′-diamino)-fluorene)

Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313.     

Chemically Modified Polyvinyl Butyral Polymer Membrane as a Gel Electrolyte for Lithium Ion Battery Applications

A novel porous membrane of chemically modified polyvinyl butyral (mPVB), with improved thermal properties and chemical stability for lithium ion battery applications, is successfully synthesized by utilizing the chain extension reaction of the OH units from PVB. The porous mPVB membranes are obtained via the tape casting and phase inversion method. The corresponding gel polymer electrolyte (GPE) is achieved by immersing the as‐prepared membranes in the liquid electrolyte. The electrochemical performances of the GPE show that the mPVB membranes have the features of good uniformity, high porosity ( ≈ 90%), great thermal stability, and high mechanical strength. Moreover, the GPE exhibits good chemical stability, a wide electrochemical window, as well as high ionic conductivity ( ≈ 1.21 × 10^?3 S cm^?1). A test of a Li/GPE/LiFePO₄ battery cell shows a capacity of 147.7 mAh g^?1 and excellent cycling stability, demonstrating the great potential of the mPVB‐based GPE for lithium ion battery applications.     

Enhanced Thermal Stability and Electrochemical Performance of Polyacrylonitrile/Cellulose Acetate-Electrospun Fiber Membrane by Boehmite Nanoparticles: Application to High-Performance Lithium-Ion Batteries

In this study, polyacrylonitrile/cellulose acetate (PAN/CA) composite nanofiber membranes with different boehmite contents are prepared by electrospinning. The physical and electrochemical properties of the composite nanofiber membrane as a separator in lithium batteries are investigated. In contrast to commercial polypropylene membrane (PP), the nanocomposite fiber membrane has a 3D network structure, higher porosity, higher thermal stability, higher electrolyte absorptivity, higher ionic conductivity, and better cycling performance. The PAN/CA composite membrane with 12 wt% boehmite has the highest ionic conductivity (1.694 mS cm⁻¹); the specific discharge capacity is 160 mAh g⁻¹ at 0.2 C discharge density and the highest capacity retention rate is 99.3% after 100 cycles. The cycle rate at 2 C has a higher capacity retention rate (88.75%). These results indicate that the PAN/CA/AlOOH composite nanofiber membrane can be expected to replace the commercial polyolefin membrane and behave as a high-performance separator for lithium-ion batteries.     

Novel aromatic polyimide ionomers for proton exchange membranes: Enhancing the hydrolytic stability

In the pursuit of the hydrolytically stable sulfonated polyimide (SPI) membranes with high proton conductivity for fuel cell applications, a series of novel SPI ionomers derived from benzophenone-4,4′-bis(4-thio-1,8-naphthalic anhydride) (BPBTNA) were conveniently synthesized. The accelerated water stability tests demonstrated that the resultant SPI membranes kept highly the original mechanical properties even after 24 h in water at 140 °C. The membranes exhibited a microphase-separated structure with high morphological stability, and well-collected hydrophilic domains that could work as proton transport channels. The proton conductivity of 1c with an IEC of 1.90 meq g⁻¹ was higher than that of Nafion at 100% relative humidity (RH).     

Lightweight and thermally insulating aluminum borate nanofibrous porous ceramics

Aluminum borate porous ceramics are excellent candidates for high-temperature insulation applications. Current research on aluminum borate-based porous ceramics mainly focuses on porous ceramics made up of aluminum borate whiskers, whose low aspect ratio leads to a relatively dense porous structure; this results in porous ceramics with low porosity and relatively high thermal conductivity. In this study, we report the manufacturing of aluminum borate nanofibrous porous ceramics by an agar-based gel casting method using electrospun nanofibers with a high aspect ratio as the three-dimensional skeleton structure. We explored the effect of the alumina/boron oxide molar ratio on the microscopic morphology and crystal phase composition of the aluminum borate nanofibers and that of the sintering temperature on the micro and macro properties of porous ceramics based on the nanofibers. The results showed that aluminum borate nanofibers with an alumina/boron oxide molar ratio of 7:2 had the densest microscopic morphology, and the corresponding porous ceramics exhibited a higher porosity (91%) and lower thermal conductivity (0.11 W m^?1 K^?1) after sintering at 1200 °C than aluminum borate porous ceramics with aluminum borate whiskers as the skeleton. The successful synthesis of aluminum borate nanofibrous porous ceramics provides new insights into the development of high-temperature insulators.     

聚丙烯腈/聚酯无纺布微孔复合锂电隔膜的制备及性能

为了改善锂电隔膜的耐热性、电解液亲和性和机械性能,本文以聚丙烯腈为主要材料,采用相转化法制备了聚酯无纺布支撑的聚丙烯腈微孔复合锂电隔膜,对隔膜的理化性能（孔道结构、机械性能、电解液性能和耐热性）和电池性能（循环性能、倍率性能）进行系统研究。结果表明,复合隔膜具有均匀的微孔结构,平均孔径约为425nm,孔隙率为74%,拉伸强度为30MPa;电解液亲和性良好,吸液率为385%,接触角接近0°,锂离子电导率较市售隔膜显著提高,达到1.65mS/cm;在150℃、0.5h的热处理条件下,复合隔膜的热收缩率为0。鉴于良好的理化特性,该隔膜所装配的钴酸锂/锂金属电池表现出优异的循环容量和倍率容量保持性,如在0.2C倍率下,经历200次循环后电池的放电容量保持率为95.2%,在10C倍率下电池的放电容量为0.5C倍率下的58.3%。因此,相转化法制备的聚丙烯腈基微孔复合隔膜在锂离子电池中显示出较好的应用前景。     

Lightweight porous silica-alumina ceramics with ultra-low thermal conductivity

Thermal protection has always been an important issue in the energy, environment and aerospace fields. Porous ceramics produced by the particle-stabilized foaming method have become a competitive material for thermal protection because of their low density and low thermal conductivity. However, the study of porous ceramics for composite systems using particle-stabilized foaming method was relatively rare. Here, silica-alumina composite porous ceramics were prepared by particle-stabilized foaming method, which was achieved by tailoring the surface charges of silica and alumina through adjustment of the pH. Porous ceramics exhibited porosity as high as 97.49% and thermal conductivity (25 °C) as low as 0.063 W m^?1 K^?1. The compressive strength of porous ceramics sintered at 1500 °C with a solid content of 30 wt% could reach 0.765 MPa. Based on the light weight and excellent thermal insulation properties, the composite porous ceramic could be used as a potential thermal insulation material in the spacecraft industry.