Aluminum Trihydroxide Research Articles

It’s not waste, it’s a resource: Utilizing industrial waste fibers/mineral fillers to attain flame retardant biocomposites

Integrating natural fibers derived from local industrial waste streams into thermoplastic starch (TPS) proves to be a promising approach towards sustainable flame retardant biocomposites. Initially, three types of waste fibers from the agave, coconut, and leather industries were evaluated for their flame retardant properties in combination with aluminum trihydroxide (ATH), an environmental friendly flame retardant. Leather fiber (BLF) exhibited the best flame retardant performance and were further investigated along with ATH and varying amounts of bentonite nanoclay to enhance the residual protective layer. The combination of multiple components shows improvement in performance while reducing the total load of filler. The images of the fire residues revealed that a more enclosed surface correlates with a reduction in the peak of heat release rate. Whereas higher amounts of bentonite does not deliver further inprovements, only 1 phr nanoclay in the novel multicomponent system of TPS, ATH, BLF, and bentonite synergistically improved the UL-94 rating from HB to V1. The proposed system brings together the different approaches using a renewable biopolymer, natural waste fibres, and envirnmentally friendly flame retardancy and thus, is striking for its combination of outstanding sustainablity, instant feasability, and sufficient fire performance.

The nano-clay effect on the improvement of the thermal, flammability, and mechanical behavior of epoxy/glass fiber/ATH hybrid composites

More than 50% of the flame retardants used in the polymer and plastic industries are metal hydroxides. Among them, aluminum trihydroxide (ATH) is the most widely used due to its low toxicity and corrosiveness and its cost-effectiveness. The use of high-volume ATH in polymers reduces the mechanical properties. In this work, clay nanoparticles were added into epoxy/glass fiber/ATH hybrid composites to improve the mechanical and thermal properties of the composites. The effect of nano-clay content (1, 3, and 5 phr) on mechanical properties such as tensile and flexural strength and modulus, and thermal properties was investigated. Thermal properties were evaluated by Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). The result of mechanical tests showed that adding 3 phr of clay nanoparticles increases tensile and flexural strength by 10% and 9.2%, respectively. The flammability of the composites was measured in horizontal mode. The flammability results revealed that introducing 3 phr of nano-clay improves the flammability of the composites by 41%.

Degradation effects in FRNC jackets of optical fiber cables

AbstractIn large scale manufacturing, polymeric materials for cable jackets are subjected to high temperature and shear, what can induce degradation processes. In result, changes in structure of polymer materials can occur what is critical for their applications. Permanent market pressure on increase of productivity and product reliability as well as rigorous administrative regulations in telecommunication industry are the driving forces for development and introduction of new advanced Flame Retardant Non-corrosive jacketing materials. Despite many studies, their behavior is still neither well characterized nor understood in large-scale production. The object of studies was characterization of a relationship between processing conditions and effects of degradation of FRNC cable materials. The main goal was to find the processing factors limiting the production speed. Materials taken into consideration were two commercially available thermoplastic FRNC compounds dedicated to fiber optic cables, based on linear low-density polyethylene/ethylene–vinyl acetate composites with high loading of aluminum trihydroxide and magnesium dihydroxide fillers. Thermal degradation of cable materials was studied with use of thermogravimetry and rheometry. The series of jacket samples under different processing conditions were produced. Material processing behavior was characterized, and tensile and heat aging performance of cable jacket were tested. The results showed that the primary limiting factors for line speed increase were the melt pressure and jacket tensile performance, but neither the shrinkage nor extruder motor load. The result and general approach to the FRNC investigation can be successfully used in cable industry or in other industries involving the extrusion of FRNC materials.

Improving the Flame Retardancy of Aluminum Trihydroxide in Thermoplastic Starch Biocomposites Using Waste Fibers and Silicon-Based Synergists

Improving the Flame Retardancy of Aluminum Trihydroxide in Thermoplastic Starch Biocomposites Using Waste Fibers and Silicon-Based Synergists

Effects of Recycled Polyethylene on Natural Rubber Composite Blends Filled with Aluminum Trihydroxide and Polyurethane Waste: Mechanical and Dynamic Mechanical Properties, Flammability.

