Salvaging PCB waste: Fibreglass resin from discarded circuit boards is safe to reuse in composite products

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  • Published: Feb 6, 2012
  • Author: Steve Down
  • Channels: Gas Chromatography
thumbnail image: Salvaging PCB waste: Fibreglass resin from discarded circuit boards is safe to reuse in composite products


Recycling PCBs

The sheer amount of electronic waste discarded throughout Europe led directly to the Waste Electrical and Electronic Equipment Directive (WEEE) which aims to encourage its reuse, recycling and recovery. Regrettably, regulations are not in force around the world and some countries have massive dumps of electronic goods like mobile phones, computers and white goods.

One problem country has been China where large illegal dumps have been steadily growing and where backyard recycling is the norm. Here, e-waste is incinerated to recover the heavy metals, releasing plumes of toxic vapours into the environment. However, if waste like printed circuit boards (PCBs) is recycled at industrial plants, the recoveries of metals such as copper, aluminium and tin and precious metals like gold, silver and platinum can be high, since they constitute up to 28% of the PCBs.

Once the metals are removed, much of the residual waste consists of fibreglass resin and this is normally discarded into landfills. However, some scientists have recognised the potential of this waste material, deploying the fibreglass resin portion (FRP) as a filler for other types of products like bricks and modified polymers.

One group of Chinese scientists has made three kinds of product in which the FRP constituted up to 40% of the content, acting as reinforcement. It was used directly without modification to produce a phenolic moulding compound (PMC), a wood plastic composite (WPC) and a non-metallic dough which could be moulded into disks.

Although these products will have many applications, their safety must be assured first, bearing in mind that the FRP originates from PCBs and could be contaminated with metals and organic additives. So, the same Chinese team, Zhenming Xu, Jie Guo, Ying Jiang and Xiaofang Hu from Shanghai Jiao Tong University, have undertaken a two-part study to check the volatile compounds and metals present in the new composites.


Volatiles from composite products

Composite granules were prepared from high-density polyethylene (HDPE), wood flour and other additives along with 15% FRP before extrusion into a WPC product. The NMP product containing 20% FRP was prepared by hot pressing a mixture that contained a polymeric resin paste and the PMC product was made from a moulding powder that also contained 20% FRP.

The volatiles emitted from the FRP and all three products were assessed by GC/MS linked with headspace sampling on an activated carbon fibre or thermal desorption into Tenax TA tubes. They were resolved on a low-polarity, bonded and crosslinked column designed for the optimum resolution of volatiles and analysed by electron ionisation. The individual compounds were then identified by searching a commercial mass spectral database and measured using calibration curves derived from authentic standards.

The metals present in the samples were analysed by inductively coupled plasma atomic emission spectrometry after leaching into glacial acetic acid in experiments designed to simulate landfill leaching under a worst case scenario.


Fibreglass resin recycled safely

The dominant volatile in the moulding powder and the subsequent PMC product was phenol, estimated at 60 and 962 µg/m3, respectively. So, final processing to make the product reduces the phenol level by nearly 94% to a value which is less than its odour threshold. More importantly, it is also well below the "lowest observed adverse effect level" for respiratory irritation in humans which stands at 4420 µg/m3. The phenol originated from phenolic resin that is added to the moulding powder.

A broader spectrum of volatiles was detected in the WPC product but they were all at relatively low concentrations. Phenols, aldehydes and alkanes were found and, once again, they did not originate from the FRP filler. Most of them were in the wood flour, including benzaldehyde and the C8-C10 aldehydes. The levels of the hazardous compounds phenol and styrene were "not major concerns in risk-based assessment."

The third product was NMP and it emitted fewer detectable volatiles than WPC, the major one being styrene at 633 µg/m3, which is above the odour threshold but below the reference level set by the US EPA for exposure by inhalation. Styrene is added as a crosslinking agent for the polymeric resin and the other volatiles included ethylbenzene, o-xylene, benzaldehyde and phenol which were also released primarily from the resin.

So, in all cases, the volatiles detected in the composite products did not originate from the recycled FRP filler but from other added components, indicating that the filler is safe in this respect.

The metal leaching experiments showed that the FRP was hazardous due to the amount of residual copper in the leachate, which was 8 times greater than the identification standard. Microscopy images revealed that the metal was present as fine particles. However, once the composites were prepared, the copper particles were effectively bound within the resin matrix, preventing them from leaching out.

These tests imply that the FRP is safe to use from both environmental and health points of view and can be recycled in various forms to help manufacture products like manhole covers and park benches. It will require more intervention from commercial and government sources to bring this to fruition and prevent the widespread dumping of fibreglass resin recovered from printed circuit boards.

 


 


This article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

  
The fibreglass resin sections that are recovered from printed circuit boards and recycled into new composite products are not contaminated with hazardous volatile organic compounds, says a team of Chinese scientists. All volatiles detected originate from the other added components

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