日前，ACC美國(guó)化學(xué)理事會(huì) (American Chemistry Council) 和美國(guó)密歇根州立大學(xué) (MSU) 的研究人員展示了一種新型“可逆性”多材料連接粘合劑。這種粘合劑的特別之處可以讓修復(fù)/重連之后的粘接更為牢固，而這種特性將極大地便利一些大量采用碳纖維增強(qiáng)材料 (CFRP) 車型的維修保養(yǎng)和報(bào)廢回收。
在美國(guó)密歇根州特拉弗斯市舉辦的管理研討會(huì) (MBS) 期間，美國(guó)索爾維特種聚合物 (Solvay Specialty Polymers) 公司汽車業(yè)務(wù)發(fā)展經(jīng)理、美國(guó)化學(xué)理事會(huì)汽車工作組現(xiàn)任輪值主席 Sandra McClelland表示，“今年，研究人員發(fā)現(xiàn)，我們可以使用這種粘合劑進(jìn)行部件粘合，而后將粘合的部件分離，最后再次進(jìn)行二次粘合，而‘愈合’后的新連接甚至比第一次粘合更加牢固。這意味著，經(jīng)過這種膠水的修復(fù)，一個(gè)在車禍中受到損壞的碳纖維車架可能比碰撞之前更加結(jié)實(shí)，而里程已經(jīng) 50,000 英里的車輛進(jìn)行修復(fù)，車輛的碳纖維車架甚至比出廠時(shí)更加結(jié)實(shí)。”
McClelland 介紹了索爾維公司與密歇根州立大學(xué)復(fù)合汽車研究中心 (Composite Vehicle Research Center) 及 Mahmoodul Haq 博士在可逆性多材料粘接合作研究項(xiàng)目中的最新發(fā)現(xiàn)。這種新型粘接劑的研發(fā)，主要是為了滿足汽車行業(yè)對(duì)連接技術(shù)的多項(xiàng)要求，包括：不同材料（塑料、鋼、鋁和復(fù)合材料）的連接、車輛減重、連接牢固性（ASTM 美國(guó)材料與試驗(yàn)協(xié)會(huì)的結(jié)構(gòu)效率測(cè)試）、45 秒內(nèi)完成粘接工序，以及連接過程可逆等。也就是說，粘接后的部件可以在當(dāng)?shù)剀噺S的維修保養(yǎng)環(huán)節(jié)中分離，并“重新進(jìn)行連接”，使車輛報(bào)廢后的復(fù)合材料回收也將更加便捷快速。
在管理研討會(huì)上，McClelland 表示，這種“神奇的膠水”是美國(guó)化學(xué)理事會(huì)和密歇根州立大學(xué)的聯(lián)合研究成果，目前看來可以滿足汽車行業(yè)的上述各種要求。這種熱塑性粘合劑的另一個(gè)特殊之處在于，可以將需要連接的組件接縫完全連接在一起，而非僅連接部分粘接點(diǎn)。此外，由于連接處的擴(kuò)展應(yīng)力“相當(dāng)強(qiáng)”，廠商還可以顯著減少這種粘合劑的用量，從而實(shí)現(xiàn)額外的車輛減重效果。
可逆性過程
McClelland 表示，這種熱塑性粘接劑可以在不到 1 分鐘內(nèi)完成融化、分離、重連的完整過程，完全符合車輛裝配廠對(duì)粘接工藝的速度要求。具體來說，這種可逆性粘接劑內(nèi)含大量磁性納米鐵微球，而這些金屬納米顆粒將在電流通過時(shí)產(chǎn)生振動(dòng)，并在幾秒內(nèi)快速升溫至很高的溫度（300 到 800°F 之間），從而在周圍材料開始變熱之前完成融化分離過程。此后，這種粘合劑還可以在幾秒鐘內(nèi)硬化，也就是從本質(zhì)上成為了一種可是隨時(shí)滿足融化分離和重新粘接需求的“快干膠水”。
密歇根州立大學(xué)的研究人員首先使用加熱的粘接劑連接多種不同材料，而后對(duì)這些連接處進(jìn)行了失效測(cè)試，并按照 ASTM 協(xié)會(huì)對(duì)抗疲勞強(qiáng)度、剪切應(yīng)力、沖擊應(yīng)力、彎曲蠕變模量等參數(shù)的標(biāo)準(zhǔn)，評(píng)估這些連接處的結(jié)構(gòu)效率。此后，研究人員利用電磁線圈在 30 秒內(nèi)重新融化粘合劑，并對(duì)“愈合”后的新連接進(jìn)行平行重復(fù)試驗(yàn)。數(shù)據(jù)表明，新形成的連接更牢固。
McClelland 表示，“通過融化粘合劑并重新賦予它所需的能量，新連接的結(jié)晶程度比之前更高，而聚合物的結(jié)晶程度可以在一定程度上決定該聚合物的強(qiáng)度。”
McClelland補(bǔ)充說，研發(fā)人員將首先嘗試降低這種粘接劑的成本，然后逐步進(jìn)行商業(yè)化推廣，但目前尚未制定具體的時(shí)間計(jì)劃。
據(jù) McClelland介紹，“這種粘接劑具備在修復(fù)后更加牢固的特點(diǎn)，可以在一定程度上解決汽車行業(yè)所面對(duì)的‘連接點(diǎn)’疲勞問題。”
The American Chemistry Council (ACC) and researchers at Michigan State University (MSU) have demonstrated a new “reversible” adhesive for multi-material joining that becomes stronger after use and repair/rebonding—a significant development for the repairability and end-of-life recyclability of CFRP-intensive (carbon-fiber-reinforced polymer) vehicles, for example.
“What the researchers found this year is when you bond it, unbond it, and then rebond, the ‘healed’ new bond actually becomes stronger than the original bonds. That means that a repaired carbon-fiber frame could be stronger in a crash after the repair. This also means getting an auto frame repaired at 50,000 miles can literally mean the car is better than new,” Sandra McClelland, automotive business development manager, Solvay Specialty Polymers USA and presenting chair, ACC Auto Team, said at the Management Briefing Seminars (MBS) in Traverse City, MI.