This research studies natural rubber (NR) composite blends prepared with recycled polyethylene (PE), polyurethane waste (PU), silica (SiO2), and aluminum trihydroxide (ATH) under the proper mixing conditions using an internal mixer and a two-roll mill. The mechanical, impact, dynamic mechanical, and thermal properties, together with flammability, were investigated. NR/PU composites filled with a specific SiO2/ATH concentration resulted in excellent flame-retardant properties without using PE. Adding PE causes poor flammability, while using PU and SiO2 prevents flame extensibility of the composites. In addition, SiO2 and ATH synergistically improved both mechanical and dynamical mechanical properties. This is attributed to the reinforcement of SiO2 particles inside the matrix, whereas the ATH releases water as a flame retardant. The V-0 composites tested with UL-94 showed acceptable heat resistance, strength, and durability, making them suitable for interior and exterior applications in buildings without the lightweight requirement.

Two‐step preparation of phosphorus‐containing organoclay and its effect on fire‐resistant and mechanical properties of the flame‐retardant polyethylene composite

AbstractIn this study, a nanohybrid based on montmorillonite (oMMT2) was prepared through a two‐step method using Arquad MCB‐80 and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as intercalation agents. The nanohybrid exhibited a basal spacing of 31.5 Å, which contained approximately 12.3% of Arquad MCB‐80 and 31.6% of DOPO. Various amount of oMMT2 nanohybrid was incorporated into a flame‐retardant polyethylene system containing aluminum trihydroxide and red phosphorus with a constant total additive content of 20 wt%. The dispersibility of oMMT2 in the composite matrix was evaluated by energy dispersive x‐ray mapping and x‐ray diffraction analyses. At a content of 3 wt% in the nanocomposite, oMMT2 showed a highly exfoliated state, while at a 5% content, a partially exfoliated and intercalated state was observed. A synergistic flame‐retardant effect between the nanohybrid and the mixture of aluminum trihydroxide and red phosphorus was found. The nanocomposite loading 3 wt% oMMT2 demonstrated the best flame retardancy, achieving a V‐0 rating of the vertical burning test with a limiting oxygen index of 27.6%. Moreover, the addition of the low oMMT2 contents (≤3 wt%) improved the mechanical properties of the flame‐retardant composite.

Lightweight Biobased Polyurethane Composites Derived from Liquefied Polyol Reinforced by Biomass Sources with High Mechanical Property and Enhanced Fire-Resistance Performance.

Lightweight biobased insulation polyurethane (BPU) composite foams with high fire-resistance efficiency are interested in building effective energy and low environmental impact today. This study focuses on manufacturing lightweight BPU from liquefied bamboo polyols and biomass resources, including rice husk and wood flour. Then, they are combined with three flame retardant (FR) additives, such as aluminum diethyl phosphinate, aluminum trihydroxide, and diammonium phosphate, to improve their fire resistance performance. The physicochemical properties, microstructure, thermal stability, mechanical properties, and flame-retardant properties of the BPU composites are characterized to optimize their compromise properties. The results showed that composites with optimized FRs achieved UL94 V-0 and those with nonoptimized FRs reached UL94 HB. The limiting oxygen index exhibited that the fire resistance of BPU composites could increase up to 21-37% within FR additives. In addition, the thermal stability of BPU composites was significantly improved in a temperature range of 300-700 °C and the compressive strength of the BPU composites was also enhanced with the presence of FRs. The scanning electron microscopy observation showed an influence of FRs on the morphology and cell size of the BPU composites. The bio-PU-derived samples in this study showed significantly low thermal conductivity values, demonstrating their remarkable thermal insulation effectiveness.

Influence of airborne particle abrasion on dentin bonding effectiveness of a 2-step universal adhesive

