Short answer……yes.
Now before you sit back and exclaim “no they are not” hear me out for a second.
I’m not talking the plastic knives you get in picnic sets, or the cheap ones from the local corner takeaway food shop.
I am talking the clinically manufactured Polypropylene and Zytel daggers and darts on the market today.
Now without getting to deep into the scientific and molecular structure of the daggers and darts, for arguments sake lets just say plastic, because as a base thats what they are. All be it a very strong and deadly plastic.
Cold steel have a range of products made out of this material. Virtually indestructible, and when a Arnis Stick or baseball bat made of it is wielded in anger, you can see the result on many youtube videos.
Below is one of the daggers I have. Made entirely of the deadly plastic it is capable of piercing a watermelon up to the bolster/heel/finger guard and moving on to the next. No upkeep required other than a cleaning, never rusts, undetectable by metal detectors (for obvious reasons) and most importantly well and truly looks the part if the time ever comes to draw it.
Cold Steel also have darts constructed of “Zytel”..A glass filled nylon which is stated to be a “abrasion and impact resistant thermoplastic”.
Now being a dedicated fan of cold hard steel, I still cannot help but wonder if the future of edged weapons will be products like these. They are lightweight, strong and comparatively priced, and have an ever expanding range of options. Daggers, Darts, bats, sticks..the list is growing. Has self defence and survival taken up the green earth challenge of recycling?!
I grew up with steel. To me there is nothing that compares. Its not just about the look or feel when you use it, its about the time you take to maintain it, and the respect that you give it.
But I have to say, I can see my collection expanding to include some of these new environmentally friendly options….Afterall they are still a very cool and functional weapon 
I would love to have a few daggers like these, but I do not think steel will ever be replaced for swords as far as durability goes. Speaking of Cold Steel, I would also love to get the Indian War Club or the Gun Stock War Club. Yes, these plastic blades are deadly, as anything can be. Even plastic butter knives can kill, especially if you break it off into a shiv.
Please forgive me for the only partially coherent comment. I am very tired for whatever reason.