Cleaning & Maintenance: Focus on carpet fiber - April 2014

By Darius Helm

The cleanliness of carpet is a partnership between the cleanability of the product and the quality of the maintenance program. It has been noted extensively over the years that, when using identical cleaning and maintenance protocols, outcomes vary depending on the type of carpet being cleaned. And these days, there is more variety in carpet than ever before, from designs to constructions to fiber types, in both the residential and commercial markets.

Several factors determine the cleanability of carpet, including constructions, weights, filament size, twist, dyeing technique, soil and stain treatments, fiber cross-sections, and fiber types. They can all impact cleaning time, how much cleaning chemistry is needed, and how the carpet will wear over time. 

Cleaning professionals who know details about the product are in a better position to both offer good service and utilize their resources efficiently. For instance, contract dealers that both install and maintain commercial carpet or, on the residential side, retailers with cleaning programs have a big advantage over typical janitorial services or independent residential cleaning operations because of their knowledge of the installed products.

CLEANABILITY FACTORS
Regardless of the cleaning system being used, the composition and construction of the carpet impacts the efficacy of the cleaning. Pile heights and density are the first barriers. Professional Testing Laboratory of Dalton, Georgia (see box on page 50) tested a variety of carpets, both residential and commercial, with weights ranging from 18 ounces to 100 ounces, and found that soil removal using the exact same vacuum cleaner with four passes over the carpets captured over 80% of the material from the lowest pile heights and only 15% from the highest piles.

The laboratory also compared loop and cut pile, and determined that for daily maintenance protocols loop pile performed better, because dirt was slower to penetrate deep into the carpet, but once the dirt became embedded, removal rates were somewhat higher with cut pile. 

As a general rule, the greater the surface area, the more dirt can be trapped. That’s why, for instance, feather dusters are so effective at trapping dust. Feathers are made of barbed filaments with tremendous surface area. The recent wave of ultra-soft fibers in the residential market feature is based on synthetic filaments (of nylon, PET and triexta) thinner than any previously used in carpet. And thinner filaments means more surface area per square foot for dirt to attach itself to. 

To some extent, the profile of the filaments themselves impact surface area. Most synthetic carpet fibers have a cross-section of some sort of trilobal shape, from softened triangles to thinner Y shapes to triangles with bulbous lobes. It’s a design that both hides soil and adds sparkle to the fiber. 

It’s worth noting that the most unique synthetic carpet fiber cross-section is found in Invista’s Antron hollow filament nylon 6,6 commercial fiber, a softened square shape with four holes running down its length. It offers a smaller surface area than trilobal constructions, and the holes down the middle are designed to act as prisms and also enhance the product’s performance.

Stain resistance is a big issue in carpet cleaning. Fundamentally, there are two ways in which dye is conveyed onto fiber. One is solution dyeing, which essentially embeds pigment molecules into the structure of the polymer during the extrusion process. The other is acid dyeing, which takes several forms, all of which function to attach acid dyes to dye sites on the polymer. Solution dyeing leaves all of the dye sites open, while acid dyeing only leaves a portion of them open. And since dye sites are also stain sites, fiber colored either way is susceptible to staining.

Mills deal with this issue in several ways, depending somewhat on the fiber type, but the general rule is stain resist treatments that lock onto the open dye sites, which prevents them from taking up wayward stains.

Then there’s the issue of soiling. Some synthetic fibers attract oil, like polypropylene and polyester, while the nylons attract water. Those that attract oil soil more easily and generally need some sort of soil protection, but nylons also often feature soil resist finishes.

When it comes to soil and stain treatments, it’s worth noting that they hold up well against cleaners, as long as those cleaners conform to CRI’s recommendations and don’t go over a pH of 10. However, they don’t hold up well against abrasion from dry soil, which will scrape off the finish and leave the carpet fibers vulnerable. That’s why the warranties of five years or so that come with these treatments don’t apply to product installed on stairs, where the abrasion rate is much higher.

INHERENT FIBER QUALITIES
Then there are the fiber types. While the different mills and fiber producers all have their own proprietary chemistries and technologies to protect their carpets, enhance durability and resist stains and soiling, each and every one contends with the same scientific conditions when it comes to the polymers they use, and each of those polymer fibers have distinct characteristics that relate to cleanability. The quality of the different carpets from the various mills hinges on how the strengths of the different fibers are leveraged and how their weaknesses are neutralized. And the success of the technologies and chemistries is heavily dependent on performing the specific maintenance recommendations. 

So just because, for instance, polyester is oleophilic (attracted to oil) doesn’t mean that all polyester carpets are equally oleophilic and hence more prone to soiling. And it doesn’t mean that there aren’t specific polyester carpets that outperform certain carpets made of fibers that don’t naturally attract oil, like nylon.