ObjectiveTo determine the effect of airborne particle abrasion (APA) on micro-tensile bond strength (µTBS) to dentin using different air-abrasion/polishing powders. MethodsThe bonding effectiveness of G2 Bond Universal (G2B), used in etch-and-rinse (E&R) and self-etch mode (SE), was tested on bur-cut dentin and dentin air abraded/polished using six different powders (aluminum oxide 29 µm (AO29) and 53 µm (AO53), aluminum trihydroxide (AT), sodium bicarbonate (SB), sodium bicarbonate soft (SBsoft) and bioactive glass (BG); Velopex). Adhesive-composite resin specimens were immersed in distilled water at 37 °C for one week and cut into microspecimens. Half of the specimens were subjected to 50,000 thermocycles (aged). Immediate and aged μTBS to dentin were measured. Statistical analysis was performed using linear mixed-effects (LME) modeling (p < 0.05). ResultsComparing the aged bond strengths to air-abraded/polished dentin with bur-cut dentin, pretreatment with SB and SBsoft in combination with G2B used in E&R mode, and BG air polishing in combination with both application modes (E&R, SE), resulted in a significantly higher bond strength. Dentin bond strength was only significantly lower when air abraded with AO29 and using G2B in SE mode. Aging did not significantly influence bond strength for both application modes (E&R, SE), except for AO29 and AT-treated dentin, where bond strengths decrea sed significantly using G2B in SE mode. In general, G2B reached significantly higher bond strengths on air-abraded/polished dentin in E&R mode than in SE mode. ConclusionAir-abrasion/polishing did not impair dentin bond strength using G2B, except when dentin was air abraded with AO29 and using G2B in SE mode. Air polishing positively influenced the bond strength to dentin in specific groups. Clinical significanceAPA is safe concerning bonding to dentin. The E&R application mode is preferred using G2B as adhesive on air-abraded/polished dentin. Air polishing with BG positively influenced dentin bond strength for both application methods.

Effect of zinc(II) and caustic content on the decomposition of sodium aluminate solutions and relevance to the Bayer process

The impact of zinc (Zn) on the seed decomposition process of sodium aluminate solution at different caustic concentrations was investigated. The results showed that as the concentration of Zn(II) in sodium aluminate solution increased from 0 to 1000 mg/L, the decomposition efficiency of the solution and average grain size of the resulting aluminum tri-hydroxide (ATH) changed little at a caustic concentration of 141 g/L. At caustic concentrations of 160 g/L and 177 g/L, the decomposition efficiency increased from 35.8% and 21.6% to 40.6% and 24.9%, respectively, while average grain size of the ATH crystal seeds increased from 14.2 and 9.25 μm to 17.9 and 15.9 μm, respectively. The XRD, FT-IR, and SEM analyses showed that zinc can enter the ATH seeds and interact with the α-ATH crystal planes. It may also form interactions with the AlO octahedral growth structure, thus promoting solution decomposition and influencing crystal growth. The research results will provide valuable references for improving the quality of alumina products.

Flame Retardant Additives in Polylactic Acid (PLA) Photopolymer Resin for 3D Printing Digital Light Processing (DLP)

Digital light processing (DLP) technology has been developed based on stereolithography (SLA) 3D-printing principle. The biodegradable and low-cost polylactic-acid (PLA) has so far been used as polymeric material for photopolymer resin in SLA and DLP. To achieve functional SLA-processed product, the properties of such PLA has been improved, with the aim to make it flame retardant, less viscous, and having light transmittance characteristics. In this study, the liquid raw PLA photopolymer was changed by adding different contents of Ammonium Phosphate (APP), melamine cyanurate (MCA), Aluminum Tri-hydroxide (Al2O3) and Nano-silicon dioxide (SiO2) additives. The solid PLA nanocomposite specimens were printed by using DLP device according to the standard geometry for burning test UL-94 to evaluate its flame-retardant property. In addition, the printing product and residue after burning test was analyzed for their morphological characteristic by using SEM. The results showed that the low weight fraction of MCA showed excellent performance. PLA/MCA successfully kept green body form until the sintering temperature of stainless steel was achieved. It can become a reference for application DLP 3D printing products in the casting and sintering process.

Synergistic flame retardancy and electrical conductivity in di-glycidyl ether of bisphenol-A epoxy composites with polyaniline and aluminum Tri-hydroxide