McClelland described the latest discoveries in multi-material reversible bonding, in collaboration with MSU’s Composite Vehicle Research Center and Dr. Mahmoodul Haq. The alternative adhesive connector attempts to satisfy several auto-industry goals for a joining technology, apart from working in multi-material applications (plastics, steel, aluminum, and polymer composites): reduced weight, binds as robustly as other connectors (ASTM testing for structural efficiency), applies and adheres in 45 seconds and is reversible—meaning the bond can come apart and be “re-joinable” in a local repair shop or at end-of-life for faster and easier recycling of composites.
This “magic glue,” as McClelland referred to it at MBS, was developed through collaboration between ACC and MSU and appears to satisfy these criteria, she said. The thermoplastic adhesive material grips the entire seam of a joint, not just one spot as with some other types of connectors. Spreading stress results in “considerably stronger” joins, which can enable additional weight savings because parts joined can be subsequently thinner and lighter.
Process for ‘reversibility’
The thermoplastic adhesive can melt apart and rebond in less than a minute, the amount of time required in an assembly plant, McClelland noted. The material contains magnetic nanoparticles—iron microspheres that vibrate with electric current and become very hot, 320 to 800°F within seconds, melting the thermoplastic adhesive before the surrounding material heats up. It then can harden in seconds—essentially becoming fast-acting glue that bonds and rebonds on demand.
After MSU researchers apply warm glue to bond the multi-materials, they test the joints to failure and record structural efficiencies by ASTM standards for joint fatigue, strength, shear, impact, flex, creep and modulus. The researchers then use electromagnetic coils to re-melt the adhesive in 30 seconds and establish a new “healed” bond to conduct parallel duplicate tests. The data shows this new re-bond is stronger.
“By melting the adhesive and giving it all that energy, that material becomes more crystalline than it was initially. A more crystalline polymer has better strength,” McClelland said.
The adhesive will be economically feasible and eventually commercially available, she added, but did not state a specific timeframe.
“Strengthening after repair could stand the automotive notion of joint fatigue on its head,” she said.
Author: Ryan Gehm
Source: SAE Automotive Engineering Magazine
研究表明，一種新型“可逆性”膠水可讓修復(fù)/重連后的粘接更加牢固。（圖片來源：美國(guó)化學(xué)理事會(huì)）
這種可逆性粘合劑可以在車輛的維修保養(yǎng)和報(bào)廢回收過程中發(fā)揮巨大作用，特別是對(duì)BMW i8 等大量采用碳纖維增強(qiáng)材料的車型來說，尤其如此。（圖片來源：BMW） 