Also, there are advantages and disadvantages to every fiber type. For instance, the most oleophilic fiber out there is polypropylene, which is mostly used in machine-made area rugs, and to a far lesser extent in mainstreet carpet and lower end residential carpet. And it also happens to have phenomenal stain resistance because it has no dye sites, which is why polypropylene fiber is solution-dyed.

Polypropylene, which is chemically inert, can be cleaned with just about anything, including low and high pH chemistries. Even bleach won’t hurt it. But it soils easily and holds onto oil, and it lacks the resilience of the other fibers, so it will crush easily. It also has a much lower melting point than the other fibers, and friction will melt it. So when cleaning polypropylene, it can take harsh chemicals but not harsh treatment.
A much more significant fiber is polyester, which has been taking share in the residential and multi-family markets. It’s also stain resistant, though not as stain resistant as polypropylene. And it’s oleophilic, also less so than polypropylene. And it’s more resilient than polypropylene but less resilient than nylon. Quality solution-dyed polypropylene and polyester are scoured to remove finishing oils, but it’s not uncommon to find carpet out there with lubricant still clinging to it, a condition that will only deteriorate without a deep cleaning.

Because polyester is not as resilient as nylon, the fiber is given a higher twist level, and over time in high traffic areas the fibers break down somewhat—which is one of the reasons why polyester isn’t specified in the commercial market. Because the greying effect is in high traffic areas, a cleaning professional may mistakenly think it needs more aggressive cleaning, which would waste resources and only make matters worse.

A lot of low-end polyester goes into the multi-family market, and it’s often not scoured. And regular cleaning regimens are generally in short supply in rental properties, so the soiling problem gets exacerbated and the carpet quickly degrades. Even if the polyester carpet has a soil treatment, without a regular cleaning regimen dirt will abrade the fiber, removing the treatment, and the carpet will soil.

Nylon 6 and nylon 6,6 are not inherently stain resistant, but they’re hydrophilic (attracted to water), so they have better resistance to soiling. Over the last decade, nylon 6 has taken a lot of marketshare from nylon 6,6 with the vertical integration of the big mills. Nylon 6,6 is produced by independent fiber manufacturers like Invista, Ascend and Universal.

In some ways nylon 6 and 6,6 are very similar. Both are high performance fibers with good resilience, and durability sufficient for all commercial segments. In some ways, nylon 6,6 has natural advantages. Both fibers can stain, but in general nylon 6 takes acid dye somewhat more readily than nylon 6,6, which means that it also stains more easily. However, stain resist technologies, properly maintained with cleaners up to a pH of 10 to avoid stripping away the acid dye blocks, reduce the significance of those differences. So while the two fiber types may perform equally well when new, it’s a different story if maintenance is inadequate in preventing the treatments from being scraped off.

Another difference between the fibers is that nylon 6,6 absorbs more water than nylon 6, so low moisture encapsulation systems can be more efficient than, for instance, hot water extraction systems.

Steve Spencer, a facility specialist at State Farm, encountered a unique situation at a 350,000 square foot facility he was working with in Phoenix ten or so years ago. He had specified a multicolored heather pile broadloom in the building from Antron, which was part of DuPont back then. A few years later he was informed that all the carpet wasn’t holding up well. The carpet had been installed in two spaces separated by a wall, and each space received equal traffic and the same maintenance regimen. However, the carpet on the left was not faring as well as the carpet on the right, and Spencer found out that it was identical in every way (same weight, same backing, both solution dyed) to the Antron nylon 6,6 product on the right, but in the specification process the carpet on the left ended up being made of nylon 6. A close examination of samples revealed that the fibers were brittle and discolored with all of the multicolor fading except for blue.

It’s worth noting that this was at least a decade ago, before the mills vertically integrated and started pouring R&D dollars into ensuring that their nylon 6 could perform. But the lesson from the anecdote is that all carpets are not equal and they don’t clean equally well. And the best way to get the performance required is to know the product’s characteristics and maintain it accordingly.

LESSONS FROM THE FIELD
When Spencer first started managing facilities 20 years ago, the carpet was switched out every six years. But since then he has developed a suite of strategies that has allowed him to consistently keep carpet down in good condition for up to 15 years. First and foremost is his strategy for keeping out soil, because he credits abrasion from dry dirt as having the biggest impact on carpet deterioration. So he traps dirt in walk-off mats and has the main and central aisles vacuumed every day. Though he’ll use a range of cleaning technologies, including hot water extraction, low moisture encapsulation and dry systems like Capture and Host, he’ll do an annual flushing once a year until the water runs clear.

Spencer doesn’t specify carpet with soil or stain treatments because, in his experience, the treatments generally don’t last. Instead, he relies on solution-dyed nylon.

Related Topics:Mohawk Industries, Carpet and Rug Institute