This study focuses on developing and characterizing multifunctional composites based on the diglycidyl ether of bisphenol-A (DGEBA) epoxy matrix. The aim is to enhance fire resistance and electrical conductivity properties for applications in various fields. To achieve this, aluminum tri-hydroxide (ATH) was incorporated as a flame retardant (FR) agent, while polyaniline (PANI) was added to impart electrical conductivity. The composites were categorized into three groups: the first containing flame retardant (FR), the second containing PANI for conductivity, and the third containing both PANI and FR for combined effects. E 60-FP emerged as the optimal multifunctional composite, exhibiting superior mechanical properties among the tested formulations. Thermogravimetric analysis (TGA) results provided valuable insights into the thermal stability of E 60-FP, revealing that it retained 42% of its initial mass at a temperature of 600 °C. Additionally, the composite achieved a V-0 rating in the UL 94 test, confirming its excellent fire resistance. Notably, E 60-FP displayed impressive mechanical strength, with a tensile strength of 7.2 MPa and a tensile modulus of 1117.6 MPa. Its flexural strength and modulus were measured at 31.2 MPa and 2800.2 MPa, respectively. Furthermore, the composite E 60-FP exhibited remarkable electrical conductivity, measuring 6.1 × 10–6 S cm−1. These findings highlight the potential of DGEBA epoxy composites containing PANI and ATH as promising materials for applications requiring fire resistance and electrical conductivity properties.

Air-Polishing Powders’ Effect on the Color of CAD/CAM Restorative Materials

Air-polishing powders are used to remove stains from the enamel and various restorative materials, but their effect on the discoloration of CAD/CAM blocks remains scarce. Therefore, this study investigated the effect of various air-polishing powders on the color changes in different CAD/CAM blocks to predict the esthetic outcomes. Specimens were prepared from CAD/CAM blocks (Vita Mark II, Paradigm MZ100, Lava Ultimate, Cerasmart, Vita Enamic) and divided into five groups (n = 10) according to the air-polishing powder: sodium bicarbonate; aluminum trihydroxide; calcium carbonate; glycine; and erythritol. Color parameters were measured with a spectrophotometer before and after air-polishing. The color difference was calculated with the ΔE00 formula. Data were statistically evaluated with one-way ANOVA, Tukey, and two-way ANOVA tests (α = 0.05). The CAD/CAM block type and the air-polishing powder type significantly influenced the ΔE00 value, whereas their interactions did not affect it significantly. Calcium carbonate and aluminum trihydroxide significantly increased the ΔE00 values of Lava Ultimate and Cerasmart. Although none of the groups exceeded the acceptability threshold (ΔE00 = 1.8), most exceeded the perceptibility threshold (ΔE00 = 0.8). Consequently, dentists should avoid air-polishing or should repolish with care, depending on restorative material knowledge, to maintain color stability when uncertain about the material encountered clinically.

Design of Experiments-Based Fire Performance Optimization of Epoxy and Carbon-Fiber-Reinforced Epoxy Polymer Composites.

The fire performance of epoxy and carbon-fiber-reinforced polymer (CFRP) composites with and without fire retardants (FR) (i.e., ammonium polyphosphate (APP), aluminum trihydroxide (ATH), melamine (MEL), expandable graphite (EG)) was investigated. A design of experiment (DoE) approach was applied to study the single- and multifactorial effects of FR. The fire performance of epoxy and CFRP was evaluated by limiting the oxygen index (LOI) and heat release, which were obtained by limiting the oxygen index test and cone calorimetry. It was found that mixtures of 70 wt.-% epoxy, 24.6 wt.-% of APP, and 5.4 wt.-% MEL resulted in the highest LOI level of 45 within tested groups for epoxy resin and also for CFRP specimens (LOI level of 39). This mixture also resulted in the lowest average heat release rate (HRR180s) of 104 kW·m-2 and a spec. total heat release (THR600s) of 1.14 MJ·m-2·g-1, indicating the importance of balancing spumific and charring agents in intumescent systems and synergy thereof.

Photogrammetry for making real-time measurements of the deformation of fire retarded material subjected to an external heat flux

This work exploits photogrammetry techniques to make real-time measurements on a deforming material subjected to an external heat flux. Using a novel bench design and 3D reconstruction associated to image analysis, the volume of the sample can be accurately calculated. It is applied to a fire retarded polymer (ethylene-vinyl acetate copolymer containing 65 wt% of aluminum trihydroxide as fire retardant). The material shrinks and swells upon heating (heat flux of 35 kW/m2). The volume can be followed as a function of time and it provides quantitative data about the deformation of the material.

Unsaturated Polyester Resin/Aluminum Tri-hydroxide Added with Short Glass Fiber for Battery Box

A battery box made of polymer material must consider mechanical strengthand flame retardancy. One solution to increase the flame retardancy of polymers is toadd a flame retardant filler. However, sometimes adding a flame retardant filler cancause degradation of mechanical strength compared to neat polymers. The combinationof more than one type of filler or hybrid fillers can produce the optimal combination offlame retardancy and mechanical strength. An experimental study was carried out tocharacterize several composite polymer samples of unsaturated polyester (UP) resincombined with fillers of aluminum tri-hydroxide (ATH) to increase flame retardancyand short glass fiber (G) to improve mechanical strength. The DSC results show thatthe maximum endothermic of all samples occurred at a temperature of around 70 ºC.The TGA results prove that ATH and G can maintain the thermal stability of UP so thatthe composite samples were degraded at higher temperatures by reducing the rate ofweight degradation due to a temperature of around 0.1%/ºC. The burning test alsoshows that samples with ATH and G have a lower burning rate value than neat UP. Formechanical characterization, the tensile strength of the samples with ATH and G waslower than that of neat UP. However, UP/ATH/G2 showed an optimal compositioncompared to other filler compositions with a tensile strength of 41.5 MPa. This samplealso produces an optimal bending strength of 68.9 MPa and even higher than neat UP.These results were confirmed by SEM observations, in which filler G was exfoliated inthe UP. The broken G particles on the fracture surface observation prove the goodinterlock bonding between UP and G, which contributes to increasing the mechanicalstrength of the UP composite.

Modelling of the swelling behaviour of a fire retarded material under a cone calorimeter

Modelling the swelling behaviour of intumescent materials is an important and challenging issue because this phenomenon influences their pyrolysis process. It must be therefore considered to improve the predictability of pyrolysis models. The objective of this work was to implement a swelling model in the pyrolysis code Gpyro in order to predict the behaviour of a sample of ethylene vinyl acetate containing aluminium trihydroxide (EVA/ATH) polymer studied by cone calorimetry. This polymer is used for making the external sheath of electrical cables. Unlike existing works in the literature, the model implemented here, and adapted to EVA/ATH, does not require information on the densities of the initial and final materials, which makes it more predictive. To characterize the swelling, experiments were carried out to measure the evolution of the sample thickness as a function of time. The mass loss and the back surface temperature of the sample were also measured. This was done under different operating conditions. These measurements are compared with the swelling predicted by the model and the results were found to be in good agreement. The model can be extended easily to other materials.

Cooperative Effect of Chemical and Physical Processes for Flame Retardant Additives in Recycled ABS.

In the present work, the effectiveness of four non-halogenated flame retardants (FR) (aluminium trihydroxide (ATH), magnesium hydroxide (MDH), Sepiolite (SEP) and a mix of metallic oxides and hydroxides (PAVAL)) in blends with recycled acrylonitrile-butadiene-styrene (rABS) was studied in order to develop a more environmentally friendly flame-retardant composite alternative. The mechanical and thermo-mechanical properties of the obtained composites as well as their flame-retardant mechanism were evaluated by UL-94 and cone calorimetric tests. As expected, these particles modified the mechanical performance of the rABS, increasing its stiffness at the expense of reducing its toughness and impact behavior. Regarding the fire behavior, the experimentation showed that there is an important synergy between the chemical mechanism provided by MDH (decomposition into oxides and water) and the physical mechanism provided by SEP (oxygen barrier), which means that mixed composites (rABS/MDH/SEP) can be obtained with a flame behavior superior to that of the composites studied with only one type of FR. In order to find a balance between mechanical properties, composites with different amounts of SEP and MDH were evaluated. The results showed that composites with the composition rABS/MDH/SEP: 70/15/15 wt.% increase the time to ignition (TTI) by 75% and the resulting mass after ignition by more than 600%. Furthermore, they decrease the heat release rate (HRR) by 62.9%, the total smoke production (TSP) by 19.04% and the total heat release rate (THHR) by 13.77% compared to unadditivated rABS; without compromising the mechanical behavior of the original material. These results are promising and potentially represent a greener alternative for the manufacture of flame-retardant composites.

Shelter Forest Inspired Superhydrophobic Flame‐Retardant Composite with Root‐Soil Interlocked Micro/Nanostructure Enhanced Mechanical, Physical, and Chemical Durability

AbstractThe heat accumulation caused by the high power consumption of continuously upgrading electronic devices puts forward more requirements for the adaptability and durability of the flame retardant materials. Herein, inspired by the soil reinforcement effect of the shelter forest roots nearby the river and shoal, a superhydrophobic flame‐retardant ethylene‐vinyl acetate (EVA)/aluminum trihydroxide (ATH) composite with root‐soil interlocked micro/nanostructure (MEA/PGCC) is prepared by combining the micro‐extrusion compression molding and spray coating. The homogeneously dispersed ATH and the EVA with sufficient mechanical strength provide durability for the long‐term work of the MEA/PGCC composite. The root‐soil interlocked micro/nanostructure provides robust superhydrophobicity with a water contact angle of 156 ± 1.0° and a rolling angle of 4 ± 1.0° for the MEA/PGCC composite which is beneficial to improve acid and alkali tolerance, thermic resistance, and de‐icing performance. The synergism of interface and surface function prominently improves the flame retardancy of the MEA/PGCC composite, which presents a limit oxygen index of 42%, and remarkable reduction in peak heat release rate of 64%, total heat release of 23%, and peak smoke production rate of 47%. The proposed method is a promising candidate for the mass production and practical application of the superhydrophobic flame retardant composite.

Microencapsulation based fire retardant eco-friendly jute composite

Natural fiber reinforced composites (NFCs) are a promising replacement for conventional wood materials in furniture and households. However, the flammability of natural fibers limits their practical application. The composite matrix structure can be modified to enhance flame resistance. In this study, eco-friendly and cost-effective fire-retardants (FRs), micro-integrated Triphenyl Phosphate (m-TPP), and Aluminum Trihydroxide (ATH) were added physically in different concentrations to the epoxy resins (EPs). Underwriter Laboratories 94 (UL-94) flammability test revealed that the fire resistance of FR epoxy, EP88%m-TPP9%ATH3%, increased by increasing the TPP quantity with the highest V-0 rating. The thermo-gravimetric analysis (TGA) indicated a better internal structure of EP100%. However, no char residue was observed for EP100%. The highest char residue was found for EP88%m-TPP9%ATH3%, which confirmed its highest FR resistance. However, EP88%m-TPP9%ATH3% showed poor tensile, flexural, and compressional strengths. The m-TPP was a better FR than ATH. However, the mechanical stability of FR samples containing ATH is better than those containing m-TPP. Also, the addition of FRs reduced the tensile and flexural strengths; however, the compressional strength and modulus were significantly improved, which implied a potential use in the furniture industry.

Improvement of Fire Resistance and Mechanical Properties of Glass Fiber Reinforced Plastic (GFRP) Composite Prepared from Combination of Active Nano Filler of Modified Pumice and Commercial Active Fillers

Glass fiber reinforced plastic (GFRP) composites have great potential to replace metal components in vehicles by maintaining their mechanical properties and improving fire resistance. Ease of form, anti-corrosion, lightweight, fast production cycle, durability and high strength-to-weight ratio are the advantages of GFRP compared to conventional materials. The transition to the use of plastic materials can be performed by increasing their mechanical, thermal and fire resistance properties. This research aims to improve the fire resistance of GFRP composite and maintain its strength by a combination of pumice-based active nano filler and commercial active filler. The nano active filler of pumice particle (nAFPP) was obtained by the sol-gel method. Aluminum trihydroxide (ATH), sodium silicate (SS) and boric acid (BA) were commercial active fillers that were used in this study. The GFRP composite was prepared by a combination of woven roving (WR) and chopped strand mat (CSM) glass fibers with an unsaturated polyester matrix. The composite specimens were produced using a press mold method for controlling the thickness of specimens. Composites were tested with a burning test apparatus, flexural bending machine and Izod impact tester. Composites were also analyzed by SEM, TGA, DSC, FT-IR spectroscopy and macro photographs. The addition of nAFPP and reducing the amount of ATH increased ignition time significantly and decreased the burning rate of specimens. The higher content of nAFPP significantly increased the flexural and impact strength. TGA analysis shows that higher ATH content had a good contribution to reducing specimen weight loss. It is also strengthened by the lower exothermic of the specimen with higher ATH content. The use of SS and BA inhibited combustion by forming charcoal or protective film; however, excessive use of them produced porosity and lowered mechanical properties.